The increase in antimicrobial resistance (AMR) poses a massive threat to world health, necessitating the urgent development of alternative antimicrobial growth control techniques. Due to their specific physical and chemical properties, nanomaterials, particularly carbon-based nanomaterials, have emerged as attractive candidates for antimicrobial applications, however, reviews are lacking. This comprehensive review aims to bridge the existing knowledge gaps surrounding the mechanism and significance of nanobiochar (NBC) and carbon nanostructures in the field of antimicrobial applications. Notably, NBC, which is derived from biochar, exhibits promising potential as an environmentally-friendly substance with antimicrobial properties. Its strong adsorption capabilities enable the removal and immobilization of pathogens and pollutants from soil and water and also exhibit antimicrobial properties to combat harmful pathogens. In addition to NBC, carbon dots (CDs) and graphene oxide (GO) have also shown excellent antimicrobial properties. These carbon-based nanomaterials find applications in agriculture for phytopathogen control and post-harvest disease management, as well as in medicine for nanotheranostics and in the food industry for extending shelf life as an eco-friendly alternative to chemicals and antibiotics. However, the long-term toxicity of these nanoparticles to humans and the environment needs further investigation, considering the influence of different physiochemical characteristics on antimicrobial properties and nanotoxicity. Therefore, continued exploration in this area will pave the way for future research and safe deployment strategies of carbon-based nanomaterials in combating microbial threats.
| • | Nanobiochar and carbon dots are promising alternatives to traditional antimicrobial methods. |
| • | Nanobiochar demonstrates strong adsorption and pathogen immobilization properties. |
| • | Carbon dots and graphene oxide show excellent antimicrobial properties. |
Biochar has been widely recognized for its potential to increase carbon (C) sequestration and mitigate climate change. This potential is affected by how biochar interacts with native soil organic carbon (SOC) and fresh organic substrates added to soil. However, only a few studies have been conducted to understand this interaction. To fill this knowledge gap, we conducted a 13C-glucose labelling soil incubation for 6 months using fine-textured agricultural soil (Stagnosol) with two different biochar amounts. Biochar addition reduced the mineralization of SOC and 13C-glucose and increased soil microbial biomass carbon (MBC) and microbial carbon use efficiency (CUE). The effects were found to be additive i.e., higher biochar application rate resulted in lower mineralization of SOC and 13C-glucose. Additionally, soil density fractionation after 6 months revealed that most of the added biochar particles were recovered in free particulate organic matter (POM) fraction. Biochar also increased the retention of 13C in free POM fraction, indicating that added 13C-glucose was preserved within the biochar particles. The measurement of 13C from the total amino sugar fraction extracted from the biochar particles suggested that biochar increased the microbial uptake of added 13C-glucose and after they died, the dead microbial residues (necromass) accumulated inside biochar pores. Biochar also increased the proportion of occluded POM, demonstrating that increased soil occlusion following biochar addition reduced SOC mineralization. Overall, the study demonstrates the additional C sequestering potential of biochar by inducing negative priming of native SOC as well as increasing CUE, resulting in the formation and stabilization of microbial necromass.
| • | Biochar showed additional C storage ability by preserving SOC from mineralization (negative priming) and stabilizing added labile organic substrate |
| • | Biochar (30 Mg ha−1) significantly increased microbial carbon use efficiency |
| • | Biochar increased the formation of stable microbial residues (necromass) from a labile substrate (glucose) added to soil, as indicated by 13C recovery in amino sugars |
The significant volatilization of NH3 during aerobic composting causes nitrogen (N) losses and environmental risks. Both iron (Fe) and biochar (BC) can influence the N conversion process in composting. Fe application can delay the maturation of materials, while biochar can enhance the quality of organic fertilizer. The combination of these two conditioners may help decrease NH3 emissions and improve organic fertilizer quality. Therefore, this study investigates the effects of different doses of FeCl3 and BC on NH3 emissions and organic fertilizer quality during composting. The results demonstrated that Fe/BC co-conditioners reduced the accumulation of NH3 emissions during composting by 11.1–48.2%, increased the total nutrient content by 0.6–15.3%, and enhanced economic and environmental benefits by 0.1–23.6 $ t−1. At the high-temperature stage of composting, Fe/BC co-conditioners decreased the pH by 0.3–1.2, but there was no significant difference compared to the control at the end of composting, and they did not affect compost maturation. The structural equation model analysis suggested that the reduction in NH3 emissions was related to ammonia-oxidizing bacteria (AOB), NH4 +–N, and total nitrogen (TN). As a result, the Fe/BC co-conditioners reduced NH3 emissions by lowering the pH at the beginning of composting and increasing the content of NH4 +–N. This study concludes that Fe/BC co-conditioners could complement each other to significantly reduce NH3 emissions and improve the quality of organic fertilizers.
| • | Different doses of ferric chloride and biochar (Fe/BC) were used for aerobic composting. |
| • | Fe/BC co-conditioning composting significantly reduced NH3 volatilization. |
| • | Fe/BC co-conditioning composting enhanced N retention and total nutrients. |
| • | NH3 emission reduction was mainly related to AOB, NH4 +–N and TN during composting. |
| • | Fe/BC co-conditioning composting could enhance economic and environmental benefits. |
Biochar and organic fertilizer are widely supported to maintain crop production and sustainable development of agroecosystems. However, it is unclear how biochar and organic fertilizer alone or in combination regulate soil functional microbiomes and their relationships to ecosystem multifunctionality (EMF). Herein, a long-term (started in 2013) field experiment, containing five fertilization treatments, was employed to explore the effects of biochar and organic fertilizer applications on the EMF (based on 18 functional indicators of crop productivity, soil nutrient supply, element cycling, and microbial biomass) and the functional microbiomes of bulk soil and rhizosphere soil [normalizing the abundances of 64 genes related to carbon (C), nitrogen (N), phosphorus (P), and sulphur (S) cycles]. Compared with single-chemical fertilization, biochar and organic fertilizer inputs significantly enhanced most ecosystem-single functions and, in particular, the EMF significantly increased by 18.7–30.1%; biochar and organic fertilizer applications significantly increased the abundances of soil microbial functional taxa related to C-N-P-S cycles to varying degree. The combined application of biochar and organic fertilizer showed a better improvement in these indicators compared to using them individually. Most functional microbial populations in the soil, especially the taxa involved in C degradation, nitrification, nitrate-reduction, organic P mineralization, and S cycling showed significantly positive associations with the EMF at different threshold levels, which ultimately was regulated by soil pH and nutrient availability. These results highlight the strong links between soil microbiomes and agroecosystem functions, as well as providing scientific support for inclusion of biochar in agricultural production and services with organic amendments.
| 1. | 8-year field evidence revealed impacts of biochar and pig manure on soil functional microbiome and ecosystem functions. |
| 2. | Biochar and pig manure inputs notably enhanced most ecosystem-single functions and the EMF increased by 18.7–30.1%. |
| 3. | Biochar and pig manure inputs notably enriched soil functional microbes related to C-N-P-S cycles to varying degree. |
| 4. | Increase in EMF was related to microbe-driven soil processes such as C degradation, nitrification, and Po mineralization. |
| 5. | Inclusion of biochar in crop production with organic amendments could enhance agro-ecosystem functions and services. |
Biochar production from woody biomass generated during forest management (slash) offers significant benefits for soil health and carbon emissions, yet its adoption remains limited in the western United States (U.S.). To address this challenge, the U.S. Department of Agriculture (U.S.D.A.) Forest Service Rocky Mountain Research Station organized two workshops focused on forest management-centric biochar production. These workshops convened a diverse group of stakeholders, including investors, land management practitioners, industry professionals, and research scientists, each with unique roles in slash-based biochar production. This article presents a synthesis of the insights and perspectives gathered from these workshops, aiming to identify barriers and propose viable pathways for overcoming them. The barriers encompass governance issues such as policy and permitting, economic challenges related to costs, funding, and market stability, technological hurdles concerning methods and equipment, and a need for further research and improved science dissemination. In response to these challenges, workshop attendees collaboratively outlined specific strategies to reduce these barriers. These strategies emphasize the expansion of operational initiatives, the development of proactive policies, the stabilization of biochar markets, and the generation of additional case studies showcasing the effects of biochar amendments across various soils and environments. Collectively, the insights gleaned from this workshop series provide a comprehensive roadmap outlining both the struggles and the necessary actions and investments required to enhance the scale of slash-based biochar production and application in the western U.S.
| • | Intertwined policy, economic, technology, and knowledge barriers underpin pervasive biochar adoption issues. |
| • | Managers face pervasive challenges with permitting, slash handling costs and uncertain biochar application benefits. |
| • | Pathways forward involve setting goals, streamlining permits, enhancing science communication, and further case studies. |
Iron-carbon micro-electrolysis system is a promising method for promoting electron transfer in nitrate removal. However, many traditional approaches involving simple physical mixing inevitably suffered from the confined iron-carbon contact area and short validity period, leading to the overuse of iron. Here, a ceramsite-loaded microscale zero-valent iron (mZVI) and acidified carbon (AC) coupled-galvanic cell (CMC) was designed to support chemical, autotrophic and heterotrophic denitrification. Long-term experiments were conducted to monitor the nitrogen removal performance of denitrification reactors filled with CMC and thus optimized the denitrification performance by improving fabrication parameters and various operating conditions. The denitrification contributions test showed that the chemical denitrification pathway contributed most to nitrate removal (57.3%), followed by autotrophic (24.6%) and heterotrophic denitrification pathways (18.1%). The microbial analysis confirmed the significant aggregation of related denitrifying bacteria in the reactors, while AC promoted the expression of relevant nitrogen metabolism genes because of accelerated uptake and utilization of iron complexes. Meanwhile, the electrochemical analysis revealed a significantly improved electron transfer capacity of AC compared to pristine carbon. Overall, our study demonstrated the application of a novel mZVI-AC coupled material for effective nitrate removal and revealed the potential impact of CMC in the multipathway denitrification process.
| • | Novel mZVI-AC coupled micro-electrolysis systems were established for denitrification |
| • | Chemical, autotrophic and heterotrophic denitrification pathways were observed in reactors |
| • | AC increased the activity of enzymes encoding denitrification and respiratory chains |
| • | The acidification brought greater capacitance and lower impedance to carbon to facilitate iron oxidation |
The use of machine learning (ML) in the field of predicting heavy metals interaction with biochar is a promising field of research, mainly because of the growing understanding of how removal efficiency is affected by characteristic variables, reaction conditions and biochar properties. The practical application in biochar still faces large challenges, such as difficulties in data collection, inadequate algorithm development, and insufficient information. However, the quantity, quality, and representation of data have a large impact on the accuracy, efficiency, and generalizability of machine learning tasks. From this perspective, the present data descriptors, the efficiency of machine learning-aided property and performance prediction, the interpretation of underlying mechanisms and complicated relationships, and some potential ways to augment the data are discussed regarding the interactions of heavy metals with biochar. Finally, future perspectives and challenges are discussed, and an enhanced model performance is proposed to reinforce the feasibility of a particular perspective.
| • | A high growth rate of studies on the application of machine learning (ML) in biochar in recent years. |
| • | ML interpretability of heavy metals (HMs) interaction mechanisms with biochar is explicated emphatically. |
| • | Challenges and perspectives of ML application in the removal of HMs by biochar. |
| • | Combining an advanced machine learning technique to achieve better predicted performance. |
In order to treat dyes in the wastewater of the printing industry and to reutilize walnut shell (WS) waste generate economic benefits, supercritical carbon dioxide (SC-CO2) pretreatment technology was developed to prepare porous biochar as a precursor for adsorption material. Orthogonal experiments were conducted at the temperatures of 200, 300, and 400 ℃ with durations of 20, 40, and 60 min, and a control group was set up using N2 pretreatment. Then, KOH activation was employed to prepare biochar adsorption material. The biochars were analyzed and characterized using TGA, BET, SEM, FT-IR, and XRD, and the liquid and gas phase products of the pretreatment process were analyzed semi-quantitatively and quantitatively using GC–MS and gas chromatography. Methylene blue (MB) dye was selected as an indicator to measure the adsorption capacity of biochar, and adsorption kinetics were analyzed based on the data. The results indicate that pretreatment with SC-CO2 effectively enhanced the performance and yield of the activated carbon. The highest specific surface area increased by 18%, and the maximum adsorption of MB increased by 23% compared to the N2 control group. The yield increased by 8–262% and the specific surface area increased by 50–192% compared to the direct activation of walnut shell (WS). During the pretreatment processes for the preparation of biochar adsorption material with the best specific surface area, phenol-enriched bio-oil was produced as a by-product which has economic value.
| 1. | The poly-generation of biochar precursor and bio-oil could be realized by supercritical CO2. |
| 2. | Prepared activated carbon had great physical performance and excellent dye adsorption capacity. |
| 3. | The pretreatment process produced high-value organic liquid by-products. |
| 4. | Mild pretreatment conditions were more advantageous. |
Modification serves as an excellent approach to enhancing the adsorption performance of biochar for tetracycline. Selective modification further allows the attainment of biochar materials that are not only more efficient but also cost-effective. However, the key structural factors influencing the adsorption of tetracycline by biochar remain unclear at present, hindering the effective guidance for modification strategies. This study established the relationship between carbonization degree and adsorption capacity, constructed a standardized microscopic model for biochar adsorption of tetracycline, and explored potential reaction mechanisms. The results indicated that with increases in the degree of carbonization, the tetracycline adsorption capacity of biochar increased from 16.08 mg L−1 to 98.35 mg L−1. The adsorption energy exhibited a strong correlation with the aromatic condensation of biochar at p ≤ 0.01, with a linear relationship (r2 ≥ 0.94). For low carbonization degrees, the adsorption of tetracycline by biochar was primarily driven by chemical bonds (69.21%) and complemented with electrostatic interactions, weak van der Waals forces or π-π interactions. For high carbonization degrees, the synergistic effects of hydrogen bonding, van der Waals forces, and π-π interactions determined the adsorption of tetracycline on biochar (91.1%). Additionally, larger carbon clusters resulted in stronger and more stable adsorption interactions. Furthermore, carboxyl-functionalized highly carbonized biochar displayed the highest reaction energy of − 1.8370 eV for adsorption of tetracycline through electrostatic interactions. This study suggests that a high degree of aromatic condensation in the carbon structure of biochar is crucial for the efficient adsorption of tetracycline.
| • | Low-carbonized biochar primarily adsorbs tetracycline through chemical bonds. |
| • | High degree of aromatic condensation facilitates biochar adsorption of tetracycline. |
| • | -COOH provides the highest binding affinity for tetracycline adsorption by high-carbonized biochar. |
In addition to the adsorption and immobilization capacities of iron-modified biochars, these materials produce persistent free radicals (PFRs) that can carry out metal [i.e., Cr(VI)] redox transformations, but the primary forms and active species of PFRs involved are not well understood. Here, we investigated the key species of PFRs of α-Fe2O3-modified biochar (MBC) and their influence on Cr(VI) reduction under anaerobic conditions simulating paddy soil environments. MBC produced bulk phenoxyl PFRs that promoted Cr(VI) reduction due to the catalytic effect of the transition metal Fe. In addition, MBC was more efficient in reducing Cr(VI) under anaerobic conditions than under aerobic conditions due to the more active and accessible dissolved PFRs present in the dissolved organic matter (DOM). The electron transfer capacity of DOM was demonstrated by excitation-emission matrix (EEM) spectrophotometry combined with parallel factor analysis, which showed that the protein-like and humic-like components of DOM were involved in Cr(VI) reduction. Furthermore, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) analysis indicated that reduced-S compounds (O/S < 4) and carboxylic acid (–COO) groups in the unsaturated aliphatic and lignin-like compounds are potentially the main active species accelerating Cr(VI) reduction under anaerobic conditions. Our results provide new insights into the role of dissolved PFRs from iron-modified biochar in promoting Cr(VI) reduction under anaerobic conditions such as flooded soils.
| • | Iron modification promoted a 5.6-fold increase in the concentration of bulk phenoxyl PFRs over unmodified biochar. |
| • | Dissolved PFRs in iron-biochar derived dissolved organic matter enhanced Cr(VI) reduction under anaerobic conditions. |
| • | Reduced sulfur compounds and carboxylic acid groups were the major reducing species in the dissolved PFRs. |
Biochar incorporation into soil has shown potential, in enhancing nitrogen fertilizer (N-fertilizer) efficacy and soil organic carbon content (SOC). This study addresses a critical gap in the literature by investigating the effects of biochar addition over a seven-year period (2014–2020) on inorganic N, SOC, and pH in Haplic Luvisol. The research involved a rain-fed field experiment, with a crop rotation comprising spring barley, maize, spring wheat, and pea. Biochar, applied at the rates of 0, 10, and 20 t ha−1 in 2014, was reapplied to specific plots in 2018. Biochar was also combined with N-fertilizer at three level (N0, N1, and N2). Results showed a significant interactive influence of biochar and N-fertilizer combination on NO3 − and NH4 + contents. Intriguingly, the addition of 10 t biochar ha−1 consistently decreased soil inorganic N levels across most of the examined months. Increasing biochar application rates led to a significant rise in pH, establishing a clear, negative correlation between soil pH and inorganic N content. Biochar significantly increased SOC compared to the control, particularly after the reapplication in 2018. However, this effect showed a diminishing trend over time. The study suggests that incorporating biochar treatments may enhance N-fertilizer effectiveness. However, the long-term implications of biochar application with N-fertilizer on N mineralization are specific to individual soil and biochar combinations. Except the application of 20 t ha−1 biochar at N2 in 2019, biochar did not affect the crop yields. Studied soil properties, including those influenced by biochar had nuanced impact on different aspects of crop yield.
| • | Biochar obtained from mixed paper fiber sludge and the grain husks resulted in a significant increase of SOC over 7 years. |
| • | Biochar aging resulted in a decrease in pH one year after its application in 2015 and 2019. |
| • | The combination of N-fertilizer with biochar caused an improvement in soil inorganic N content in 2014 and reapplication in 2018. |
Emergent plants have been remarkably effective in reducing phosphorus (P) discharge from ecological ditches; however, the treatment and recycling of these residues is a great challenge. In this study, magnetic biochars (MBs, i.e., MB-A, MB-C, and MB-T) were fabricated from three emergent plant residues (Acorus calamus L., Canna indica L., and Thalia dealbata Fraser, respectively) and modified with Fe(II)/Fe(III). Scanning electron microscopy-energy dispersive spectroscopy and X-ray diffraction spectra confirmed the successful loading of Fe3O4 and FeO(OH) onto the surfaces of the MBs. Batch adsorption experiments showed that MBs exhibited a higher P adsorption capacity than that of the raw biochars. Within the range of 0.8–43.0 mg L−1 in solution, the adsorption capacities of P by MB-A, MB-C, and MB-T were 304.6–5658.8, 314.9–6845.6, and 292.8–5590.0 mg kg−1, with adsorption efficiencies of 95.2–32.9%, 98.4–39.8%, and 91.5–32.5%, respectively. The primary mechanisms that caused P to adsorb onto the MBs were inner-sphere complexation and electrostatic attraction. Low pH conditions were more beneficial for the P adsorption of the MBs, while co-existing anions had a negative impact with the following order: HCO3 − > SO4 2− > Cl−≈NO3 −. The P-31 nuclear magnetic resonance results further demonstrated that the main adsorbed P species on the MBs was orthophosphate, followed by orthophosphate monoesters and DNA. Overall, MBs offer a resource utilization strategy for emergent plant residues and P-laden MBs are promising alternative P fertilizers.
| • | Emergent plant biochar modified with Fe(II)/Fe(III) enhanced P adsorption capacity. |
| • | Canna indica residue-derived MB exhibited the best P adsorption efficiency. |
| • | MBs promoted P adsorption mainly via inner-sphere complexation and electrostatic attraction. |
| • | P species adsorbed by MBs were mainly orthophosphate followed by orthophosphate monoesters and DNA. |
For the application of biochar in restoring pesticide-contaminated soils and minimizing the risk associated with their uptake in plants, it is crucial to understand the biochar impact on soil biological activities and dissipation and accumulation of pesticides in plant and soil systems. In this study, the effect of Mentha-distilled waste-derived biochar was investigated on chlorpyrifos and atrazine contaminated sandy loam soil. The four application rates of atrazine (2, 4, 6, and 8 mg kg−1) and chlorpyrifos (2, 4, 6, and 12 mg kg−1) and a single application rate of biochar (4%) were used in this study. The degradation of pesticides, the diversity of the bacterial community, and enzymatic activities (alkaline phosphatase, dehydrogenase, arylsulfatase, phenol oxidase, urease activity and N-acetyl glucosaminidase) were examined in soil. The uptake of two pesticides and their effect on growth and stress parameters were also investigated in plants (A. paniculata). The dissipation of chlorpyrifos and atrazine followed simple first-order kinetics with a half-life of 6.6–74.6 and 21–145 days, respectively. The presence of deisopropyl atrazine desethyl atrazine (metabolites of atrazine) and 3,5,6-trichloro-2-pyridinol (a metabolite of chlorpyrifos) was observed in soil and plant tissues. Biochar application significantly (p = 0.001) enhanced the degradation rate of chlorpyrifos and atrazine leading to the lower half-life of chlorpyrifos and atrazine in soil. A significant reduction (p = 0.001) in the uptake of chlorpyrifos and atrazine and alteration in their binding affinity and uptake rate in plant tissues was observed in biochar treatments. The incorporation of biochar improved chlorpyrifos/atrazine degrader and plant growth-promoting bacterial genera such as Balneimonas, Kaistobacter, Rubrobacter, Ammoniphilus, and Bacillus. The upregulation of functional genes associated with nucleotide, energy, carbohydrate, amino acid metabolism, xenobiotic biodegradation, and metabolism: atrazine degradation was observed in biochar treatments. The biochar amendments significantly (p = 0.001) reduced the plant’s uptake velocity (Vmax) and affinity (Km) of chlorpyrifos and atrazine. These results delineated that Mentha-distilled waste-derived biochar can potentially remediate chlorpyrifos and atrazine contaminated soils and ensure the safety of plants for consumption.
| • | Biochar amendments reduced the half-life of chlorpyrifos and atrazine in soil. |
| • | Biochar altered the binding affinity and uptake rate of chlorpyrifos and atrazine in plant tissues. |
| • | Biochar up-regulated gene assigned to xenobiotic, energy, and carbohydrate metabolism in soil. |
| • | Biochar enhanced Pseudomonas and Bacillus species in soil. |
Combined straw and straw-derived biochar input is commonly applied by farmland management in low-fertility soils. Although straw return increases soil organic matter (SOM) contents, it also primes SOM mineralization. The mechanisms by which active microorganisms mineralize SOM and the underlying factors remain unclear for such soils. To address these issues, paddy soil was amended with 13C-labeled straw, with and without biochar (BC) or ferrihydrite (Fh), and incubated for 70 days under flooded conditions. Compound-specific 13C analysis of phospholipid fatty acids (13C-PLFAs) allowed us to identify active microbial communities utilizing the 13C-labeled straw and specific groups involved in SOM mineralization. Cumulative SOM mineralization increased by 61% and 27% in soils amended with Straw + BC and Straw + Fh + BC, respectively, compared to that with straw only. The total PLFA content was independent of the straw and biochar input. However, 13C-PLFAs contents increased by 35–82% after biochar addition, reflecting accelerated microbial turnover. Compared to that in soils without biochar addition, those with biochar had an altered microbial community composition-increased amounts of 13C-labeled gram-positive bacteria (13C-Gram +) and fungi, which were the main active microorganisms mineralizing SOM. Microbial reproduction and growth were susceptible to nutrient availability. 13C-Gram + and 13C-fungi increased with Olsen P but decreased with dissolved organic carbon and contents. In conclusion, biochar acts as an electron shuttle, stimulates iron reduction, and releases organic carbon from soil minerals, which in turn increases SOM mineralization. Gram + and fungi were involved in straw decomposition in response to biochar application and responsible for SOM mineralization.
| • | Straw return accelerates microbial mineralization of SOM. |
| • | Combined biochar and straw input raises SOM mineralization by 60%. |
| • | Biochar addition increases 13C incorporation from straw into Gram + bacteria and fungi. |
| • | 13C-Gram + bacteria and 13C-fungi are the dominant active microorganisms that mineralize SOM. |
Hydrothermal carbonization (HTC) is a thermochemical conversion technology to produce hydrochar from wet biomass without drying, but it is time-consuming and expensive to experimentally determine the optimal HTC operational conditions of specific biomass to produce desired hydrochar. Therefore, a machine learning (ML) approach was used to predict and optimize hydrochar properties. Specifically, biochemical components (proteins, lipids, and carbohydrates) of biomass were predicted and analyzed first via elementary composition. Then, accurate single-biomass (no mixture) based ML multi-target models (average R 2 = 0.93 and RMSE = 2.36) were built to predict and optimize the hydrochar properties (yield, elemental composition, elemental atomic ratio, and higher heating value). Biomass composition (elemental and biochemical), proximate analyses, and HTC conditions were inputs herein. Interpretation of the model results showed that ash, temperature, and the N and C content of biomass were the most critical factors affecting the hydrochar properties, and that the relative importance of biochemical composition (25%) for the hydrochar was higher than that of operating conditions (19%). Finally, an intelligent system was constructed based on a multi-target model, verified by applying it to predict the atomic ratios (N/C, O/C, and H/C). It could also be extended to optimize hydrochar production from the HTC of single-biomass samples with experimental validation and to predict hydrochar from the co-HTC of mixed biomass samples reported in the literature. This study advances the field by integrating predictive modeling, intelligent systems, and mechanistic insights, offering a holistic approach to the precise control and optimization of hydrochar production through HTC.
| • | Biochemical components of biomass were first predicted by elemental composition. |
| • | The multi-target ML model accurately predicted hydrochar with R 2 = 0.93. |
| • | The ash, T, N, and C were the most critical factors affecting hydrochar properties. |
| • | An online intelligent system based on optimal models was posted and verified. |
The Boudouard reaction presents promising application prospects as a straightforward and efficient method for CO2 conversion. However, its advancement is hindered primarily by elevated activation energy and a diminished conversion rate. This study employed a microwave reactor with a variable frequency as the initial approach to catalyze the CO2 Boudouard reaction over biochar, with the primary objective of producing renewable CO. The study systematically investigated the influence of various variables, including the heating source, microwave frequency, microwave power, gas hourly space velocity (GHSV), and carrier gas, on the conversion of CO2 and the selectivity towards CO. The experimental findings indicate that under static conditions, with a fixed microwave frequency set at 2450 MHz and 100 W microwave power, the Boudouard reaction did not initiate. Conversely, a CO2 conversion rate of 8.8% was achieved when utilizing a microwave frequency of 4225 MHz. Under this unique frequency, further elevating the microwave power to 275 W leads to the complete conversion of CO2. Furthermore, a comparative analysis between microwave and electrical heating revealed that the CO production rate was 37.7 μmol kJ−1 for microwave heating, in stark contrast to the considerably lower rate of 0.2 μmol kJ−1 observed for electric heating. Following the reaction, the biochar retained its robust 3D skeleton structure and abundant pore configuration. Notably, the dielectric constant increased by a factor of 1.8 compared to its initial state, rendering it a promising microwave-absorbing material.
| • | A microwave reactor with a variable frequency was utilized to perform the CO2 Boudouard reaction to produce CO. |
| • | A CO2 conversion of 100% could be maintained for more than 100 min at the microwave frequency of 4225 MHz. |
| • | The CO2 conversion of microwave heating was 96.4% higher than that of conventional electric heating. |
| • | Renewable biochar served a dual purpose as both an adsorbent and raw material in this study, with the reacted biochar demonstrating efficacy as a proficient absorbing material. |
One strategy to reduce CO2 emissions from cement production is to reduce the amount of Portland cement produced by replacing it with supplementary cementitious materials (SCMs). Biochar is a potential SCM that is an eco-friendly and stable porous pyrolytic material. However, the effects of biochar addition on the performances of Portland cement composites are not fully understood. This meta-analysis investigated the impact of biochar addition on the 7- and 28-day compressive strength of Portland cement composites based on 606 paired observations. Biochar feedstock type, pyrolysis conditions, pre-treatments and modifications, biochar dosage, and curing type all influenced the compressive strength of Portland cement composites. Biochars obtained from plant-based feedstocks (except rice and hardwood) improved the 28-day compressive strength of Portland cement composites by 3–13%. Biochars produced at pyrolysis temperatures higher than 450 °C, with a heating rate of around 10 C min-1, increased the 28-day compressive strength more effectively. Furthermore, the addition of biochar with small particle sizes increased the compressive strength of Portland cement composites by 2–7% compared to those without biochar addition. Biochar dosage of < 2.5% of the binder weight enhanced both compressive strengths, and common curing methods maintained the effect of biochar addition. However, when mixing the cement, adding fine and coarse aggregates such as sand and gravel affects the concrete and mortar's compressive strength, diminishing the effect of biochar addition and making the biochar effect nonsignificant. We concluded that appropriate biochar addition could maintain or enhance the mechanical performance of Portland cement composites, and future research should explore the mechanisms of biochar effects on the performance of cement composites.
| • | Biochar effects on Portland cement composites were studied through a meta-analysis. |
| • | Effects of biochar production condition, modification and pre-treatment were studied. |
| • | The above parameters affected the compressive strength of Portland cement composites. |
| • | Biochar addition effects were dependent on batch designs of Portland cement composites. |
Bamboo biochar was modified by lignin impregnation and microwave irradiation to enhance its performance for CO2 capture. The pore structure of lignin-impregnated biochar was significantly affected by the impregnation ratio. The maximum specific surface area of 377.32 m2 g−1 and micropore volume of 0.163 cm3 g−1 were observed on the biochar with an impregnation ratio of 1:20 (mass ratio of lignin to biochar). Lignin impregnation increased the CO2 adsorption capacity of biochar up to 134.46 mg g−1. Correlation analysis confirmed the crucial role of biochar’s pore structure in adsorption. The Avrami model fitted the CO2 capture curves well. The calculation of adsorption activation energy suggested that the adsorption process was dominated by physical mechanism assisted with partial chemical mechanism. Meanwhile, Langmuir isotherm analysis indicated that lignin impregnation transformed the larger pores of biochar into more uniform micropores, thereby making the adsorption process closer to monolayer adsorption. Both the high reusability (89.79–99.06%) after 10 successive cycles and the excellent CO2 selectivity in competitive adsorption confirmed that lignin-impregnated biochar is an outstanding adsorbent for CO2 capture.
| • | Microwave energy absorbed by biochar carbonized the impregnated lignin to increase micropore structure. |
| • | CO2 uptake on lignin-impregnated biochar reached 134.46 mg g−1 and was associated with micropore, alkalinity, and temperature. |
| • | CO2 adsorption on lignin-impregnated biochar was governed by physisorption with slight chemisorption. |
| • | Lignin-impregnated biochar demonstrated excellent reusability and selectivity in CO2 capture. |
Anaerobic digestion (AD) was initially evaluated as a potential preprocessing method for preparing biomass-based carbon electrocatalysts in this study. The AD pretreatment succeeded in the structural depolymerization and nitrogen enrichment of Hybrid Pennisetum, which provided favorable conditions to achieve efficient and homogeneous nitrogen introduction due to microorganism community enrichment and provided a porous structure by degradation of the biodegradable components. The resulted biochar exhibited improved physiochemical properties including higher specific surface areas, nitrogen content and graphitization degree than that obtained from pyrolyzing raw biomass. These improvements were positively correlated with the AD time and showed to have enhanced the performance in oxygen reduction reaction and practical microbial fuel cell applications. Amongst the investigated samples, the obtained biochar pretreated by AD for 15 days exhibited the most excellent performance with an onset potential of 0.17 V (VS. saturated calomel electrode) and the maximal power density of 543.2 mW cm−2 assembled in microbial fuel cells. This study suggested applying AD as a new biological pretreatment in the preparation of biomass-based electrocatalysts, and provided a unique pathway for fabricating high-performance biochar-based catalysts by structure optimization and N-containing active sites construction via gentle biological method, thereby providing a cost-effective method to fabricate metal-free catalysts for oxygen reduction reaction.
| • | Anaerobic digestion pretreatment was conducted to assist electrocatalyst preparation. |
| • | The biological pretreatment succeeded in carbohydrates decomposition and nitrogen enrichment. |
| • | Pretreatment derived biochar significantly increased the ORR activity and microbial fuel cell performance. |
Arsenic (As) detoxification in polluted soils by iron-based materials can be mediated by the endogenous soil organic matter (SOM), nevertheless the mechanisms remain unclear. Herein, endogenous SOM in a paddy soil was substantially removed to understand its roles on As immobilization by biochar-supported zero-valent iron (ZVI/BC). The results demonstrated that ZVI/BC application significantly decreased As bioavailability by 64.2% compared with the control soil under the anaerobic condition. XPS and HR-TEM suggested As immobilization by ZVI/BC mainly invoked the formation of ternary complexes (i.e., As-Fe-SOM). However, SOM depletion compromised the efficacy of ZVI/BC for As immobilization by 289.8%. This is likely because SOM depletion increased the fulvic acid and OH− contents in soils. Besides, ZVI/BC increased the proportion of As(III) in available As fraction, but SOM depletion altered the mechanisms associated with As(V) reduction. That is, As(V) reduction resulted from the reductive capacity of ZVI in the pristine soil, but the As(V)-reducing bacteria contributed greater to As(V) reduction in the SOM-depleted soil. Additionally, SOM depletion boosted the abundances of Fe(III)- and As(V)-reducing bacteria such as Bacillus and Ammoniphilus in soils, which enhanced the dissimilatory arsenate reduction. Thus, this work highlighted the importance of SOM in the remediation of As-contaminated soils by ZVI/BC.
| • | Endogenous soil organic matter (SOM) was removed to understand its roles in arsenic (As) immobilization by ZVI/BC. |
| • | SOM depletion compromised the efficacy of ZVI/BC for As immobilization. |
| • | As(V)-reducing bacteria contributed greater to As reduction in the SOM-depleted soil. |
Fe-modified biochar (FB) and co-using Chinese milk vetch and rice straw (MR) are two effective ways for mitigating the cadmium (Cd) contamination in paddy fields in southern China. Nevertheless, the effects of FB combined with MR on Cd passivation mechanism remain unclear. In the current study, the strengthening effects of FB induced by MR were found and the mechanisms of the extracted dissolved organic matter (DOM) from the co-decomposition of MR on Cd alleviation were investigated through pot experiment and adsorption experiment. Pot experiment demonstrated that co-incorporating FB and MR decreased available Cd by 23.1% and increased iron plaque concentration by 11.8%, resulting in a 34.7% reduction in Cd concentrations in brown rice compared with addition of FB. Furthermore, co-using FB and MR improved available nutrients in the soil. The molecular characteristics of DOM derived from the decomposition of MR (DOM-MR) were analyzed by fluorescence excitation emission matrix spectroscopy-parallel factor analysis (EEM-PARAFAC) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Results showed that lignin/carboxylic-rich alicyclic molecules and protein/amino sugar were the main compounds, potentially involved in the Cd binding. Adsorption experiments revealed that the addition of DOM-MR improved the functional groups, specific surface area, and negative charges of FB, inducing the strengthening of both physisorption and chemisorption of Cd(II). The maximum adsorption capacity of Fe-modified biochar after adding DOM-MR was 634 mg g−1, 1.30 times that without the addition of DOM-MR. This study suggested that co-incorporating MR, and FB could serve as an innovative practice for simultaneous Cd remediation and soil fertilization in Cd-polluted paddy fields. It also provided valuable insights and basis that DOM-MR could optimize the performances of Fe-modified biochar and enhance its potential for Cd immobilization.
| • | Chinese milk vetch and rice straw strengthened the Cd remediation by biochar. |
| • | Soil DOM was the key influencing factor on soil Cd immobilization. |
| • | DOM optimized the properties of biochar and produced richer functional groups. |
| • | The combination of DOM and biochar had a higher specific surface area than biochar alone. |
| • | DOM strengthened the physisorption and chemisorption capacities of Cd(II) on biochar. |
Due to continuing mining activities, Cd(II) and As(III) contamination in acid mine drainage (AMD) has become a major environmental challenge. Currently, there is increasing focus on the use of biochar to mitigate AMD pollution. However, the impact of biochar on the process of Fe(II) oxidation by Acidithiobacillus ferrooxidans (A. ferrooxidans) in AMD systems has not been determined. In this study, we investigated the effects of introducing biochar and biochar-leachate on Fe(II) biooxidation by A. ferrooxidans and on the removal of Cd(II) and As(III) from an AMD system. The results showed that the biochar-leachate had a promoting effect on Fe(II) biooxidation by A. ferrooxidans. Conversely, biochar inhibited this process, and the inhibition increased with increasing biochar dose. Under both conditions (c(A. ferrooxidans) = 1.4 × 107 copies mL–1, m(FeSO4·7H2O):m(biochar) = 20:1; c(A. ferrooxidans) = 7.0 × 107 copies mL–1, m(FeSO4·7H2O):m(biochar) = 5:1), the biooxidation capacity of A. ferrooxidans was severely inhibited, with Fe(II) oxidation efficiency reaching a value of only ~ 20% after 84 h. The results confirmed that this inhibition might have occurred because a large fraction of the A. ferrooxidans present in the system adsorbed to the biochar, which weakened bacterial activity. In addition, mineral characterization analysis showed that the introduction of biochar changed the A. ferrooxidans biooxidation products from schwertmannite to jarosite, and the specific surface area increased after the minerals combined with biochar. Coprecipitation experiments of As(III) and Cd(II) showed that Cd(II) was adsorbed by the biochar over the first 12 h of reaction, with a removal efficiency of ~ 26%. As(III) was adsorbed by the generated schwertmannite over 24 h, with a removal efficiency of ~ 100%. These findings have positive implications for the removal of As(III) and Cd(II) from AMD.
| • | Biochar-leachate promoted Fe(II) biooxidation by A. ferrooxidans. |
| • | Biochar inhibited A. ferrooxidans-mediated schwertmannite formation by adsorption. |
| • | Cd(II) was adsorbed by biochar during the initial reaction stage. |
| • | As(III) was adsorbed by schwertmannite that is gradually generated in the AMD system. |
Important properties of biochar as an effective soil amendment are its high water-holding capacity (WHC) and inhibition of water evaporation. However, the mechanism and the importance of biochar properties in controlling its own WHC and bound water evaporation remain little known. In this study, wheat straw and pine sawdust biochars were pyrolyzed in N2-flow, CO2-flow, and air-limitation environments at 300–750 ℃, and a series of the produced biochars’ properties were characterized to explore the dominant controlling factors of their WHC and bound water evaporation. The results have shown that with the increasing contents of hydrogen, nitrogen, and oxygen as well as such ratios as H/C, and (O + N)/C, WHC of the biochars was also increasing while the evaporation of biochar-bound water was decreasing. With an increase in the other studied factors, such as carbon content, pH, and specific surface area (SSA), WHC of the biochars was decreasing, and the evaporation of biochar-bound water was increasing. That was connected with the fact that biochar-nitrogen was mainly in pyridinic and pyrrolic forms, while oxygen was in the form of C = O and C–O bonds. These forms of nitrogen and oxygen could be the receptors of hydrogen bonds to link to H2O molecules. Aliphatic hydrogen with a weak positive charge could be a donor of hydrogen bonds to link to H2O molecules. However, high carbon content, as well as high SSA, indicated more exposed aromatic carbon (hydrophobic sites) that could suppress the binding of H2O molecules. Additionally, high pH indicated that H2O molecules were dominated by OH–, which generated strong electrostatic repulsion with the negatively charged nitrogen- and oxygen-containing groups of biochar. It was also shown that the nitrogen-containing groups played a more important role (importance – 0.31) in WHC of the biochar than other parameters, including carbon, oxygen, hydrogen, ash contents, pH, SSA (importance from 0.02 to 0.09). Nitrogen, oxygen, and carbon contents had the most important influence on the evaporation of biochar-bound water in all studied factors. Furthermore, wheat straw biochar produced at low pyrolysis temperatures in N2 atmosphere (with high nitrogen and oxygen contents) had the highest WHC and the lowest evaporation of biochar-bound water. Consequently, it can be suggested that biochar rich in nitrogen can be an effective water retention agent and can improve agricultural soil moisture.
| • | Nitrogen-containing groups (pyridinic and pyrrolic nitrogen) played a crucial role in the improvement of biochar water-holding capacity. |
| • | Nitrogen- and oxygen-containing groups inhibited the evaporation of biochar-bound water. |
| • | Biochar rich in nitrogen and oxygen may be an effective water retention agent to maintain soil moisture. |
Pyrolysis is one method for treating sewage sludge, particularly in remote areas or decentralised systems. The end product of pyrolysis, sludge-char, can serve as a soil improver. However, there is a lack of comprehensive data on the organic pollutants’ behaviour in sludge-char. In our work, we focused on the behaviour of per- and polyfluoroalkyl substances (PFASs). Sludge was pyrolyzed at 200–700 °C to determine the minimum safe temperature for effective PFASs removal. It is important to note that PFASs may not only be mineralized but also cleaved to unanalyzed PFASs and other organofluorinated substances. To address this issue, we incorporated additional measurements of organic fluorine in the experiment using combustion ion chromatography (CIC). Due to the inherent heterogeneity of sludge, containing a variety of pollutants and their precursors, we conducted pyrolysis on artificially contaminated sand. This allowed us to assess and compare the behaviour of PFASs in a homogeneous matrix. Based on our analyses, we determined that a temperature greater than 400 °C is imperative for effective PFASs and organic fluorine removal. The results were verified by analyzing samples from a commercial sludge pyrolysis unit at the Bohuslavice-Trutnov WWTP, which confirmed our measurements. In light of these results, it becomes evident that sludge pyrolysis below 400 °C is unsuitable for PFAS removal from sewage sludge.
| • | The minimum temperature for significant PFASs and organic fluorine removal was 400 °C. |
| • | PFASs were part of primary pyrolysis gas: purification or combustion is necessary. |
| • | Contamination by PFASs and their congeners could be monitored with organic fluorine. |
The present study aimed to accelerate the humification and to investigate how MnO2 modification of biochar (MBC) drives the humus formation during composting with chicken manure. In this study, compared with the control group (CK), the addition of MBC caused an increase in the concentration of both humus and humic acid (HA), with a respective enhancement of 29.1% and 37.2%. In addition, MBC also improved the stability of compost products. Hetero two-dimensional correlation spectra further exhibited that the MBC could alter the formation mechanism of humus fractions during composting. Random forest analysis showed that Microbacterium, Bacteroides, Kroppenstedtia, Gracilibacillus, and Lentibacillus were significantly related to humus formation (P < 0.05). MBC enhanced the absolute abundance of these five genera during composting. The structural equation model further confirmed that these five genera could be indirectly involved in humus formation, through the production of aromatic compounds via secondary metabolism. Additionally, these five genera could directly transform organic components into macromolecular humus structures. Therefore, the increase in these five genera might be a direct response to the acceleration of the humification during MBC composting. These findings demonstrate the potential value of MBC in harmless disposal of hazardous biowastes through composting.
| • | MnO2 modification of biochar changed the formation mechanism of humus fractions. |
| • | Key genera involved in humus formation were identified. |
| • | Among of MnO2 modification of biochar, key genera and humus formation were revealed. |
This study investigated the effects of bamboo age, bamboo parts, and pyrolysis temperatures on the physiochemical properties of bamboo char throughout a series of pyrolysis processes spanning from 150 °C to 1000 °C. The results indicated that as the pyrolysis temperature increased from 150 °C to 500 °C, the yield of bamboo char experienced a rapid decline, settling at a maximum of 69%, with no significant impact from bamboo age and parts. Subsequently, as the pyrolysis temperature continued to rise from 500 °C to 1000 °C, the yield stabilized at 25.74–32.64%. Besides, fixed carbon (FC), volatile matter (VM), and ash content were temperature-dependent, while the H/C, O/C, (N + O)/C, and aromatic index kept constant after reaching 500 °C. Notably, 800 °C was confirmed to be a crucial turning point for physiochemical properties, at which the graphitic structural changes occurred, pore collapsed, and potassium salts released. Bamboo age was proved to enhance the stability. Pearson correlation coefficient (PCC) analysis revealed that the pyrolysis temperature was positively correlated (p < 0.01) with ash (0.76), FC (0.97), AI (0.81), R50 (0.77), and C–C/C = C/C–H (0.87). Conversely, negative correlations (p < 0.01) were observed with VM (−0.91), O/C (0.88), H/C (−0.95), (N + O)/C (−0.87), C loss (−0.79), and labile organic-C (−0.78). Additionally, bamboo age was negatively correlated (p < 0.01) with C loss (−0.40), volatile organic-C (−0.63), labile organic-C (−0.45), and recalcitrant organic-C (−0.40), but positively associated with R50 (0.54), refractory organic-C (0.42), and inorganic-C (0.52). Bamboo parts did not exhibit significant correlations with char properties.
| • | 500 °C and 800 °C served as key turning points for the properties of biochar. |
| • | Bamboo age had a positive effect on thermal stability and chemical stability. |
| • | There was no significant difference in properties between different parts (internodes and nodes) of bamboo. |
In this work, an invasive plant (Aster subulatus Michx) mesopore laminar biochar loaded with transition metal Co (CoS@MLBC) was synthesized by a one-step hydrothermal carbonization way for activating peroxymonosulfate (PMS) to remove antibiotics in water. We characterized the structure and morphology of CoS@MLBC and tested its performance. The results showed that the carbon nitride structure was formed on CoS@MLBC, which improved its adsorption capacity for antibiotics and PMS. In addition, Co-doping significantly enhanced the PMS activity and efficiently degraded ciprofloxacin (CIP) over a wide pH range. It was identified that radical and non-radical synergistic action had a critical effect on the CIP degradation process. Furthermore, CoS@MLBC could completely remove CIP within 10 min and had a high removal efficiency (98%) after four cycles. Three possible pathways of the CIP degradation process with 12 intermediates were proposed and their ecotoxicity was analyzed. This work provides a new perspective for preparing biochar from invasive plants for the degradation of antibiotics in water, realizing the concept of “treating the wastes with wastes”.
| • | A novel catalyst CoS@MLBC with the carbon nitride structure was synthesized. |
| • | ·OH, SO4 · − and 1O2 were the main active species in the ciprofloxacin degradation process. |
| • | Twelve intermediates were qualitatively determined and identified. |
Eco-friendly next-generation energy storage devices with high energy density are required to meet the increasing demand for sustainable and green electronics. However, their manufacturing requires a lot of chemical precursors and is usually accompanied by chemical waste; it also involves laborious and time-consuming processes such as mixing, heat treating, casting, and drying. Here, we proposed that mass production of microsupercapacitors (MSCs) for green electronics can be achieved by embedding manganese monoxide (MnO) on wood-derived laser-induced-graphene (LIG) via femtosecond laser direct writing (FsLDW) technique. The direct synthesis of MnO/LIG hetero-nanostructures on wood was realized by drop-casting a small amount of precursor between the first and second FsLDW. The preceding FsLDW thermochemically converted wood into LIG while the following FsLDW converted the precursor into MnO, resulting in MnO/LIG hetero-nanostructures. As-fabricated MnO/LIG MSC exhibited enhanced areal capacitance (35.54 mF cm−2 at 10 mV s−1) and capacitance retention (approximately 82.31% after 10,000 cycles) with only a small inclusion of Mn sources (0.66 mg cm−2) and short production time (10 min cm−2), which attributes to operate light-emitting diodes, digital clocks, and electronic paper as well. This approach enables the green, facile, fast, and cost-effective fabrication of future sustainable energy storage devices from biomass for next-generation green electronics.
| • | MnO/LIG based high-density energy storage devices were fabricated on natural wood. |
| • | Fabrication process was eco-friendly, which required a precursor up to 0.66 mg cm−2. |
| • | 2.50 times enhancement of areal capacitance at a current density of 1000 µA cm−2. |
| • | Microsupercapacitor synthesis time was fast up to 10 min cm−2. |
| • | It was a facile process via a femtosecond laser. |
The development of efficient and sustainable composites remains a primary objective of both research and industry. In this study, the use of biochar, an eco-friendly reinforcing material, in additive manufacturing (AM) is investigated. A high-density Polyethylene (HDPE) thermoplastic was used as the matrix, and the material extrusion (MEX) technique was applied for composite production. Biochar was produced from olive tree prunings via conventional pyrolysis at 500 °C. Composite samples were created using biochar loadings in the range of 2.0–10.0 wt. %. The 3D-printed samples were mechanically tested in accordance with international standards. Thermogravimetric analysis (TGA) and Raman spectroscopy were used to evaluate the thermal and structural properties of the composites. Scanning electron microscopy was used to examine the fractographic and morphological characteristics of the materials. The electrical/dielectric properties of HDPE/biochar composites were studied over a broad frequency range (10–2 Hz–4 MHz) at room temperature. Overall, a laborious effort with 12 different tests was implemented to fully characterize the developed composites and investigate the correlations between the different qualities. This investigation demonstrated that biochar in the MEX process can be a satisfactory reinforcement agent. Notably, compared to the control samples of pure HDPE, biochar increased the tensile strength by over 20% and flexural strength by 35.9% when added at a loading of 4.0 wt. %. The impact strength and microhardness were also significantly improved. Furthermore, the Direct current (DC) conductivity of insulating HDPE increased by five orders of magnitude at 8.0 wt. % of biochar content, suggesting a percolation threshold. These results highlight the potential of C-based composites for the use in additive manufacturing to further exploit their applicability by providing parts with improved mechanical performance and eco-friendly profiles.
| • | The reinforcement of MEX 3D printed parts with eco-friendly biochar. |
| • | Biochar was obtained from olive trees. |
| • | Popular high-density polyethylene (HDPE) was the polymeric matrix in the study. |
| • | biochar increased the tensile strength by over 20% and the flexural strength by 35.9% at a loading of 4 wt. %. |
| • | The DC conductivity of the insulating HDPE increased by five orders of magnitude at 8 wt. % biochar loading. |
Limited information is available about potential physicochemical changes that can occur in hydrochar post-production, e.g. during drying and storage. Understanding these changes is crucial not just for shaping future research plans, but also for future practical applications. Here we studied the effect of moisture (69.2% and 2.4%) and three storage temperatures (− 18, 4, and 20 °C) over a year on selected organic and inorganic compounds in hydrochar produced from the Hydrothermal carbonization (HTC) of digested cow manure. Comparison of the control wet hydrochars (WHs) and dry hydrochars (DHs) showed changes in organic compound composition due to drying. Overall, the total amount of the selected organic compounds was notably greater in WH (15.2 g kg−1 DM) compared to DH (11.8 g kg−1 DM), with variations observed in individual compound concentrations. Drying, however, had no significant influence on the identified inorganic compounds. Storage caused significant changes in both WH and DH, particularly in organic compounds after 12 weeks. Sugars (2–sevenfold), acids (36–371%), and aromatics (58–120%) in stored samples at week 52 were significantly higher than their control values. Changes in the inorganic elements (e.g., Co, K, Mg, Mn, P, S, Sr, and Zn) occurred faster in WH, with significant differences starting from week 1 compared to their control values, while DH showed fewer changes. Based on these changes in both organic and inorganic content, we recommend the optimal storage conditions for future HTC studies to preserve hydrochar properties. Finally, we discussed potential applications for stored hydrochars, with DH showing greater stability, especially at − 18 °C, making it suitable for various applications.
| • | Drying of hydrochar and storage time affected concentrations of acids, aromatics, and sugars significantly |
| • | Changes were observed at all storage temperatures—dried hydrochar stored at − 18 °C exhibited higher stability. |
| • | Recommended storage conditions could be used for upcoming HTC research and hydrochar applications. |
The regulation of the pyrolysis process is a key step in increasing the carbon sequestration capacity of biochar. The effect of K3PO4 addition on the yield, chemical composition, characteristic functional groups, macromolecular skeleton, graphite crystallites, and stability of biochar was studied in this paper using two-dimensional infrared correlation spectroscopy (2D-PCIS), X-ray photoelectron spectroscopy, Raman spectrum, and other characterization methods combined with thermal/chemical oxidation analysis. It is discovered that adding K3PO4 may effectively minimize the graphitization temperature range and increase biochar's yield, aromaticity, H/C ratio, and proportion of refractory/recalcitrant organic carbon. The 2D-PCIS and Raman analysis revealed that K3PO4 mostly promoted the dehydrogenation and polycondensation process of the aromatic rings in the char precursor, transforming the amorphous carbon structure of biochar into an ordered turbostratic microcrystalline structure. K3PO4 enhanced biochar stability mostly at medium-high temperatures (350 ~ 750℃) by stimulating the transformation of unstable structures of biochar to stable carbon-containing structures or by inhibiting the interaction of its active sites with oxidants through the mineralization process. A 20% phosphorus addition increased biochar's refractory index (R50) by roughly 11%, and it also boosted biochar's oxidation resistance (H2O2 or K2CrO4) efficiency, reducing carbon oxidation loss by up to 7.31%. However, at higher temperatures (> 750 ℃), the doping of phosphorus atoms into the carbon skeleton degraded the biochar structure's stability. The results of this study suggest that using exogenous phosphorus-containing additives is an efficient way to improve the stability of biochar.
| • | K3PO4 promoted biochar precursor's dehydrogenation/polycondensation process to form fused-ring aromatic structures. |
| • | K3PO4 increased recalcitrant carbon proportion and shielded biochar's active sites through the mineralization process. |
| • | By adding 20 wt% of K3PO4, the thermal and chemical stability of biochar were enhanced by 11% and 7%, respectively |
Biochar application can alleviate the adverse effects of saline-alkali stress on crops. However, the long-term effects of one-off biochar application on soil physicochemical properties, salt concentration, nutrient availability, soil enzyme activities, and rice yield under highly saline-alkali paddy soils remain unclear. Here, a 6-year paddy field study was conducted in a saline-alkali paddy field using two nitrogen application levels (0 and 225 kg ha−1) and four biochar application rates [0 (T0), 1.5% (T1.5), 3.0% (T3.0), and 4.5% (T4.5) biochar, w/w]. The results showed that compared with T0, the bulk density (BD) under T1.5, T3.0, and T4.5 treatments significantly decreased by 11.21%, 16.33%, and 25.57%, while total porosity (Tp) and saturated hydraulic conductivity (Ks) increased by 19.15–27.34% and 3217.78–5539.83%, respectively. Biochar consistently improved soil macro-aggregates, mean weight diameter (MWD), and the percentage of water-stable aggregates (PWSA) over the years. Additionally, one-off application of biochar continuously reduced the soil Na+ concentration, Na+/K+ ratio, Na+/Ca2+ ratio, saturated paste extract (ECe), exchangeable sodium percentage (ESP), and sodium adsorption ratio (SARe). However, it reduced the pH in 2021 and 2022 only. It enhanced the concentration of K+, Ca2+, Mg2+, and cation exchange capacity (CEC) over the 6-year study, indicating its longer-term positive impact. Furthermore, the one-off biochar application, especially under high application rate treatments (T3.0 and T4.5), significantly and continuously improved nutrient availability and soil enzyme activities. However, alkali-hydrolysable nitrogen (AN) decreased in the initial year of biochar application. The grain yield of T1.5, T3.0, and T4.5 surpassed that of T0 by 116.38%, 141.24%, and 145.20%, respectively. Notably, the rice yield reached its peak with the treatment of 3.0% (w/w) in all 6 years of study period. These findings offered new perspectives on repairing and improving soil quality and production ability of highly saline-alkali paddy soils.
| • | A long-term (6-year), one-off application of biochar was conducted in a highly saline-alkali paddy field. |
| • | Biochar consistently decreased soil BD, increased Tp, Ks, and improved soil aggregates. |
| • | Biochar showed a sustained ability to alleviate saline-alkali stress. |
| • | The continuous improvement of soil functions acted on the increase of rice yield. |
As for Atrazine (C8H14ClN5) degradation in soil, iron (Fe)-manganese (Mn) bimetallic biochar composites were proved to be more efficient for persulfate (PS) activation than monometallic ones. The atrazine removal rates of Fe/Mn loaded biochar + PS systems were 2.17–2.89 times higher than Fe/Mn loaded biochar alone. Compared with monometallic biochar, the higher atrazine removal rates by bimetallic biochar (77.2–96.7%) were mainly attributed to the synergy degradation and adsorption due to the larger amounts of metal oxides on the biochar surface. Atrazine degradation in Fe-rich biochar systems was mainly attributed to free radicals (i.e., and ·OH) through oxidative routes, whereas surface-bound radicals, 1O2, and free radicals were responsible for the degradation of atrazine in Mn-rich biochar systems. Furthermore, with a higher ratio of Fe(II) and Mn(III) formed in Fe-rich bimetallic biochar, the valence state exchange between Fe and Mn contributed significantly to the more effective activation of PS and the generation of more free radicals. The pathways of atrazine degradation in the Fe-rich bimetallic biochar systems involved alkyl hydroxylation, alkyl oxidation, dealkylation, and dechlorohydroxylation. The results indicated that bimetallic biochar composites with more Fe and less Mn are more effective for the PS-based degradation of atrazine, which guides the ration design of easily available carbon materials targeted for the efficient remediation of various organic-polluted soil.
| • | Both Fe- and Mn-rich bimetallic biochar can effectively activate persulfate, but Fe-rich biochar is superior. |
| • | Atrazine degradation in Fe-rich biochar systems was attributed to free radicals through oxidative routes. |
| • | Atrazine degradation pathways involved alkyl hydroxylation, alkyl oxidation, dealkylation, and dechlorohydroxylation. |
Production of liquid fertilizers containing nitrogenous nutrients and biostimulants from sewage sludge (SS-NB) has been attracting increasing attention due to its excellent fertilization effect and resource recycling attributes. To better understand the functional effects of nutrients and biostimulants in SS-NB on soil, the adsorption capacity and mechanism of straw biochar (SB) and wood chip biochar (WCB) for alkaline and neutral SS-NB components were investigated. The adsorption of total organic carbon (TOC) from alkaline and neutral SS-NB by WCB was 61.14% and 89.73%, respectively, higher than that by SB, which was 56.25% and 83.36%. Moreover, TOC from neutral SS-NB was more readily adsorbed, especially for fulvic and humic acids. SB had a strong adsorption capacity for calcium ions and nitrogen (TKN, nitrate N, protein, amino acid) and released large amounts of P. In addition, WCB and SB showed a strong affinity for macromolecules (proteins) and reducing substances (lignin and lipids) and excellent fixation ability for phytohormones and allelochemicals. However, WCB adsorbed more types of molecular substances than SB while maintaining a high immobilization rate. Analysis of the adsorption mechanism showed that surface amino groups of the biochar were involved in adsorption, while WCB had additionally high adsorption efficiencies through pore adsorption, hydrogen bonding adsorption and pore size-exclusion effects. The study revealed that biochar can be used as an efficient adsorption carrier for SS-NB to improve soil fertility management.
| • | SB was better able to fix N (TKN, NO3 −−N, proteins, amino acids) than WCB. |
| • | More humic acid fluorescent substances from neutral SS-NB adsorbed on biochar. |
| • | WCB and SB had excellent immobilization capacity for phytohormones and allelochemicals. |
| • | WCB had higher adsorption efficiencies for N-, P-, and S-containing molecules. |
| • | Hydrogen bonding and pore size-exclusion effect enhanced the adsorption of WCB. |
Hydrothermal carbonization (HTC) converts wet biomass into hydrochar and a process liquid, but aromatic compounds in the products have been reported as a roadblock for soil applications as they can inhibit germination, plant growth, and soil microbial activity. Here, we compared HTC and hydrothermal humification (HTH) of cow manure digestate while varying the initial alkaline content by adding KOH. HTH converted 37.5 wt% of the feedstock to artificial humic acids (A-HAs) found in both solid and liquid, twice that of HTC. HTH reduced phenolic and furanic aromatic compounds by over 70% in solids and 90% in liquids. The A-HAs in HTH resemble natural humic acids (N-HA), based on FTIR, UV–vis spectra, and CHN and XRD analysis. The HTH liquid possesses 60% higher total organic carbon (TOC) than HTC. Although one-third of TOC can be precipitated as A-HA, a high TOC concentration remains in the liquid, which is shown to be mainly organic acids. Therefore, we also evaluated the HTC and HTH liquids for anaerobic biomethane production, and found that compared to the original cow manure digestate, the HTH liquids increased methane yield by 110.3 to 158.6%, a significant enhancement relative to the 17.2% increase seen with HTC liquid. The strong reduction in organic acids during biogas production from HTH liquid indicates the potential for converting soluble byproducts into methane, while maintaining high A-HAs levels in the solid product.
| • | Hydrothermal humification of the digestate feedstock created about 37.5 wt% artificial humic acids in both solid and liquid phases. |
| • | Increasing the alkaline content of the reaction media significantly decreased the aromatic content in the process liquid while increasing the concentration of organic acids and sugars. |
| • | There was little to no gas production observed in the HTH process at higher alkaline contents, indicating carbon preservation in the liquid and solid phases. |
| • | Anaerobic processing of the hydrothermal humification (HTH) process liquid resulted in a 158.6% increase in methane production compared to the primary biomass. |
| • | The organic acid concentrations decreased after the anaerobic fermentation, while the main HTH product, artificial humic acids, remained nearly unchanged. |
Cd contamination, especially in farmland soil, can pose serious threats to human health as well as ecological security. Stabilization is an important strategy for agricultural soil Cd remediation. In this study, a Cd-resistant strain (Cupriavidus B-7) was isolated and loaded onto cow manure (CDB), rice straw (RSB) and pine wood biochar (PB) to investigate its effects on Cd stabilization by a 60-day pot experiment. Results indicated that the Cupriavidus B-7-loaded biochar (labelled as CDBB, PBB and RSBB) reduced the CaCl2-extractable Cd by 43.06–59.78%, which was significantly superior to individual applications of Cupriavidus B-7 and biochar. Likewise, the soil physicochemical properties, urease, catalase and phosphatase activities were improved, indicating improved soil health. Consequently, dry weights of pakchoi’s shoot and root were increased by 938.9–1230.9% and 149.1–281.2%, respectively, by applying CDBB, PBB and RSBB. Meanwhile, the Cd accumulation in pakchoi shoots decreased by 38.06–50.75%. Notably, the RSBB exhibited an optimal performance on pakchoi growth promotion and Cd accumulation alleviation. The structural equation model indicated the synergistic effect on pakchoi growth promotion and Cd accumulation decreased between biochar and Cupriavidus B-7. Our research provides some new insights into the development of strategies for green and sustainable remediation of Cd-contaminated soil.
| • | A Cd resistant Cupriavidus B-7 (B-7) was isolated from copper mining soil |
| • | Biochar, B-7 and their conbination were used to remediate Cd polluted soil |
| • | Biochar loaded B-7 outperformed individual treatments for Cd stabilization |
| • | Biochar loaded B-7 alleivated the Cd uptake and promoted pakchoi growth |
In this study, a newly developed composite of biochar-poly(m-phenylenediamine) (BC-PmPD) exhibiting a distinct skeletal structure was synthesized for the purpose of extracting Cr(VI) from aqueous solutions. BC was employed as a supportive carrier onto which PmPD nanoparticles were uniformly affixed through in-situ polymerization and oxidation synthesis, both within and outside the layered configuration of BC. The structural stability and morphologies of BC-PmPD were assessed utilizing Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, thermogravimetric analysis, analysis of specific surface area and pore size, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. In comparison to other modified BCs reported, BC-PmPD exhibited the highest Cr(VI) removal rate. Specifically, at 303 K, BC-PmPD achieved a maximum Cr(VI) removal capacity of 775 mg g−1, surpassing the capabilities of unmodified BC and PmPD by 10.4 and 2.13 times, respectively. Analyses involving XPS, FTIR, and density functional theory calculation confirmed that proton transfer happened between protonated amine (−NH2) functional group within the structure of BC-PmPD and HCrO4 − before the formation of hydrogen bond. Subsequently, environmentally persistent free radicals facilitated the reduction of the adsorbed Cr(VI). Quantification of the functional groups indicated that the amino group was responsible for 93.0% of the Cr(VI) adsorption in BC-PmPD. BC-PmPD displayed potent adsorption and reduction capabilities, alongside notable stability, repeatability, and promising potential for application in the remediation for high concentrations of Cr(VI) in electroplating wastewater scenarios.
| • | Novel 3D material was prepared and the removal rate of Cr(VI) on BC-PmPD was the highest as compared to reported BCs. |
| • | The maximum adsorption amount of Cr(VI) on BC-PmPD was high up to 1034 mg g−1 at 323 K and −NH2 adsorbed 93.0% HCrO4 –. |
| • | DFT calculation confirmed proton transfer happened between protonated −NH2 and HCrO4 − before the formation of H bond. |
The incomplete combustion of biomass and fossil fuels results in the formation of not only black carbon (BC) but also black nitrogen (BN), the dissolved fractions of which (i.e., DBC and DBN) are important components of dissolved organic matter pool. Relative to DBC, the activity and reactivity of DBN are much less understood. Here, we investigated the catalytic effect of DBN derived from N-enriched biomass in the abiotic transformation of chlorophenols by sulfides. The medium-temperature DBN (450 °C) exhibited 13–144% higher catalytic efficiency than other DBN samples and 9.3 times higher than its DBC counterpart. Both electron paramagnetic resonance spectra and fluorescent probe technique indicated that the attached sulfides contributed to the formation of reactive oxygen species (ROS) as the “primary” radicals by favoring electron transfer from DBN to chemisorbed oxygen, and then the generated ROS reacted with N-oxides in DBN to form reactive nitrogen species (RNS) as the “secondary” radicals. The contribution of RNS to the decay of 2-chlorophenol by DBN450 was up to 72%, much higher than that of ROS and non-radical mechanism. These findings suggest that the catalytic effect of DBN is distinct but no less significant than that of DBC to the abiotic transformation of micropollutants in water/soil systems.
| • | Dissolved black nitrogen is an overlooked active nano-catalyst in the natural environment. |
| • | The medium-temperature dissolved black nitrogen exhibited the highest catalytic efficiency. |
| • | Not only ROS but also RNS were generated in the dissolved black nitrogen-sulfide system. |
| • | The contribution of RNS to the decay of 2-CP was higher than that of ROS and non-radical mechanism. |
Biochar is widely used for sediment remediation owing to its excellent adsorption properties and low carbon footprint. However, the impacts of biochar capping on phosphorus (P) bioavailability and mobility in the sediment are little known. In this study, the P mobilization processes in sediments capped with biochar were investigated by combining advanced high-resolution sampling techniques and microbiome analysis. The results showed that biochar is a double-edged sword for the sediment P release, depending on the application dosage and the capping time. In the short term (30 days), 2-cm biochar capping decreased the release flux of soluble reactive phosphorus (SRP) by 73.1%, whereas the 1-cm biochar capping significantly increased the release flux of SRP by 51.0%. After aging of biochar (80 days), the resupply capacity of sediment P was improved, resulting in increases of more than 33.7% and 121.5% in the release fluxes of SRP in the 1-cm and 2-cm capping groups, respectively, compared to the control group. Chemisorption played a pivotal role in regulating the levels of SRP, particularly during the short-term capping period. And more biochar can provide more adsorption sites on P. The P mobilization increase could be attributed to P desorption from biochar after biochar aging. Furthermore, biochar capping intensified the microbial-mediated iron reduction and organic matter decomposition, which enhanced P mobility. Our study highlights the importance of biochar application dosage and the capping time in sediment remediation, providing a scientific basis for the optimization of biochar capping techniques.
| • | Biochar capping caused a sudden increase in organic matter and P concentration. |
| • | Aging biochar enhanced the bioavailability and release flux of P. |
| • | Biochar capping enhanced the P mobility by altering the microbial community. |
To prevent the spread of pine wilt disease (PWD), a transportable carbonization equipment was designed for in-situ treatment of infected pine wood (IPW). The equipment killed all pine wood nematodes (PWNs) in IPW when carbonization temperature was up to 200 °C. The optimal laboratory process of infected pine wood charcoal (IPWC) was carbonization temperature of 500 °C, heating rate of 3 °C min−1 and holding time of 0 min. Based on the optimal laboratory process, the transportable carbonization equipment produced IPWC with a fixed carbon content of 79.82%, and ash content of 1.14% and a moisture content of 7.83%, which meets the requirements of EN 1860-2:2005(E) standard. The economic efficiency of incineration (T1 mode), crushing (T2 mode), and transportable carbonization (T3 mode) was evaluated. For each ton of IPW treatment, the profit generated was −75.48 USD in T1 mode, 26.28 USD in T2 mode, and 51.91 USD in T3 mode. T3 mode had the highest economic efficiency. These findings will be helpful to provide guidance for the control of PWD and value-added utilization of IPW.
| • | A transportable carbonization equipment was designed for in-situ treatment of IPWs |
| • | The transportable carbonization equipment killed all PWNs of IPW when carbonization temperature was up to 200 °C. |
| • | In the transportable carbonization mode, the income generated from treating each ton of IPW was 51.91 USD. |
Although addition of pyrolyzed organic materials (biochars) to soil generally results in increased growth and physiological performance of plants, neutral and negative responses have also commonly been detected. Toxicity of organic compounds generated during pyrolysis, sorbed by biochars, and then released into the soil solution, has been implicated as a possible mechanism for such negative effects. Conversely, water-soluble biochar constituents have also been suggested to have “hormetic” effects (positive effects on plants at low concentrations); however, no specific compounds responsible have been identified. We investigated the relative phytotoxicity—and possible hormetic effects—of 14 organic compounds common in aqueous extracts of freshly produced lignocellulosic biochars, using seed germination bioassays. Of the compounds examined, volatile fatty acids (VFAs: acetic, propionic, butyric, valeric, caproic, and 2-ethylbutyric acids) and phenol, showed acute phytotoxicity, with germination-based ED50 values of 1–30 mmol L−1, and 2-ethylbutyric acid showed ED50 values of 0.1–1.0 mmol L−1. Other compounds (benzene, benzoic acid, butanone, methyl salicylate, toluene, and 2,4-di-tert-butylphenol) showed toxic effects only at high concentrations close to solubility limits. Although phytotoxic at high concentrations, valeric and caproic acid also showed detectable hormetic effects on seedlings, increasing radicle extension by 5–15% at concentrations of ~ 0.01–0.1 mmol L−1. These data support the hypothesis that VFAs are the main agents responsible for phytotoxic effects of lignocellulosic biochar leachates, but that certain VFAs also have hormetic effects at low concentrations and may contribute to positive effects of biochar leachates on early plant development in some cases.
| • | 151 compounds were identified in leachates from 13 biochars. |
| • | Among common compounds, volatile fatty acids (VFAs) and phenol showed the most pronounced phytotoxic effects. |
| • | Some VFAs also had hormetic effects, enhancing radicle extension growth at low concentrations. |
| • | Effects were consistent among test plant species but the smallest-seeded species showed the highest sensitivity. |
The response of soil microorganisms and plants in soil ecosystems to biochar is well recognised. However, biochars’ impact on large soil animal, such as ants, is inadequately understood, with only limited studies focusing on the abundance and mortality rates of some specific ant species. In this study, soil physicochemical properties, and ant community diversity and functional characteristics were compared between experimental plots with and without biochar application. No significant differences in soil (soil physicochemical properties) or ants (ant community richness, species abundance, and morphological characteristics) were observed between the two plots before biochar application. However, the biochar-treated plot soil surface temperatures, pH, and soil water content were significantly higher after 48 weeks. Biochar application promoted Cardiocondyla nuda (by 426%) and Formica japonica abundance (by 93%), but decreased Solenopsis invicta invasive ant species richness (by 54%), consistent with the fact that changes in soil properties were more beneficial to the former two species. In addition, in biochar-treated plots, F. japonica and S. invicta generally showed larger body size (18% and 6.7%), larger eyes (2.7% and 4.0%), and longer femurs (6.3% and 7.9%), which enabled them to respond better to potential barriers, such as plants. Our results highlighted that, besides species abundance and community structure, certain ant functional morphological indicators were also informative in evaluating biochar ecological implications.
| • | Biochar application enhanced soil temperature, pH, and water content. |
| • | Ants showed larger body size, larger eyes, and longer femurs with biochar application. |
| • | Biochar promoted ant richness by creating ant-preferred habitats. |
As promising energy-storage devices, zinc–air batteries (ZABs) exhibit slow reaction kinetics for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurring at their electrodes. High-performance bifunctional catalysts must thus be synthesized to accelerate the reversible conversion of oxygen and improve the rate and overall performance of ZABs. Herein, we reported the promising prospects of self-supported composite electrodes composed of wood-derived carbon (WDC) and bimetallic cobalt-iron alloys/oxides (CoFe-CoFe2O4@WDC) as efficient electrocatalysts for alkaline ORR/OER. WDC provided a favorable three-phase interface for heterogeneous reactions owing to its layered porous structure and genetic stability, thereby enabling mass diffusion and improving reaction kinetics. The CoFe2O4 spinel surface was reduced to bimetallic CoFe alloy to form abundant heterostructure interfaces that promote electron transfer. Under alkaline conditions, the optimized composite electrode exhibited a remarkable high half-wave potential of 0.85 V and an exceptionally low overpotential of 1.49 V. It also exhibited stable performance over an impressive 2340 cycles in a ZAB. Theoretical calculations also confirmed that the heterointerface addresses the issue of proton scarcity throughout the reaction and actively facilitates the creation of O–O bonds during the reversible transformation of oxygen. This study introduces a new concept for developing bifunctional and efficient electrocatalysts based on charcoal and encourages the sustainable and high-value use of forest biomass resources.
| • | Water dissociation was regulated to provide proton for smooth response under alkaline conditions and accelerate the conversion of *O2 to *OOH. |
| • | The alloy surface formed CoFe oxyhydroxide in the OER voltage range, and the adsorption capacity of intermediates was adjusted to facilitate O–O bond formation. |
| • | The d-band center moved downward due to interface electron interaction, modifying the binding ability of intermediates. |
Biochar-based sulfidized nano-sized zero-valent iron (SNZVI/BC) can effectively immobilize cadmium (Cd) in contaminated paddy soils. However, the synergistic effects between biochar and SNZVI on Cd immobilization, as well as the underlying mechanisms remain unclear. Herein, a soil microcosm incubation experiment was performed to investigate the immobilization performance of SNZVI/BC towards Cd in the contaminated paddy soil. Results indicated that the addition of SNZVI/BC at a dosage of 3% significantly lessened the concentration of available Cd in the contaminated soil from 14.9 (without addition) to 9.9 mg kg−1 with an immobilization efficiency of 33.3%, indicating a synergistic effect. The sequential extraction results indicated that the proportion of the residual Cd in the contaminated soil increased from 8.1 to 10.3%, manifesting the transformation of the unstable Cd fractions to the steadier specie after application of SNZVI/BC. Also, the addition of SNZVI/BC increased soil pH, organic matter, and dissolved organic carbon, which significantly altered the bacterial community in the soil, enriching the relative abundances of functional microbes (e.g., Bacillus, Clostridium, and Desulfosporosinus). These functional microorganisms further facilitated the generation of ammonium, nitrate, and ferrous iron in the contaminated paddy soil, enhancing nutrients’ availability. The direct interaction between SNZVI/BC and Cd2+, the altered soil physicochemical properties, and the responded bacterial community played important roles in Cd immobilization in the contaminated soil. Overall, the biochar-based SNZVI is a promising candidate for the effective immobilization of Cd and the improvement of nutrients’ availability in the contaminated paddy soil.
| • | Biochar-based sulfidized nano-sized zero-valent iron (SNZVI/BC) synergistically immobilized Cd in the contaminated soil. |
| • | SNZVI/BC effectively enhanced nutrients’ availability in the contaminated soil. |
| • | Nitrate-, Iron-, and sulfate-reducing bacteria were enriched in the SNZVI/BC-treated soil. |
| • | Precipitation and complexation played an important role in the immobilization of Cd. |
Biochar can potentially reduce heavy metals (HMs) mobility and bioavailability during composting. However, siderophores secreted by functional microbes might lead to the re-mobilization of metals like Cu and Zn. Therefore, this study intended to explore the impacts of Mikania micrantha Kunth (MM) and MM-derived biochar (MMB) in the reduction of Cu and Zn bioavailability, and siderophore-related gene abundances during composting. Compared with MM and corn straw (CS) composts, a significant decline was noticed in the extractable and reducible Cu [(2.3 mg kg−1 + 12.1 mg kg−1), and (3.3 mg kg−1 + 14.6 mg kg−1)], and Zn [(103.1 mg kg−1 + 110.1 mg kg−1), and (109.6 mg kg−1 + 117.2 mg kg−1)] in MMB and corn straw biochar (CSB) composts, respectively. Besides, the lowest relative abundance of HMs-resistant bacteria particularly Corynebacterium (0.40%), Pseudomonas (0.46%), and Enterobacter (0.47%), was noted in MMB compost. Also, a significant increase in sesquiterpenoid and triterpenoid biosynthesis abundance (5.77%) accompanied by a reduction in the abundance of clusters related to siderophore transport, and siderophore transmembrane transporter activity was detected in MMB compost. Multivariate analysis labeled temperature, moisture content, total organic carbon, Corynebacterium, and Bacillus as the primary factors significantly correlated with the Cu and Zn bioavailability (− 0.90 ≤ r ≤ 0.90, P < 0.05). The structural equation model revealed that physicochemical parameters, microbial abundance, and siderophores exert a substantial influence on Cu and Zn bioavailability. Accordingly, MM and its derived biochar are recommended as an effective approach for accelerating Cu and Zn bioavailability reduction and managing the growth and distribution of invasive plants.
| • | Biochar enhances compost physicochemical parameters and Zn and Cu immobilization. |
| • | Combined biochar and Mikania micrantha Kunth reduced Zn and Cu bioavailability. |
| • | Proteobacteria is the main phylum involving metal-resistant bacteria. |
| • | Mikania micrantha Kunth-related phytochemicals shape siderophore-related genes. |
| • | Mikania micrantha-derived biochar is a cheap, and efficient absorption additive. |
Fe–Mn oxide modified biochar (FMBC) was produced to explore its potential for remediation of Hg–Cd contaminated paddy soils. The results showed that the application of FMBC decreased the contents of bioavailable Hg and Cd by 41.49–81.85% and 19.47–33.02% in contrast to CK, while the amount of labile organic carbon (C) fractions and C-pool management index (CPMI) was increased under BC and FMBC treated soils, indicating the enhancement of soil C storage and nutrient cycling function. Dry weight of different parts of Oryza sativa L. was enhanced after the addition of BC and FMBC, and the contents of Fe and Mn in root iron–manganese plaques (IMP) were 1.46–2.06 and 6.72–19.35 times higher than those of the control groups. Hg and Cd contents in brown rice under the FMBC treatments were significantly reduced by 18.32–71.16% and 59.52–72.11% compared with the control. FMBC addition altered the composition and metabolism function of soil bacterial communities, especially increasing the abundance of keystone phyla, including Firmicutes, Proteobacteria and Actinobacteria. Partial least squares path modelling (PLSPM) revealed that the contents of Na2S2O3–Hg, DTPA–Cd and IMP were the key indicators affecting Hg and Cd accumulation in rice grains. These results demonstrate the simultaneous value of FMBC in remediation of Hg and Cd combined pollution and restoring soil fertility and biological productivity.
| • | FMBC effectively remediated Hg and Cd co-contaminated paddy soils. |
| • | FMBC increased soil labile C fractions and C sequestration. |
| • | FMBC improved the relative abundance of specific phyla and metabolism potential. |
| • | PLSPM exhibited the main ways of reducing Hg and Cd accumulation in rice grains. |
The residue of atrazine in field soils poses a major threat to crop growth in the rotation system, raising concerns about grain security and food safety. Current agricultural production requires more efficient and cost-effective mitigation measures in response to the emerging threat. This study reported the critical concentration (0.1 mg L−1) of atrazine injury to soybean seedlings in soil pore water and how biochar amendment could influence the distribution of atrazine in different soil environments. The results showed that biochar significantly reduced the concentration of atrazine in soil pore water, for example, 0.5% biochar in red (cinnamon, fluvo-aquic, paddy, black) soil reduced atrazine concentration from 0.31 (0.20, 0.18, 0.12, 0.03) mg L−1 to 0.004 (0.002, 0.005, 0.013, 0.011) mg L−1 in pore water (P < 0.01). On the basis of these, a reliable mathematical model was developed to predict the atrazine concentration in soil pore water under (or without) biochar amendment conditions. The verification results showed that the mean absolute percentage error of the model was 14.1%, indicating that the prediction error was within a reasonable range. Our work provides a precise solution to crop injury caused by soil residual herbicides with the aid of biochar, which reduces the bioavailability of atrazine in soybean seedlings. This method not only maximizes the use of biochar but also provides effective crop protection and environmental benefits.
| • | The critical value of atrazine injury to soybean seedlings in soil pore water was 0.1 mg L−1. |
| • | Biochar amendment significantly reduced the concentration of atrazine in soil pore water. |
| • | The distribution of atrazine in soil pore water can be predicted by a mathematical model. |
Thallium (Tl), vanadium (V) and arsenic (As) are considered as typical toxic elements of increased interest. Their accumulation in soils can pose a substantial health threat to human beings. In this study, Fe–Mn modified biochar (FMBC) was chemically constructed to immobilize Tl, V and As in contaminated soils. The results showed that compared with pristine biochar (BC), FMBC can achieve significantly higher passivation effects for the studied contaminated soils, which reduced the bioavailable Tl, V and As contents by 83.9%, 71.09% and 71.92%, respectively. The passivation of Tl, As, and V via FMBC application was partially attributed to a notable increase in pH, which enhances the availability of adsorptive sites. Further, the newly formed minerals, including cancrinite, gibbsite and Fe–Mn (hydr)oxides, serve as additional adsorbents, substantially reducing the mobility of Tl, V and As. Additionally, the oxidation of Tl(I) to Tl(III) by the Fe–Mn (hydr)oxide of FMBC significantly enhanced Tl immobilization, consequently diminishing its bioavailability. The findings suggest that significant environmental threats could be alleviated through the potential application of FMBC in treating Tl-As-V dominated contamination in soils, providing a new perspective for the sustainable utilization of industrially polluted soils.
| • | FMBC effectively reduced the bioavailability of Tl, As and V in contaminated soils. |
| • | Formation of new minerals during passivation can enhance adsorption of the studied elements. |
| • | Effective immobilization of Tl may be mainly ascribed to oxidation of Tl(I) to Tl(III) by FMBC. |
Anaerobic digestion technology, effective for sustainable waste management and renewable energy, but challenged by slow reaction rates and low biogas yields, could benefit from advancements in magnetic nanomaterials. This review explores the potential of magnetic nanomaterials, particularly magnetic biochar nanocomposites, to address these challenges by serving as electron conduits and providing essential iron. This review contributes a thorough overview of the application of magnetic nanoparticles loaded into biochar in anaerobic digestion and engages in a comprehensive discussion regarding the synthesis methods and characterization of various magnetic nanoparticles, elucidating their mechanisms of action in both the absence and presence of magnetic fields. Our review underscores the predominance of co-precipitation (53%) and commercially sourced nanoparticles (29%) as the main synthesis methods, with chemical reduction, pyrolysis, and green synthesis pathways less commonly utilized (8%, 5%, and 5%, respectively). Notably, pyrolysis is predominantly employed for synthesizing magnetic biochar nanocomposites, reflecting its prevalence in 100% of cases for this specific application. By offering a critical evaluation of the current state of knowledge and discussing the challenges and future directions for research in this field, this review can help researchers and practitioners better understand the potential of magnetic biochar nanocomposites for enhancing anaerobic digestion performance and ultimately advancing sustainable waste management and renewable energy production.
| • | Critical insights into using magnetic nanoparticles within biochar as a solution to sustainable waste management. |
| • | Fe3O4, nZVI, and Fe2O3 are prevalent in enhancing anaerobic digestion processes. |
| • | Insights offered on nanoparticle utilization, magnetic field impacts, and sustainable solutions integrating biochar. |
Hydrothermal carbonization (HTC) has been regarded as a promising technique for turning wet biomass into hydrochar due to its low energy consumption, low exhaust gas emissions, etc. In addition, hydrochar is an important source of dissolved organic matter (DOM), which plays a crucial part in the migration and destiny of pollutants in the environmental medium. However, there are limited studies that focus on the factors that influence the formation of DOM in hydrochar, such as hydrothermal temperature. Therefore, the current study comprehensively characterized the optical properties of DOM within hydrochar derived from sawdust (HDOM) under different hydrothermal temperatures (150–300 °C) by Ultraviolet–visible (UV–Vis) and fluorescence spectroscopy, as well as its complexation characteristic with Cu(II). The findings revealed that the organic carbon content of HDOM reached a peak of 37.3 mg L−1 when the temperature rose to 240 °C and then decreased as the temperature increased. UV–Vis spectroscopy analysis showed that the absorption capacity of HDOM at 275 nm increases with temperature and reaches a maximum value at 240 °C, indicating that high temperature promotes the formation of monocyclic aromatic compounds. High temperature enhances the aromaticity, hydrophobicity, and humification degree of HDOM, thus improving its stability and aromaticity. The E3/E4 ratios are all greater than 3.5, confirming that the main component of HDOM is fulvic acid, which corresponds to 3D-EEM and Pearson's correlation coefficient analysis. The humification index (HIX) of HDOM increased with the rise in hydrothermal temperature (150–240 °C), as observed by the three-dimensional excitation-emission matrix spectroscopy (3D-EEMs). After reaching its peak at 240 °C, the HIX value gradually dropped in line with the trend of the DOC change. Moreover, the bioavailability (BIX) value of DOM was all high and greater than 1, indicating all the HDOM are readily bioavailable. Two microbial humic substances (C1 and C4), a humic-like substance (C2), and a protein-like substance (C3) were discovered in DOM by integrating 3D-EEMs with parallel factor analysis (PARAFAC). Their fluorescence intensity decreases as the Cu(II) concentration increases, indicating the formation of complexes with Cu(II). As the temperature rises, the binding ability of DOM and Cu(II) changes significantly, reaching the optimum at 300 °C. Meanwhile, the substance C2 has the strongest binding ability with Cu(II). This research emphasizes the significance of spectroscopy analysis in determining the evolution of hydrochar-derived DOM, the potential for heavy metal binding and migration, and its characteristics and features.
| 1. | The effect of temperature on the spectral properties of hydrochar-derived DOM was studied. |
| 2. | The aromaticity and humification degree of HDOM were enhanced by the increase in hydrothermal temperature, which enhanced the stability of hydrochar. |
| 3. | Fulvic acid and protein-like material were the dominant component, and the humic-like component (C2) had the highest binding capacity with Cu(II). |
Microalgae technology is a viable solution for environmental conservation (carbon capture and wastewater treatment) and energy production. However, the nutrient cost, slow-kinetics, and low biosorption capacity of microalgae hindered its application. To overcome them, algal-biochar (BC) can be integrated with microalgae to treat textile wastewater (TWW) due to its low cost, its ability to rapidly adsorb pollutants, and its ability to serve as a nutrient source for microalgal-growth to capture CO2 and biodiesel production. Chlorella vulgaris (CV) and algal-BC were combined in this work to assess microalgal growth, carbon capture, TWW bioremediation, and biodiesel production. Results showed the highest optical density (3.70 ± 0.07 OD680), biomass productivity (42.31 ± 0.50 mg L−1 d−1), and dry weight biomass production (255.11 ± 6.01 mg L−1) in an integrated system of CV-BC-TWW by capturing atmospheric CO2 (77.57 ± 2.52 mg L−1 d−1). More than 99% bioremediation (removal of MB-pollutant, COD, nitrates, and phosphates) of TWW was achieved in CV-BC-TWW system due to biosorption and biodegradation processes. The addition of algal-BC and CV microalgae to TWW not only enhanced the algal growth but also increased the bioremediation of TWW and biodiesel content. The highest fatty acid methylesters (biodiesel) were also produced, up to 76.79 ± 2.01 mg g−1 from CV-BC-TWW cultivated-biomass. Biodiesel’s oxidative stability and low-temperature characteristics are enhanced by the presence of palmitoleic (C16:1) and linolenic (C18:3) acids. Hence, this study revealed that the integration of algal-biochar, as a biosorbent and source of nutrients, with living-microalgae offers an efficient, economical, and sustainable approach for microalgae growth, CO2 fixation, TWW treatment, and biodiesel production.
The impact of biochar application on plant performance under drought stress necessitates a comprehensive understanding of biochar–soil interaction, root growth, and plant physiological processes. Therefore, pot experiments were conducted to assess the effects of biochar on plant responses to drought stress at the seedling stage. Two contrasting maize genotypes (drought-sensitive KN5585 vs. -tolerant Mo17) were subjected to biochar application under drought stress conditions. The results indicated that biochar application decreased soil exchangeable Na+ and Ca2+ contents while increased soil exchangeable K+ content (2.7-fold) and electrical conductivity (4.0-fold), resulting in an elevated leaf sap K+ concentration in both maize genotypes. The elevated K+ concentration with biochar application increased root apoplastic pH in the drought-sensitive KN5585, but not in the drought-tolerant Mo17, which stimulated the activation of H+-ATPase and H+ efflux in KN5585 roots. Apoplast alkalinization of the drought-sensitive KN5585 resulting from biochar application further inhibited root growth by 30.7%, contributing to an improvement in water potential, a reduction in levels of O2 –, H2O2, T-AOC, SOD, and POD, as well as the down-regulation of genes associated with drought resistance in KN5585 roots. In contrast, biochar application increased leaf sap osmolality and provided osmotic protection for the drought-tolerant Mo17, which was associated with trehalose accumulation in Mo17 roots. Biochar application improved sucrose utilization and circadian rhythm of Mo17 roots, and increased fresh weight under drought stress. This study suggests that biochar application has the potential to enhance plant drought tolerance, which is achieved through the inhibition of root growth in sensitive plants and the enhancement of osmotic protection in tolerant plants, respectively.
| • | Biochar application decreased soil exchangeable Na+ and Ca2+, but increased soil exchangeable K+ and electrical conductivity. |
| • | Biochar increased apoplastic pH, but reduced root growth, stress damage and stress response during drought for the drought-sensitive KN5585. |
| • | Biochar improved osmotic protection, trehalose accumulation, and fresh weight during drought for the drought-tolerant Mo17. |
The use of beach-cast macroalgae as a fertilizer (F) or soil amendment (SA) is coming back into focus, due to its highly efficient transformation of CO2, nutrients, salts and minerals from its aqueous surroundings into biomass. This research studied the hydrothermal carbonization (HTC) of Fucus vesiculosus macroalgae to hydrochar and evaluated its feasibility for use in soil applications. F. vesiculosus was submitted to HTC following a full factorial design of experiments with three HTC process parameters varied to assess their impact on the hydrochars: temperature (T: 160, 190, 220 °C), solid content (%So: 20, 35%), and process water recirculation (PWrec: yes and no). In general, F. vesiculosus and its hydrochars were rich in nutrients, but also contained regulated heavy metals. Investigation of the partitioning behavior of inorganic elements between the hydrochars and process water showed that heavy metals like Cr, Pb, Co and Cu tended to accumulate in the hydrochar, unaffected by HTC conditions. Nutrients such as P, N, B, and Mn were primarily found in the hydrochar and could be partially influenced to transfer to process water by changing %So and T. The correlation between the mass fractions of 22 elements in the hydrochar and HTC process parameters was studied. T was the most influential parameter, showing a significant positive correlation for eleven elements. %So and PWrec showed inconsistent effects on different elements. When process water was recirculated, some elements decreased (Ca, Cd, Fe) while others increased (K, Na, B, N) in the hydrochar. Assessment against various regulations and standards for F and SA revealed that F. vesiculosus complied with Cd limit values for most rules including the EURF and B, and was regulated only in the RAL for SA, over the limit value. In contrast, the limit value of Cd for both F and SA applications was surpassed in the 13 hydrochars. The contents of N, P, K, S, and Na in the feedstock and hydrochars complied with European F and SA rules, while they were too high for German rules on SA. The other limits for F rules were achieved (under certain HTC process parameters) except for P (lower than the requirements in F for F. vesiculosus and its hydrochars).
| • | The brown algae complied with most limit values for Cd content to be applied as soil amendment or as fertilizer. |
| • | Hydrochars from brown algae did not comply with any Cd limit values. No HTC process condition reduced the Cd content to comply with the requirements. |
| • | Inorganic mass fractions were mostly influenced by temperature (positively correlated with 11/22 elements), followed by water recirculation (7) and solid content (6). |
| • | Heavy metals accumulate in hydrochars across all HTC conditions. The partitioning for some elements (e.g., Cd, Co, Cu, W, V) showed no correlation with process conditions. |
Despite fertilization efforts, phosphorus (P) availability in soils remains a major constraint to global plant productivity. Soil incorporation of biochar could promote soil P availability but its effects remain uncertain. To attain further improvements in soil P availability with biochar, we developed, characterized, and evaluated magnesium-oxide (MgO) and sepiolite (Mg4Si6O15(OH)2·6H2O)-functionalized biochars with optimized P retention/release capacity. Field-based application of these biochars for improving P availability and their mechanisms during three growth stages of maize was investigated. We further leveraged next-generation sequencing to unravel their impacts on the plant growth-stage shifts in soil functional genes regulating P availability. Results showed insignificant variation in P availability between single super phosphate fertilization (F) and its combination with raw biochar (BF). However, the occurrence of Mg-bound minerals on the optimized biochars’ surface adjusted its surface charges and properties and improved the retention and slow release of inorganic P. Compared to BF, available P (AP) was 26.5% and 19.1% higher during the 12-leaf stage and blister stage, respectively, under MgO-optimized biochar + F treatment (MgOBF), and 15.5% higher under sepiolite-biochar + F (SBF) during maize physiological maturity. Cumulatively, AP was 15.6% and 13.2% higher in MgOBF and SBF relative to BF. Hence, plant biomass, grain yield, and P uptake were highest in MgOBF and SBF, respectively at harvest. Optimized-biochar amendment stimulated microbial 16SrRNA gene diversity and suppressed the expression of P starvation response and P uptake and transport-related genes while stimulating P solubilization and mineralization genes. Thus, the optimized biochars promoted P availability via the combined processes of slow-release of retained phosphates, while inducing the microbial solubilization and mineralization of inorganic and organic P, respectively. Our study advances strategies for reducing cropland P limitation and reveals the potential of optimized biochars for improving P availability on the field scale.
| • | MgO and sepiolite doping optimized biochar’s surface properties for phosphorus (P) retention and slow release |
| • | The potential formation of Mg-PO4 phases on the optimized biochar surface regulated P retention and release |
| • | MgO and sepiolite-ptimized biochars increased soil available P by promoting microbial P mineralization and solubilization. |
To reveal the influence of the diversity of precursors on the formation of environmental persistent free radicals (EPFRs), pomelo peel (PP) and its physically divided portion, pomelo cuticle (PC), and white fiber (WF) were used as precursors to prepare six hydrochars: PPH-Fe, PCH-Fe, WFH-Fe, PPH, PCH, and WFH with and without Fe(III) addition during hydrothermal carbonization (HTC). PPH-Fe and WFH-Fe had higher EPFRs content (9.11 × 1018 and 8.25 × 1018 spins·g−1) compared to PPH and WFH (3.33 × 1018 and 2.96 × 1018 spins·g−1), indicating that iron-doping favored EPFRs formation. However, PCH-Fe had lower EPFRs content (2.78 × 1018 spins·g−1) than PCH (7.95 × 1018 spins·g−1), possibly due to excessive iron leading to the consumption of the generated EPFRs. For another reason, the required Fe(III) amount for EPFRs formation might vary among different precursors. PC has a lower concentration of phenolic compounds but 68–97% fatty acids, while WF and PP are rich in cellulose and lignin. In the Fenton-like reaction, oxygen-centered radicals of hydrochar played a significant role in activating H2O2 and efficiently degrading bisphenol A (BPA). Mechanisms of reactive oxygen species (ROS) generation in hydrochar/H2O2 system were proposed. EPFRs on hydrochar activate H2O2 via electron transfer, creating ·OH and 1O2, leading to BPA degradation. More importantly, the embedded EPFRs on the hydrochar's inner surface contributed to the prolonged Fenton-like reactivity of PPH-Fe stored for 45 days. This study demonstrates that by optimizing precursor selection and iron doping, hydrochars can be engineered to maximize their EPFRs content and reactivity, providing a cost-effective solution for the degradation of hazardous pollutants.
| • | Characteristics and mechanisms for the generation and consumption of EPFRs were proposed. |
| • | To favor g3-type EPFRs formation, the quantity of Fe(III) and aromatic compounds of the biomass should be matched. |
| • | The g3-type EPFRs on hydrochars played a major role in the Fenton-like reaction. |
| • | The external EPFRs of hydrochars were consumed easily while the internal EPFRs persisted during long-term storage. |
Hydrochar from waste biomass is a promising material for removing emerging contaminants (e.g., antibiotics) in water/soil environment. Abundant small-sized hydrochar particles (HPs) with a high content of reactive functional groups and high mobility are easily released into ecosystems through hydrochar applications. However, the photodegradation ability and corresponding structures of HPs are largely unknown, which hinder accurate estimation of the remediation effect of hydrochar in ecosystems. Herein, photodegradation performance of HP towards targeted norfloxacin (NOR, a typical antibiotic) under light irradiation (visible and UV light) were investigated after adsorption processes upon release into soil/water, and its reactive species and photoactive structures were clarified and compared with those of residual bulk hydrochar (BH) comprehensively. The results showed that: (1) photodegradation percentages of HPs were 4.02 and 4.48 times higher than those of BHs under UV and visible light, in which reactive species of both HPs and BHs were ·OH and ·O2 −; (2) density functional theory (DFT) results identified that the main photoactive structure of graphitic-N decreased the energy gap (Eg) of HPs, and C=O, COOH groups improved electron donating ability of BHs; (3) well-developed graphitization structure of HP resulted from higher polymerization reaction was an significant photoactive structure involving its superior photodegradation ability relative to that of BH. The distinct heterogeneities of photodegradation ability in HP and BH and underlying photoactive structures provide an in-depth understanding of hydrochar application for removing emerging contaminants in soil/water environment. Identifying photoactive structures is helpful to predict photodegradation ability of hydrochar according to their abundance.
| • | Photodegradation percentage of HP from hydrochar application was ~4 times superior to that of BH in degradation of NOR. |
| • | Major reactive species of HPs and BHs (·OH and ·O2 −) were generated from graphitic-N and C=O/COOH groups, respectively. |
| • | Photoactivity of HPs superior to BHs was mainly generated from well-developed graphitization structure of former. |
Crop residues and their derived biochar are frequently used for their potential to improve grain yield, soil fertility and carbon (C) sequestration. However, the effects of root are often overlooked, and the effects of chemical fertilizer (NPK) combined with root or its biochar on microbial community structure need further study. This study used 13C-labeled maize root, its biochar and soil with different fertilization for 8 years as materials and substrates. A 112-day incubation experiment was conducted to explore the effects of microbial community on the C processing. During incubation, the root-C (54.9%) mineralized significantly more than biochar-C (12.8%), while NPK addition significantly increased the root-C mineralization. Adding biochar alone did not significantly change the microbial community. Compared to the biochar treatment (BC), the root treatment (R) notably increased the contents of total phospholipid fatty acids (PLFAs), 13C-PLFA and the proportion of fungi and Gram-negative bacteria, but reduced the proportion of actinomycetes. The root mineralization was significantly correlated with the relative content of 13C-Gram-positive bacteria and 13C-fungi, while biochar mineralization was significantly correlated with the relative content of 13C-Gram-positive bacteria and 13C-actinomycetes. Notably, NPK addition significantly increased the contribution of biochar-C to PLFA-C pool, while decreasing the contribution of root-C. In summary, due to microbial adaptation to the lack of bioavailable C in biochar-amended soil, biochar can act as a buffer against the significant disturbance caused by NPK to microbial communities and native soil organic carbon (SOC), which contributes to the steady enhancement in soil C storage.
| • | The addition of biochar alone for 8 consecutive years did not change the composition of the microbial community structure, but the total PLFA content increased significantly compared to the control. |
| • | NPK addition reduced the proportion of microbial assimilation of root-C, while increasing the proportion of microbial assimilation of biochar-C. |
| • | The effect of NPK on microbial biomass is short-lived, but the effect on microbial community structure is long-lasting. |
| • | Biochar has a stronger buffering effect on the drastic changes in microbial communities and native SOC caused by NPK. |
Vermicomposting utilizes the synergistic effect of earthworms with microorganisms to accelerate the stabilization of organic matter in biowastes. Nevertheless, the exact mechanism behind the maturity of vermicompost and the growth of earthworms exposed to biochar of varying particle sizes remains unclear. This study presents an investigation of the effect of biochar particle size on earthworm (Eisenia fetida) survival, microbial diversity, and the quality of vermicompost products. To address these issues, pelletized dewatered sludge samples from a municipal sewage treatment plant were amended with pine-based biochar with particle sizes of 1–2 mm, 25–75 μm, 200 nm, and 60 nm as the substrate for vermicomposting. This study revealed that the addition of millimeter-scale biochar and micron-scale biochar significantly promoted the degradation of organic matter since the organic matter in the treatment with 1–2 mm biochar at the end of the vermicomposting experiment decreased by 12.6%, which was equivalent to a 1.9-fold increase compared with that of the control. Excessive nanopowdering of nanobiochar significantly affected the survival of earthworms and led to 24.4–33.3% cumulative mortality, while millimeter-scale (mm) biochar and micron-scale (μm) biochar achieved zero mortality. The findings of this study could be used for evaluating the potential impact of nanoscale biochar to earthworms and guiding biochar-augmented vermicomposting.
| 1. | The addition of 1–2 mm biochar resulted in a 1.9-fold greater reduction in organic matter compared to the control group. |
| 2. | The introduction of 25–75 μm biochar led to a significant 94% increase in earthworm cocoons. |
| 3. | The cumulative mortality rates of 200 nm and 60 nm biochar amendment reached peaks of 33.3% and 24.4% at first week, respectively. |
| 4. | Earthworms excrete mucus that effectively removes attached nanobiochar. |
Biochar (BC) applications in soil has positive effects on plant performance, particularly for loose soil in agricultural context. However, how biochar types affect plant performance of non-crop species and soil–plant carbon relationships is not clear. We selected five different BC types and three plant species to investigate the responses of plant performance and the soil–plant carbon relationship to BC effects. The result demonstrated that peanut shell BC led to the death of both R. tomentosa and C. edithiae, due to a reduction in nutrient uptake caused by higher soil electricity conductivity (2001.7 and 976.3 µS cm−1). However, the carbon content of S. arboricola increased by 57% in peanut shell BC-amended soil, suggesting that S. arboricola has a higher tolerance for soil salinity. Wood BC-amended soil led to better stomatal conductance (gs) and leaf area index (LAI) of both R. tomentosa and C. edithiae due to the higher water retention in the soil (22.68% and 20.79%). This illustrated that a higher amount of water retention brought by wood BC with a great amount of pore volume might be the limited factor for plant growth. The relationship between gs and LAI suggested that gs would not increase when LAI reached beyond 3. Moreover, wood and peanut shell BC caused a negative relationship between soil organic carbon and plant carbon content, suggesting that plants consume more carbon from the soil to store it in the plant. Overall, wood BC is recommended for plant growth of R. tomentosa and C. edithiae, and peanut shell BC is suggested for S. arboricola carbon storage.
| • | Peanut shell biochar enhanced soil salinity which causes the death of R. tomentosa and C. edithiae, while wood biochar is suitable for these plant species. |
| • | Wood and peanut shell biochar caused a negative relationship between soil organic carbon and plant carbon content. |
| • | The stomatal conductance will not increase when the leaf area reaches the limiting value 3. |
| • | An empirical function is developed to correlate plant carbon content and leaf area index under different biochar applications. |
Low-cost and green preparation of efficient sorbents is critical to the removal of organic contaminants during water treatment. In this study, the co-pyrolysis of macroalgae and oyster shell was designed to synthesize nitrogen-doped porous biochars for sorption removal of atrazine from water. Oyster shell played a significant role in opening pores in macroalgae-derived biochars, resulting in the surface area of the macroalgae (Enteromorpha prolifera and Ulva lactuca) and oyster shell co-pyrolyzed carbonaceous as high as 1501.80 m2 g−1 and 1067.18 m2 g−1, the pore volume reached 1.04 cm3 g−1 and 0.93 cm3 g−1, and O/C decreased to 0.09 and 0.08, respectively. The sorption capacity of atrazine to nitrogen-doped porous biochars (the Enteromorpha prolifera, Ulva lactuca and oyster shell co-pyrolyzed carbonaceous) reached 312.06 mg g−1 and 340.52 mg g−1. Pore-filling, hydrogen bonding, π-π or p-π stacking and electrostatic interaction dominated the multilayer sorption process. Moreover, the nitrogen-doped porous biochars showed great performance in cyclic reusability, and the Enteromorpha prolifera, Ulva lactuca and oyster shell co-pyrolyzed carbonaceous sorption capacity still reached 246.13 mg g−1 and 255.97 mg g−1, respectively. Thus, this study suggested that it is feasible and efficient to remove organic contaminants with the nitrogen-doped porous biochars co-pyrolyzed from macroalgae and oyster shell, providing a potential green resource utilization of aquatic wastes for environmental remediation.
| • | Nitrogen-doped porous biochars (NPBs) were derived from natural wastes. |
| • | Oyster shell enhanced the micropore and mesopore structures of NPBs. |
| • | Physical sorption dominated atrazine sorption onto the NPBs. |
Phosphorus-modified biochar has been proven to enhance the precipitation and complexation of heavy metal ions from wastewater. However, the current modification methods require large amounts of exogenous P and have high energy consumption. Hence, this study proposes and analyzes a strategy integrating biochar production, phosphorus wastewater treatment, dephosphorization waste recovery, and heavy metal removal. “BC-Ca-P” was derived from Ca-modified biochar after phosphorus wastewater treatment. The adsorption of Pb(II) by BC-Ca-P followed the Langmuir isotherm and pseudo–second–order kinetic models. The maximum adsorption capability of 361.20 mg·g−1 at pH 5.0 for 2 h was markedly greater than that of external phosphorous-modified biochar. The adsorption mechanisms were dominated by chemical precipitation and complexation. Furthermore, density functional theory calculations indicated that oxygen-containing functional groups (P-O and C-O) contributed the most to the efficient adsorption of Pb(II) onto BC-Ca-P. To explore its practical feasibility, the adsorption performance of BC-Ca-P recovered from an actual environment was evaluated. The continuous-flow adsorption behavior was investigated and well-fitted utilizing the Thomas and Yoon–Nelson models. There was a negligible P leakage risk of BC-Ca-P during heavy metal treatment. This study describes a novel and sustainable method to utilize dephosphorization waste for heavy metal removal.
| • | Dephosphorization biochar waste was used to sustainably remove heavy metals from wastewater. |
| • | Field-recovered dephosphorization biochar waste displayed high Pb adsorption capacity. |
| • | Dephosphorization biochar for heavy metal removal is an eco–friendly waste–reduction and resource–utilization method. |
Biochar, produced from the thermochemical conversion of biomass waste, has various applications owing to its broad utility and advantageous properties. This study employs a scientometric approach to comprehensively assess the advancements in biochar application from 2022 to 2023. Utilizing 13,357 bibliographic records sourced from the Web of Science Core Collection with the search term “biochar”, the analysis focuses on authorship, national contributions, and keyword trends. Findings demonstrate a continual rise in annual publications since 2009, albeit with a moderated growth rate in 2023. China leads in publication outputs, followed by USA and India, with Hailong Wang emerging as a prominent figure in biochar research. Keyword co-occurrence analyses identify key research themes such as biochar’s role in climate change mitigation, easing salinity and drought stress, immobilizing toxic metals, degrading organic pollutants, serving as additives in anaerobic digestion, and functioning as electrodes in microbial fuel cells. Among these, biochar’s application for global climate change mitigation gains significant attention, while its utilization as electrodes in microbial fuel cells emerges as a promising research frontier, indicating the growing need for sustainable energy sources. The study also outlines critical research gaps and future priorities for enhancing biochar application. Overall, it highlights the diverse applicability of biochar and offers valuable insight into research progression and forthcoming directions in biochar studies.
| • | Utilization of bibliometric review for keyword analysis. |
| • | Examination of recent developments in biochar application. |
| • | The emerging focus on biochar’s effectiveness as electrodes in microbial fuel cells (MFCs). |
| • | Suggested future research directions and priorities for sustainable biochar application. |
Boron-doped biochar (B-BC) was synthesized by pyrolysis using solid waste of sorghum straw as raw material. The specific surface area of B-BC increased significantly by 2.38 times compared to that of pure BC. This enhancement allowed B-BC (0.3 g L−1) to achieve complete adsorption of 10 mg L−1 tartrazine (TTZ) within 40 min. Moreover, acidic conditions were more favorable for TTZ adsorption, achieving complete removal of TTZ in only 15 min at a pH of 3.0. Interestingly, the adsorption rate of TTZ by B-BC in the presence of 0.05 M Cl− was approximately 2.12 times higher than that in the absence of Cl−. When other background electrolytes were present, excluding PO4 3−, complete adsorption of TTZ could also be achieved within 60 min. Thermodynamic analysis and DFT calculations described the parameters of B-BC for TTZ adsorption, including (< 0 kJ mol−1), (− 2.199 kJ mol−1), (− 6.068 J mol−1 K−1), and the adsorption energy (E ads = − 0.6919 eV), indicating a tendency towards a spontaneous adsorption process. Moreover, the strong electron transfer ability of B-BC and the oxygen-containing groups promoted the activation of PDS and generation of active substances such as 1O2, O2 •−, and SO4 •−, thereby degrading TTZ into products with lower biological toxicity. When the added PDS was only 0.1 mM, the degradation rate constant of TTZ could reach 0.1481 min−1. Furthermore, boron doping enhanced the stability of biochar, enabling the complete removal of 10 mg L−1 TTZ even after recycling and regeneration. In summary, this study offers a practical solution for the resource utilization of solid waste sorghum straw and the treatment of TTZ-polluted wastewater.
| • | Boron doping significantly increased the specific surface area of biochar by 2.38 times. |
| • | B-BC exhibited complete adsorption of TTZ in only 15 min at a pH of 3.0. |
| • | Addition of 0.05 M Cl− increased the adsorption rate of TTZ on B-BC by 1.12 times. |
| • | Free radicals and nonradicals contributed to TTZ degradation in B-BC/PDS system. |
| • | Degradation products of TTZ displayed reduced toxicity to typical aquatic organisms. |