Biochar has the potential to provide a multitude of benefits when used in soil remediation and increasing soil organic matter enrichment. Nevertheless, the intricated, hydrophobic pores and groups weaken its water-holding capacity in dry, sandy soils in arid lands. In order to combat this issue, starch-carbon-based material (SB), sodium alginate-carbon-based material (SAB), and chitosan-carbon-based material (CB) have been successfully synthesized through the graft-polymerization of biochar (BC). A series of soil column simulations were used to scrutinize the microstructure of the carbon-based material and explore its water absorption properties and its effects on sandy soil water infiltration, water retention, and aggregation. The results indicated that SB, SAB, and CB achieved water maximum absorption rates of 155, 188, and 172 g g⁻¹, respectively. Considering their impact on sandy soils, SB, SAB, and CB lengthened infiltration times by 1920, 3330, and 3880 min, respectively, whilst enhancing the water retention capabilities of the soil by 18%, 25%, and 23% in comparison to solely adding BC. The utilization of these innovative materials notably encouraged the formation of sandy soil aggregates ranging from 2.0 to 0.25 mm, endowing the aggregates with enhanced structural stability. Findings from potting experiments suggested that all three carbon-based materials were conducive to the growth of soybean seeds. Thus, it is evident that the carbon-based materials have been fabricated with success, and they have great potential not only to significantly augment the water retention capacities and structural robustness of sandy soils in arid areas, but also to bolster the development of soil aggregates and crop growth. These materials possess significant application potential for enhancing the quality of sandy soils in arid and semi-arid regions.

Due to anthropogenic activities, heavy metal (HM) pollution in soils has increased, resulting in severe ecological problems and posing a constant threat to human health. Among various remediation methods, bacterial remediation is a relatively clean, efficient, and minimally negative approach. However, bacterial agents face multiple environmental stresses, making them challenging to achieve long-lasting and stable restoration effects. To address this issue, supportive organic substances such as biochar can be added to the soil with bacteria. According to bibliometric studies, integrating biochar and bacteria is extensively researched and widely used for HM-contaminated soil remediation. By integrating biochar and bacteria, heavy metals in the soil can be remediated, and soil conditions can be improved over time. Bacteria can also better promote plant growth or contribute effectively to phytoremediation processes when assisted by biochar. However, the remediation agents integrating biochar and bacteria are still some distance away from large-scale use because of their high cost and possible environmental problems. Therefore, further discussion on the interaction between biochar and bacteria and the integration approach, along with their remediation efficiency and environmental friendliness, is needed to achieve sustainable remediation of HM-contaminated soils by integrating biochar and bacteria. This paper discusses the potential mechanisms of biochar-bacteria-metal interactions, current advancements in biochar-bacteria combinations for HM-contaminated soil treatment, and their application in sustainable remediation, analyzes the interaction between biochar and bacteria and compares the remediation effect of different ways and feedstocks to integrate biochar and bacteria. Finally, future directions of biochar-bacteria combinations are presented, along with evidence and strategies for improving their commercialization and implementation.

Biochar is a potential porous carbon to remove the contaminants from aquatic environments. Herein, N-doped hierarchical biochar was produced by the combined approach of ammonia torrefaction pretreatment (ATP) and alkali activation. ATP could not only incorporate N element into poplar wood, but obtain the loose structure of poplar wood. The highest surface area of N-doped hierarchical biochar was 2324.61 m² g⁻¹ after ammonia wet torrefaction pretreatment, which was higher than that of activation carbon (1401.82 m² g⁻¹) without torrefaction pretreatment, the hierarchical biochar (2111.03 m² g⁻¹) without ammonia atmosphere. The N-doped hierarchical biochar presented the highest adsorption capacity (564.7 mg g⁻¹) of methyl orange (MO), which was 14.64-fold of that on biochar without N doping. In addition, the pseudo-second-order and Langmuir model fitted well with the adsorption kinetics and isotherms of the N-doped hierarchical biochar. The incorporation of nitrogen element could not only tune the distribution of surface electrons on biochar, but optimize the ambient condition of adsorption active sites as well. The adsorption of MO might occur on the N-/O-containing functional groups through the electrostatic interaction, the π-π dispersion interaction, and the hydrogen bonding. The density functional theory showed that the graphitic-N and pyridinic-N were the dominant adsorption active sites.

Fertilizer-intensive agriculture is a leading source of reactive nitrogen (Nr) emissions that damage climate, air quality, and human health. Biochar has long been studied as a soil amendment, but its influence on Nr emissions remains insufficiently characterized. More recently, the pyrolysis of light hydrocarbons has been suggested as a source of hydrogen fuel, resulting in a solid zero-valent carbon (ZVC) byproduct whose impact on soil emissions has yet to be tested. We incorporate carbon amendment algorithms into an agroecosystem model to simulate emission changes in the year following the application of biochar or ZVC to the US. fertilized soils. Our simulations predicted that the impacts of biochar amendments on Nr emissions would vary widely (− 17% to + 27% under 5 ton ha⁻¹ applications, − 38% to + 18% under 20 ton ha⁻¹ applications) and depend mostly on how nitrification is affected. Low-dose biochar application (5 ton ha⁻¹) stimulated emissions of all three nitrogen species in 75% of simulated agricultural areas, while high-dose applications (20 ton ha⁻¹) mitigated emissions in 76% of simulated areas. Applying zero-valent carbon at 20 ton ha⁻¹ exhibited similar effects on nitrogen emissions as biochar applications at 5 ton ha⁻¹. Biochar amendments are most likely to mitigate emissions if applied at high rates in acidic soils (pH < 5.84) with low organic carbon (< 55.9 kg C ha⁻¹) and inorganic nitrogen (< 101.5 kg N ha⁻¹) content. Our simulations could inform where the application of carbon amendments would most likely mitigate Nr emissions and their associated adverse impacts.

The intensification of estrogen non-point source pollution has drawn global attention due to their contribution to ecological environment problems worldwide, and it is critical to develop effective, economic and eco-friendly methods for reducing estrogens pollution. To address the agglomeration and oxidation of nano zero-valent iron (nZVI), biochar-nanoscale zero-valent iron composite (nZVI-biochar) could be a feasible choice for estrogens removal. This study summarized biochar and nZVI-biochar preparation, characterization, and unusual applications for estrone (E1), 17β-estradiol (E2), and estriol (E3) removal. The properties of biochar and nZVI-biochar in characterization, effects of influencing factors on the removal efficiency, adsorption kinetics, isotherm and thermodynamics were investigated. The experiment results showed that nZVI-biochar exhibited the superior removal performance for estrogens pollutants compared to biochar. Based on the quasi-second-order model, estrogens adsorption kinetics were observed, which supported the mechanism that chemical and physical adsorption existed simultaneously on estrogens removal. The adsorption isotherm of estrogens could be well presented by the Freundlich model and thermodynamics studies explained that nZVI-biochar could spontaneously remove estrogens pollutants and the main mechanisms involved π-π interaction, hydrophobic interaction, hydrogen bonding and degradation through ring rupture. The products analyzed by GC–MS showed that estrogens degradation was primarily attributed to the benzene ring broken, and Fe³⁺ promoted the production of free radicals, which further proved that nZVI-biochar had the excellent adsorption performances. Generally, nZVI-biochar could be employed as a potential material for removing estrogens from wastewater.

The use of inorganic nitrogen (N) fertilizers has increased drastically to meet the food requirements of the world's growing population. However, the excessive use of chemical nitrogen fertilizer has caused a series of soil and environmental problems, such as soil hardening, lower nitrogen use efficiency (NUE), nitrate pollution of water sources, nitrous oxide emissions, etc. In this review, we aimed to elaborate and discuss the role of engineered biochar in inducing the stability of water-stable macroaggregates, improving inorganic N transformation, and utilization efficiency to address the current uncertainties of nitrogen loss and maintaining soil and water quality. Firstly, we elucidated the characteristics of engineered biochar in improving biochar quality to work as a multifunctional player in the ecosystem and promote resource utilization, soil conservation, and ecosystem preservation. Secondly, we discussed how the engineered biochar modulates the stability of water-stable macroaggregates and soil inorganic nitrogen transformation to enhance plant response under various toxic or deficient nitrogen conditions in the soil. Thirdly, the role of engineered biochar in biological nitrogen fixation, mediating nirK, nirS, and nosZ genes to promote the conversion of N₂O to N₂, and decreasing denitrification and N₂O emission was reviewed. Altogether, we suggest that engineered biochar amendment to soil can regulate soil water-stable macroaggregates, reduce N input, improve nitrogen metabolism, and finally, NUE and crop growth. To the best of our knowledge, this is the first time to evaluate the combined interactions of "engineered biochar × soil × NUE × crop growth,” providing advantages over the increasing N and water utilization and crop productivity separately with the aim of enhancing the stability of water-stable macroaggregates and NUE together on a sustainable basis.

Soil harbors a huge diversity of microorganisms and serves as the ecological and social foundation of human civilization. Hence, soil health management is of utmost and consistent importance, aligning with the United Nations Sustainable Development Goals. One of the most hazardous contaminants in soil matrix is potentially toxic elements (PTEs), which can cause stress in soil indigenous microorganisms and severely jeopardize soil health. Biochar technology has emerged as a promising means to alleviate PTE toxicity and benefit soil health management. Current literature has broadly integrated knowledge about the potential consequences of biochar-amended soil but has focused more on the physical and chemical responses of the soil system than microbiological attributes. In consideration of the indispensable roles of soil microbials, this paper first introduces PTE-induced stresses on soil microbials and then proposes the mechanisms of biochar’s effects on soil microbials. Finally, microbial responses including variations in abundance, interspecific relationships, community composition and biological functions in biochar-amended soil are critically reviewed. This review thus aims to provide a comprehensive scientific view on the effect of biochar on soil microbiological health and its management.

Increased biogas residue related to the rapid development of anaerobic fermentation has become an urgent environmental problem. The pyrolysis of biogas residue into biochar is one of the most promising treatments. In this study, biochar derived from biogas residue was prepared, and the degradation efficiency of phenol by permanganate (KMnO₄) increased from 25.3% to 73.4% in 60 min in the presence of biogas residue biochar (BRB). KMnO₄ reacted with BRB to produce intermediate manganese dioxide (MnO₂), while BRB was activated. The specific surface area increased by 132.25%, and the oxygen-containing functional groups C=O, C−O, and COOH increased after the reaction. The generated MnO₂ complexed with BRB to form MnO₂@BRB. The newly formed MnO₂@BRB catalyzed KMnO₄ to remove phenol, which explains the high removal efficiency of phenol. A significant removal rate was also observed for antibiotics and chlorophenols, which suggested that the KMnO₄/BRB system has a relatively high ability to oxidize organic pollutants. In addition, the co-existing metal ions and the natural environment had little influence on the removal efficiency of the KMnO₄/BRB system. This work provides a novel technology for the resource utilization of biogas residue and improved organic pollutant removal efficiency of KMnO₄ in the presence of BRB.

The Climate Change Conference of Parties (COP) 21 in December 2015 established Nationally Determined Contributions toward reduction of greenhouse gas emissions. In the years since COP21, it has become increasingly evident that carbon dioxide removal (CDR) technologies must be deployed immediately to stabilize concentration of atmospheric greenhouse gases and avoid major climate change impacts. Biochar is a carbon-rich material formed by high-temperature conversion of biomass under reduced oxygen conditions, and its production is one of few established CDR methods that can be deployed at a scale large enough to counteract effects of climate change within the next decade. Here we provide a generalized framework for quantifying the potential contribution biochar can make toward achieving national carbon emissions reduction goals, assuming use of only sustainably supplied biomass, i.e., residues from existing agricultural, livestock, forestry and wastewater treatment operations. Our results illustrate the significant role biochar can play in world-wide CDR strategies, with carbon dioxide removal potential of 6.23 ± 0.24% of total GHG emissions in the 155 countries covered based on 2020 data over a 100-year timeframe, and more than 10% of national emissions in 28 countries. Concentrated regions of high biochar carbon dioxide removal potential relative to national emissions were identified in South America, northwestern Africa and eastern Europe.

Biochar has been shown to improve soil properties and plant productivity in soils with inherently low fertility. However, little has been reported for upland corns under dry and wet precipitation regimes. This study investigates the effect of biochar addition on a range of soil physicochemical, biological, and hydrological properties, and corn growth and productivity under agrometeorological drought and wet conditions. Here, experiments were laid out in a randomized complete block design with three replications at two sites during 2017 and 2018 in South Korea. Treatments included (i) CN: control (ii) IF: inorganic fertilizer (N–P–K) at 145–30–60 kg ha⁻¹; (iii) BS: barley straw at 5 t ha⁻¹; (iv) CWBC: corn waste biochar at 5 t ha⁻¹; (v) CWBC + IF: corn waste biochar + inorganic fertilizer; (vi) CWBC + BS: corn waste biochar + barley straw. The year 2017 was relatively dry, whereas the year 2018 was wet. Despite drought conditions in the year 2017, biochar facilitated soil water conservation. However, higher precipitation in 2018 increased  the quantity and distribution of soil water and nutrients in the top 15 cm. Biochar reduced soil bulk density, and increased porosity, cation exchange capacity and total organic carbon in both years but increased total bacterial counts during the dry year only. Bacterial population was generally higher under wet conditions. Similarly, more soil CO₂ was emitted in the wet year than in the dry year. Results further indicated that biochar can enhance corn biomass and grain yield regardless of precipitation conditions. The grain index was, however, affected by rainfall and was significantly different across treatments in the year 2018 only. All biomass, grain yield, and grain index were highest in CWBC + IF treatment and lowest under CN treatment. Indeed, biochar addition appeared to improve soil quality and soil conditioning effects in the drought and wet years, ameliorating soil and plant properties. Overall, biochar can improve water and nutrients storage, availability, and uptake, and therefore corn productivity during hydrological extremes.

Root and tuber crops are important sources of food and provide income for millions of people worldwide besides an observed high demand for organically produced harvests. Hence, recent attention has been given to utilizing biochar, a carbon-rich material produced from the pyrolysis of organic materials, which improves soil structure, water-holding capacity, and nutrient availability, as an amendment to produce organic root and tuber crops. These effects are caused by the formation of organic coatings on the surface of biochar, which decreases hydrophobicity and increases the ability to retain nutrients, acting as a slow-release mechanism delivering nutrients dependent on plant physiological requirements. However, comprehensive studies on the impact of biochar application on root and tuber crop growth, productivity, and effectiveness in eliminating soil parasites have not been extensively studied. Thus, the purpose of this review is to explore the use of biochar and biochar-based soil amendments and their potential applications for improving the growth, yield, and efficacy of controlling parasitic nematodes in a wide range of root crops. Most of the studies have investigated the effects of biochar on cassava, sweet potatoes, and minor root crops such as ginger and turmeric. It has been observed that biochar application rates (5–20 t ha⁻¹) increase the vine length and the number of leaves, tubers, and tuber weight. The addition of biochar demonstrates the ability to control plant-parasitic nematodes in a rate-dependent manner. While biochar has shown promising results in improving crop growth and yield of limited root and tuber crops based on a few biochar types, ample opportunities are around to evaluate the influence of biochar produced in different temperatures, feedstock, modifications and controlling parasitic nematodes.

Biochar has been considered an effective approach as soil amendment for decreasing incidences of disease and regulating microbial populations in continuous-cropping soil. Although researches have extensively focused on changes of soil microbes and unbalance of nutrition in continuous-cropping soil, the relationship between soil properties and pathogens by biochar application remains poorly understood. In this study, we applied ITS ribosomal RNA gene profiling to analyze tobacco root microbiota of biochar and non-biochar treatment in a 3-year continuous-cropping tobacco field, comparing firstly planting tobacco as control. We found that biochar application decreased the relative abundance of the soil fungal pathogens (Ceratobasidium and Monosporascus), which are the prime pathogens of tobacco root rot in continuous-cropping soil. Using RDA, co-occurrence and PLS-PM approaches, we provided evidence that there was a negative correlation between fungal genera (especially for Ceratobasidium and Monosporascus) and soil polyphenol oxidase (PPO) activity (R²_{incidence rate} = − 0.930, R²_{disease index} = − 0.905, both p < 0.001). The PPO was up-regulated by different biochar treatment intensities. Together, we demonstrated that biochar in continuous-cropping soil regulated the soil PPO activity to suppress pathogens, and further decrease incidence of root rot. Notably, biochar application forward continuous cropping was more effective for the continuous-cropping soil improvement than the other treatments. The data should help in appropriate timing of biochar application for alleviating continuous-cropping obstacle.

Goethite nanoparticles modified biochar (FBC) could address the weak effectiveness of conventional biochar commonly to process heavy metal(loids)  (HMs) co-contamination with different charges. However, few studies have focused on the change of soil mechanical properties after stabilization. In this study, FBC was synthesized to stabilize simultaneously arsenic (As (V)) (anions) and cadmium (Cd (II)) (cations) in co-contaminated soils. Batch adsorption, leaching toxicity, geotechnical properties and micro-spectroscopic tests were comprehensively adopted to investigate the stabilization mechanism. The results showed that FBC could immobilize As (V) mainly through redox and surface precipitation while stabilizing Cd (II) by electrostatic attraction and complexation, causing soil agglomeration and ultimately making rougher surface and stronger sliding friction of contaminated soils. The maximum adsorption capacity of FBC for As (V) and Cd (II) was 31.96 mg g⁻¹ and 129.31 mg g⁻¹, respectively. Besides, the dosages of FBC required in contaminated soils generally were approximately 57% higher than those in contaminated water. FBC promoted the formation of small macroaggregates (0.25–2 mm) and the shear strengths of co-contaminated soils by 21.40% and 8.34%, respectively. Furthermore, the soil reutilization level was significantly improved from 0.14–0.46 to 0.76–0.83 after FBC stabilization according to TOPSIS method (i.e., technique for order preference by similarity to an ideal solution). These findings confirm the potential of FBC in immobilizing As (V) and Cd (II) of co-contaminated soils and provide a useful reference for green stabilization and remediation of HMs co-contaminated sites.

Highly efficient isomerization of glucose to fructose is essential for valorizing cellulose fraction of biomass to value-added chemicals. This work  provided an innovative method for preparing Mg-biochar and Mg–K-biochar catalysts by impregnating either MgCl₂ alone or in combination with different K compounds (Ding et al. in Bioresour Technol 341:125835, 2021, https://doi.org/10.1016/j.biortech.2021.125835 and KHCO₃) on cellulose-derived biochar, followed by hydrothermal carbonization and pyrolysis. Single active substance MgO existing in the ₁₀Mg–C could give better catalytic effect on glucose isomerization than the synergy of MgO and KCl crystalline material present in ₁₀Mg–KCl–C. But the catalytic effect of ₁₀Mg–C was decreased when the basic site of MgO was overloaded. Compared to other carbon-based metal catalysts, ₁₀Mg–KHCO₃–C with 10 wt% MgCl₂ loading had  excellent catalytic performance, which gave  a higher fructose yield (36.7%) and selectivity (74.54%), and catalyzed excellent glucose conversion (53.99%) at 100 °C in 30 min. Scanning electron microscope–energy dispersive spectrometer and X-Ray diffraction revealed that the distribution of Mg²⁺ and K⁺ in ₁₀Mg–KHCO₃–C  was uniform and the catalytic active substances (MgO, KCl and K₂CO₃) were more than ₁₀Mg–C (only MgO). The synergy effects of MgO and K₂CO₃ active sites enhanced  the pH of reaction system and  induced H₂O ionization to form considerable OH⁻ ions, thus easily realizing a deprotonation of glucose and effectively catalyzing the isomerization of glucose. In this study, we developed a highly efficient Mg–K-biochar bimetallic catalyst for glucose isomerization and provided  an efficient method for cellulose valorization.

Various human activities have led to multiple contamination of natural water systems. The present study investigated the effect of a novel multifunctional biochar to treat nutrients, oil, and harmful algae in water. Specifically, magnesium (Mg) and biosurfactant rhamnolipid (RL) were incorporated into biochar, including Mg-biochar, RL-biochar, and Mg-RL-biochar. Their adsorption efficiency on phosphate and total petroleum hydrocarbons (TPH) was evaluated in separate batch studies. Also, the inhibition effect of RL-modified biochars on cyanobacteria was investigated. The results showed that Mg-impregnated biochar showed high adsorption capacity on phosphate (118 mg g⁻¹), while RL-modified biochar significantly reduced TPH (especially aromatic and light aliphatic fraction) with adsorption capacity of 44.4 mg g⁻¹. The inhibition effects of biochar composites on algae in water without contaminants were in order of Mg-RL-biochar > RL-biochar > biochar with biomass reduction ranging 61–64%. Overall, Mg-RL-biochar was  suggested based on this study due to its ability to remove PO₄³⁻ and TPH, and inhibit the growth of toxic algae.

Biochar with a highly accessible specific surface area can display a higher performance when it is used as the cathode of lithium-ion capacitors. Facing the complex composition and diversity of biomass precursors, there is a lack of a universally applicable method to construct hierarchical porous biochar controllably. In this work, a multi-stage activation strategy combining the feature of different activation methods is proposed for this target. To confirm the porous characteristic in prepared samples, N₂ adsorption–desorption and transmission electron microscope were used. As the optimal sample, BC-P3K4S had the highest specific surface area of 3583.3 m² g⁻¹. Evaluated as the electrode for a lithium-ion capacitor, BC-P3K4S displayed a capacity of 139.1 mAh g⁻¹ at 0.1 A g⁻¹. After coupling it with pre-lithiated hard carbon, the full device exhibited a high energy density of 129.3 W h kg⁻¹ at 153 W kg⁻¹. The work outlined herein offers some insights into the preparation of hierarchical porous biochar from complex biomass by multistep activation method.

Salt-affected soils urgently need to be remediated to achieve the goals of carbon neutrality and food security. Limited reviews are available on biochar performance in remediating salt-affected soils in the context of carbon neutrality and climate change mitigation. This work summarized the two pathways to achieve carbon neutrality during remediating salt-affected soils using biochars, i.e., biochar production from sustainable feedstock using thermal technologies, application for promoting plant productivity and mitigating greenhouse gas (GHG) emission. Converting biomass wastes into biochars can reduce GHG emission and promote carbon dioxide removal (CDR), and collection of halophyte biomass as biochar feedstocks, development of biochar poly-generation production systems with carbon neutrality or negativity could be promising strategies. Biochar can effectively improve plant growth in salt-affected soils, showing that the grand mean of plant productivity response was 29.3%, via improving physicochemical characteristics, shifting microbial communities, and enhancing plant halotolerance. Moreover, biochar can mitigate GHG emission via inducing negative priming effect, improving soil properties, changing microbial communities associated with carbon and nitrogen cycle, direct adsorption of GHG. However, biochar also may pose negative effects on plant growth because of stress of toxic compounds and free radicals, and deterioration of soil properties. The promoted GHG emission is mainly ascribed to positive priming effect, and provision of labile carbon and inorganic nitrogen fractions as microbial substrates. Finally, this review pointed out the gaps in the current studies and the future perspectives. Particularly, the development of “carbon neutral” or “carbon negative” biochar production system, balancing the relationship of biochar effectiveness and functionality with its environmental risks and costs, and designing biochar-based GHG adsorbents would be important directions for remediating salt-affected soils to achieve carbon neutrality and abate climate change.

Biochar can change the availability and morphology of soil Cd. However, the influence of biochar on Cd chemical form and subcellular fraction in rice is poorly understood, particularly under different irrigation methods. A pot experiment of biochar application combined with two irrigation methods (continuous flooding and intermittent irrigation, CF and II) was conducted. The Cd accumulation, chemical form and subcellular fraction in rice organs and the associated physiological responses were examined. Biochar significantly reduced soil available Cd (30.85–47.26% and 32.35–52.35%) under CF and II but increased the Cd content (30.4–63.88% and 13.03–18.59%) in brown rice. Additionally, the Cd content in shoots/grains under II was higher than that under CF. Biochar elevated the Cd soluble fraction in roots while lowered the cell wall fraction under both irrigation methods, whereas the opposite result was observed in leaves. Biochar increased water-, ethanol-, and NaCl-extractable Cd in roots meanwhile increased ethanol-extractable Cd in leaves under both irrigation methods. Moreover, the total amount of water-, ethanol-, and NaCl-extractable Cd in rice roots was higher under II than under CF. Related hormones and antioxidant enzymes may also be involved in biochar-mediated Cd accumulation in rice grains. Thus, changes in Cd chemical form and subcellular fraction in the root and leaf are the main mechanisms of biochar-induced rice grains Cd accumulation.

Rapid development in industrialization and urbanization causes serious environmental issues, of which acid rain is one of the quintessential hazards, negatively affecting soil ecology. Liming has been investigated for a long time as the most effective amendment to alter the adverse effects of soil acidity resulting from acid rain. Herein, this study tested the biochar produced from invasive plants as an alternative amendment and hypothesized that biochar can maintain better availability of macronutrients under acid rain than liming by improving soil chemical and biological properties. Therefore, a pot experiment was conducted to compare the effects of lime and biochar at two rates (1% and 3%) on soil available nitrogen (N), phosphorous (P) and potassium (K) under simulated acid rain of two pH levels (4.5: pH_4.5 and 2.5: pH_2.5) as compared with tap water (pH_7.1) as a control treatment. Biochar was produced using different invasive plants, including Blackjack (Biden Pilosa), Wedelia (Wedelia trilobata) and Bitter Vine (Mikania micrantha Kunth). Liming decreased the availability of soil N, P, and K by 36.3% as compared with the control due to the great increment in soil pH and exchangeable calcium (Ca²⁺) by 59% and 16-fold, respectively. Moreover, liming reduced the alpha diversity of soil bacteria and fungi by 27% and 11%, respectively. In contrast, biochar at different types and rates resulted in a fourfold increment in the available N, P, and K as an average under acid rain (pH_4.5 and pH_2.5) owing to maintaining a neutral pH (6.5–7), which is the most favorable level for soil microbial and enzymatic activites, and the bioavailability of soil nutrients. Furthermore, biochar caused balanced increments in Ca²⁺ by threefold, cation exchange capacity by 45%, urease activity by 16%, and fungal diversity by 10%, while having a slight reduction in bacterial diversity by 2.5%. Based on the path, correlation, and principal component analyses, the exchangeable aluminum was a moderator for the reductions in macronutrients’ availability under acid rain, which decreased by 40% and 35% under liming and biochar, respectively. This study strongly recommended the use of biochar from invasive plants instead of lime for sustainable improvements in soil properties under acid rain.

In the last few decades, sulfonated carbon materials have garnered significant attention as Brønsted solid acid catalysts. The sulfonation process and catalytic activity of sulfonated biochar can be influenced by the aromaticity and degree of condensation exhibited by biochar. However, the relationships between the aromaticity, sulfonating ability, and resultant catalytic activity are not fully understood. In this study, biochar samples pyrolyzed at 300–650 °C exhibiting different aromaticity and degrees of condensation were sulfonated and employed as sulfonate-bearing solid catalysts for hydrolytically removing tylosin. They exhibited excellent hydrolytic performance and their kinetic constants were positively correlated with the total acidity and negatively correlated with their aromaticity. This study has uncovered the relationship between the structure, properties, sulfonating ability, and subsequent hydrolytic performance of biochar samples. It was observed that the aromaticity of biochar decreased as the pyrolysis temperature increased. Lower pyrolysis temperatures resulted in a reduced degree of condensation, smaller ring size, and an increased number of ring edge sites available for sulfonation, ultimately leading to enhanced catalytic performance. These findings provide valuable insights into the fundamental chemistry behind sulfonation upgrading of biochar, with the aim of developing functional catalysts for mitigating antibiotics in contaminated water.

Plants regulate root exudates to form the composition of rhizosphere microbial community and resist disease stress. Many studies advocate intervention with biochar (BC) and exogenous microbe to enhance this process and improve plant defenses. However, the mechanism by which BC mediates exogenous microorganisms to enhance root exudate-soil microbial defensive feedback remains unclear. Here, a BC-based Bacillus subtilis SL-44 inoculant (BC@SL) was prepared to investigate the defensive feedback mechanism for plants, which  enhanced plant growth and defense more than BC or SL-44 alone. BC@SL not only strengthened the direct inhibition of Rhizoctonia solani Rs by solving the problem of reduced viability of a single SL-44 inoculant but also indirectly alleviated the Rs stress by strengthening plant defensive feedback, which  was specifically manifested by the following: (1) increasing the root resistance enzyme activities (superoxide dismutase up to 3.5 FC); (2) increasing the abundance of beneficial microbe in soil (0.38–16.31% Bacillus); and (3) remodeling the composition of root exudates (palmitic acid 3.95–6.96%, stearic acid 3.56–5.93%, 2,4 tert-butylphenol 1.23–2.62%, increasing citric acid 0.94–1.81%, and benzoic acid 0.97–2.13%). The mechanism reveals that BC@SL can enhance the positive regulatory effect between root exudates and microorganisms by optimizing their composition. Overall, BC@SL is a stable and efficient new solid exogenous soil auxiliary, and this study lays the foundation for the generalization and application of green pesticides.

The biochar amendment plays a vital role in maintaining soil health largely due to its effects on soil microbial communities. However, individual cases and the variability in biochar properties are not sufficient to draw universal conclusions. The present study aimed to reveal how the biochar application affects soil microbial communities. Metadata of 525 ITS and 1288 16S rRNA sequencing samples from previous studies were reanalyzed and machine learning models were applied to explore the dynamics of soil microbial communities under biochar amendment. The results showed that biochar considerably changed the soil bacterial and fungal community composition and enhanced the relative abundances of Acidobacteriota, Firmicutes, Basidiomycota, and Mortierellomycota. Biochar enhanced the robustness of the soil microbial community but decreased the interactions between fungi and bacteria. The random forest model combined with tenfold cross-validation were used to predict biomarkers of biochar response, indicating that potentially beneficial microbes, such as Gemmatimonadetes, Microtrichales, Candidatus_Kaiserbacteria, and Pyrinomonadales, were enriched in the soil with biochar amendment, which promoted plant growth and soil nutrient cycling. In addition, the biochar amendment enhanced the ability of bacteria to biosynthesize and led to an increase in fungal nutrient patterns, resulting in an increase in the abundance and diversity of saprophytic fungi that enhance soil nutrient cycling. The machine learning model more accurately revealed how biochar affected soil microbial community than previous independent studies. Our study provides a basis for guiding the reasonable use of biochar in agricultural soil and minimizing its negative effects on soil microecosystem.

Sludge biochar, a carbonized product of raw sludge, contains porous architectures that can act as epicenters for adsorbing external molecules through physical or chemical bonding. Sludge biochar also immobilizes innate micropollutants, which is advantageous over conventional sludge disposal methods. To date, numerous strategies have been discovered to improve sludge biochar morphology, but the influential factors, pore tuning mechanisms, and process feasibility remain imprecise. This knowledge gap limits our ability to design a robust sludge-based biochar. Herein, we present state-of-the-art sludge biochar synthesis methods with insight into structural and chemical transformation mechanisms. Roadblocks and novel concepts for improving sludge biochar porous architecture are highlighted. For the first time, sludge biochar properties, adsorption performances, and techno-economic perspectives were compared with commercial activated carbon (AC) to reveal the precise challenges in sludge biochar application. More importantly, sludge biochar role in carbon sequestration is detailed to demonstrate the environmental significance of this technology. Eventually, the review concludes with an overview of prospects and an outlook for developing sludge biochar-based research.

The widespread organic pollutants in wastewater are one of the global environmental problems. Advanced oxidation processes (AOPs) are widely used because of their characteristics of high efficiency and strong oxidation. However, AOPs may have some defects, such as incomplete mineralization of organic pollutants and the generation of toxic by-products during the degradation process, thus it is essential to seek efficient and green wastewater treatment technologies. Coupling different AOPs or other processes is beneficial for the mineralization of pollutants and reduces ecological risks to the environment. It is worth noting that carbonaceous materials (CMs) have received widespread attention and application in the degradation of organic pollutants in water by advanced oxidation coupling processes (C-AOPs) due to their excellent physicochemical properties in recent years. However, the behaviors and mechanisms of C-AOPs based on CMs on the degradation of organic pollutants are still unknown. Therefore, it is essential to comprehensively summarize the recent research progress. In this review, the applications of different CMs in C-AOPs were reviewed first. Secondly, the synergistic mechanisms of the C-AOPs based on different CMs were discussed. Then, toxic intermediates were explored and important toxicity assessment methods were proposed. Finally, the application potential of the C-AOPs in the future and the challenges were proposed. This review provides an important reference for the application and optimization of the C-AOPs in organic wastewater treatment in the future.

Bio-tar extra-produced from biomass pyrolysis is prone to pose a threat to environment and human health. A novel N-doped porous electrode from bio-tar was produced under dual-activation of urea and KOH in this study. One-pot dual-activation played significant roles in N-functional group and micro-mesoporous structure, which resulted in the carbon material with the highest of nitrogen content (4.08%) and the special surface area (1298.26 m²·g⁻¹). Specifically, the potential mechanisms of pore formation and N-doping in the one-pot dual-activation strategy were also proposed as a consequence, the one-pot dual-activated carbon material displayed excellent electrochemical performance with the highest capacitance of 309.5 F·g⁻¹ at 0.5 A·g⁻¹, and the unipolar specific capacitance remained with cyclic characteristics of 80.1% after 10,000 cycles in two-electrode symmetric system. Furthermore, the one-pot dual-activation strategy could create a profit of $1.64–$2.38 per kilogram of bio-tar processed without considering the initial investment and labor costs, which provides new perspectives for the utilization of waste bio-tar.

Numerous studies have unequivocally demonstrated that biochar and, to a lesser degree, earthworms can independently improve soil fertility and crop productivity, although information about their co-application effects on soil characteristics is limited. In this review, (1) earthworm biomarkers and underlying influencing factors, as well as the changes in the amended soil quality in response to co-application of earthworms and biochar are presented, (2) the functional interactions between earthworms and biochar in soil are summarized; (3) the principles governing the synergetic effects of biochar and earthworms on soil quality enhancement are probed; and (4) alternative strategies to optimize the efficacy of earthworm and biochar amendments are provided. It is noteworthy that while low doses of biochar can have a positive effect on various earthworm biomarkers, including growth and reproduction, restoration of the intestinal environment, and the mitigation of cellular organelle toxicity and genetic damage, high biochar dosages can yield adverse effects. Conversely, earthworms play a crucial role in distributing biochar particles deeper into the soil matrix, bolstering carbon sequestration potential, and enhancing the persistence and efficiency of biochar utilization. Moreover, earthworms stimulate the production of soil extracellular enzymes by microorganisms, which are pivotal to the processing, stabilization, and decomposition of soil organic matter, as well as nutrient cycling in terrestrial ecosystems. Additionally, they enhance the binding affinities of these enzymes to biochar. Significantly, changes in earthworm biomarkers in response to biochar integration are predominately governed by biochar properties and dosage, contact time, and soil type.

Biochar, as a potential CO₂ adsorbent, is of great significance in addressing the problem of global warming. Previous studies have demonstrated that the CO₂ adsorption performance of biochar can be improved by nitrogen and sulfur doping. Co-doping can integrate the structure and function of two elements. However, the physicochemical interaction of nitrogen and sulfur during doping and the CO₂ adsorption process remains unclear in co-doped biochar. In this study, the heteroatom-doped biochar was prepared with different additives (urea, sodium thiosulfate, and thiourea) via hydrothermal carbonization, and the physicochemical interaction of nitrogen and sulfur in co-doped biochar was investigated extensively. The findings revealed that nitrogen and sulfur competed for limited doped active sites on the carbon skeleton during the co-doping process. Interestingly, thiourea retained the amino group on the surface of biochar to a great extent due to carbon–sulfur double bond breaking and bonding, which facilitated the formation of pore in the activation process. Significantly, co-doping had no significant improvement effect although nitrogen and sulfur doping separately enhanced the CO₂ adsorption performance of biochar by 11.9% and 8.5%. The nitrogen-containing and sulfur-containing functional groups in co-doped biochar exhibited mutual inhibition in the process of CO₂ adsorption. The findings of this study will have pertinent implications in the application of N/S co-doped biochar for CO₂ adsorption.

Biochar has gained significant attention in agricultural and environmental research over the last two decades. This comprehensive review evaluates the effects of biochar on soil organic carbon (SOC), emission of non-CO₂ greenhouse gases, and crop yield, including related mechanisms and major influencing factors. The impacts of biochar on SOC, methane and nitrous oxide emissions, and crop yield are controlled by biochar and soil properties and management practices. High-temperature biochar produced from lignin-rich feedstocks may decrease methane and nitrous oxide emissions in acidic soils and strengthen long-term carbon sequestration due to its stable aromatic structure. In contrast, low-temperature biochar from manure may increase crop yield in low-fertility soils. Applying biochar to farmlands in China can increase SOC content by 1.9 Pg C and reduce methane and nitrous oxide emissions by 25 and 20 Mt CO₂-eq year⁻¹, respectively, while increasing crop yields by 19%. Despite the increasing evidence of the positive effects of biochar, future research needs to explore the potential factors that could weaken or hinder its capacity to address climate change and secure crop production. We conclude that biochar is not a universal solution for global cropland; however, targeted applications in fields, landscapes, or regional scales, especially in low fertility and sandy soils, could realize the benefits of biochar as a climate-smart measure.

Highlights

Icing of wind turbine blades will seriously hinder the development of the wind power industry, and the use of biomass resources to solve the icing problem is conducive to promoting the synergistic development of biomass and wind energy. In this study, ice-phobic coatings with photothermal and anti-corrosion properties were prepared by surface modification pyrolysis and hydrothermal reaction with rice straw biogas residue as raw material. The erosion of KOH and the surface modification of MoS₂ produced a rough structure of the material, and the high-temperature pyrolysis and hydrothermal reaction promoted the dehydrogenation and decarboxylation reactions, which reduced the number of oxygen-containing functional groups and  decreased the surface energy of the material. The ice-phobic coating has superhydrophobic properties with a contact angle of 158.32°. Due to the small surface area in contact with water, the coating was able to significantly reduce the icing adhesion strength to 53.23 kPa. The icing wind tunnel test results showed that the icing area and mass were reduced by 10.54% and 30.08%, respectively, when the wind speed was 10 m s⁻¹ and the temperature was − 10 °C. Photothermal performance tests showed that the MoS₂-loaded material  had light absorption properties, and the coating could rapidly warm up to 58.3 ℃ under xenon lamp irradiation with photothermal cycle stability. The loading of MoS₂ acts as a physical barrier, reducing the contact of corrosive media with the substrate, thus improving the anti-corrosion of the coating. This study has practical application value and significance for the development of the anti-icing field under complex environmental conditions.

The charosphere is a thin soil one surrounding the biochar with highly active biochemical functions. Yet, little is known about the spatial and temporal distribution of charosphere hotspots. In this study, repacked soil cores were incubated with a central layer of biochar (pristine or acid-modified) with or without nitrogen (N) additions for 30 days and sliced at the millimeter scale for analyzing soil pH, mineral N, bacterial and fungal communities as well as the putative functions. We aimed to determine gradient distributions (in millimeter scale) of charosphere affected by biochar under different N additions. Our results showed narrower gradient changes (3 mm) of microbial community composition and wider shifts (6 mm) in pH and inorganic N contents in charosphere. The pristine biochar increased the soil pH up to 1.5 units in the charosphere, and subsequently boosted the relative abundance of Proteobacteria, Acidobacteria, and Zygomycota. With N addition, both the biochar site and charosphere were observed with decreased complexity of microbial networks, which might imply the limited microbial functionality of charosphere. These results will advance the understanding and prediction of biochar’s environmental impacts in soil.

Pyrolysis is an effective technology for treating and utilizing biogas residue. To explore the phosphorus (P) supply capacity of the biochar generated from biogas residue of Eichhornia Crassipes, the P speciation of E. crassipes biogas residue and biomass during pyrolysis (300–700 °C) was analyzed by combining sequential chemical extraction, ³¹P nuclear magnetic resonance (NMR) and P K-edge X-ray absorption near edge structure (XANES) spectroscopy. Pyrolysis treatment promoted the conversion of amorphous Ca-P phases in biogas residue and biomass into crystalline hydroxyapatite (HAP) phase, which matched the formation of stable HCl-P pools in the biochar derived from biogas residue (AEBs, 22.65–82.04%) and biomass (EBs, 13.08–33.52%) in the process of pyrolysis. Moreover, the total P contents in AEBs (19.43–28.92 mg g⁻¹) were higher than that of EBs (3.41–5.26 mg g⁻¹), indicating that AEBs had a great P reclamation potential. The P release kinetics from AEBs and EBs in water were evaluated via an incubation experiment for 360 h. The P release from both AEBs and EBs conformed to the pseudo-second order kinetics model (R² > 0.93), but their P release behaviors were different. The P release of AEBs conformed to the diffusion-re-adsorption model, while that of EBs accorded with the diffusion-dissolution model. The diffusive gradients in thin-films (DGT) analysis showed that AEBs could significantly increase soil available P content as compared with EBs. Hence, the biochar produced from biogas residue of E. crassipes via pyrolysis has a good application potential as a P fertilizer.

Biochar wettability and ability to accumulate moisture inside the porous space are crucial for improving soil fertility, regulating soil water balance, and regulating nutrients. However, a long-term interaction of biochar with agricultural soils may drastically alter the wetting properties and, eventually, influence water holding capacity and the structure of soils. In this work, the structure and wetting properties of biochar samples after 6-year long exposure to a sandy loam Spodosol with a crop rotation and mineral fertilizers application were studied. It was found that the elemental composition of the aged biochars was richer and more "soil-like", which is explained by the presence of the mineral crust on the biochar surface. The temporal evolution of biochar in the soil without any mineral fertilizer application resulted in significant improvement of its surface wettability due to the effects of various environmental factors. The lateral surface of biochar after 6-year interaction with the soil changes into a loose porous layer in a form of grooved base filled with adherent mineral soil and clay particles. Contrary, the application of the mineral fertilizer to the soil resulted in decreased wettability of the biochar lateral surfaces due to a decrease in the polar component of surface energy and the crusting of the surface with fine material, which blocks the pore space of the biochar. As a result, water capacity of the biochar from the treatment with the fertilizer decreased compared to the biochar samples collected from the soil without the fertilizer application. The radial biochar surfaces of both types of samples collected from the soil were open vessels filled with soil particles that slow down complete wetting and water absorption. The treatment of the biochar samples with surfactants drastically increased wettability of lateral surface and water absorption capacity of control samples as compared to the samples collected from the soil. The obtained results support the idea that the hydrophilisation of biochar caused by the adhesion of soil particles and treatment of its pore surface with surfactants, can improve the water-holding capacity of the sandy loam Spodosol in the plant-available range of soil water.

Magnetite-functionalized biochar (MBC) is a promising engineered material for remediation of antibiotic-contaminated fields. However, sorption mechanisms of ionizable organic compounds such as sulfonamide antibiotics (SAs) on MBC are still unclear. This study employed four representative SAs including sulfamethazine (SMT), sulfamerazine (SMR), sulfadiazine (SDZ), and sulfamethoxazole (SMX), to compare the difference in sorption on MBC. Results showed that the sorption capacities and affinities of the four SAs varied with their substituents, hydrophobic properties, and dissociation constants (pK_a). Synergistic effect during co-pyrolysis with Fe³⁺ enhanced the sorption performance of MBC towards SAs compared to original BC. Spectral methods confirmed structural changes of MBC such as the variance in oxygen-containing groups and defective/graphitized phases. Results of modeling pH-dependent sorption revealed that H-bonding or π-bond assisted H-bonding determined the sorption affinities and capacities of SAs. In particular, the SAs with lower pK_a were thermodynamically favorable to form H-bonding with MBC via proton exchange with water molecules. Quantum calculation results quantified the contributions of H-bonding strengths and found that the energies of H-bonding were correlated with affinities of SAs. Moreover, contributions of oxygen-containing groups instead of minerals dominated the H-bonding energies. Mechanistic insights from this study can be valuable in exploring engineered BC composites for practical application in field remediation.

Biochar has a large specific surface area, well-developed pore structure, abundant surface functional groups, and superior nutrient supply capacity, which is widely available and environmentally friendly with its advantages in waste resource utilization, heavy metal(loid) remediation, and carbon storage. This review focuses on the interactions between biochar (including raw biochar, functional biochar (modified/ engineered/ designer biochar), and composite biochar) and rhizosphere during the remediation of soil contaminated with heavy metal(loid)s (Pb, As, Cd, Hg, Co, Cu, Ni, Zn, Cr, etc.) and the effects of these interactions on the microbial communities and root exudates (enzymes and low-molecular-weight organic acids (LMWOAs)). In terms of microorganisms, biochar affects the composition, diversity, and structure of microbial communities through the supply of nutrients, provision of microbial colonization sites, immobilization of heavy metal(loid)s, and introduction of exogenous microorganisms. With regard to root exudates, biochar provides electron transfer support between the microorganisms and exudates, regulates the secretion of enzymes to resist the oxidative stress stimulated by heavy metal(loid)s, ameliorates rhizosphere acidification caused by LMWOAs, and promotes the activity of soil enzymes. The roles and mechanisms of biochar on rhizosphere soils are discussed, as well as the challenges of biochar in the remediation of heavy metal(loid)-contaminated soils, and the issues that need to be addressed in future research are foreseen.

The extensive use of neonicotinoids on food crops for pest management has resulted in substantial environmental contamination. It is imperative to develop an effective remediation material and technique as well as to determine the evolution pathways of products. Here, novel ball-milled nitrogen-doped biochar (NBC)-modified zero-valent iron (ZVI) composites (named MNBC-ZVI) were fabricated and applied to degrading neonicotinoids. Based on the characterization results, NBC incorporation introduced N-doped sites and new allying heterojunctions and achieved surface charge redistribution, rapid electron transfer, and higher hydrophobicity of ZVI particles. As a result, the interaction between ZVI particles and thiamethoxam (a typical neonicotinoid) was improved, and the adsorption–desorption and reductive degradation of thiamethoxam and ·H generation steps were optimized. MNBC-ZVI could rapidly degrade 100% of 10 mg·L⁻¹ thiamethoxam within 360 min, its reduction rate constant was 12.1-fold greater than that of pristine ZVI, and the electron efficiency increased from 29.7% to 57.8%. This improved reactivity and selectivity resulted from increased electron transfer, enhanced hydrophobicity, and reduced accumulation of iron mud. Moreover, the degradation of neonicotinoids occurred mainly via nitrate reduction and dichlorination, and toxicity tests with degradation intermediates revealed that neonicotinoids undergo rapid detoxification. Remarkably, MNBC-ZVI also presented favorable tolerance to various anions, humic acid, wastewater and contaminated soil, as well as high reusability. This work offers an efficient and economic biochar-ZVI remediation technology for the rapid degradation and detoxification of neonicotinoids, significantly contributes to knowledge on the relevant removal mechanism and further advances the synthesis of highly reactive and environmentally friendly materials.

Applying biochar amendment and manure in tea plantation ecosystems can diminish soil acidification and degradation. However, the impact of these practices on soil respiration and associated mechanisms remains unclear. In this study, we combined a two-year field experiment and laboratory analyses based on soil properties, functional genes, and microbial co-occurrence networks to explore the determinants of soil respiration intensity in a subtropical tea plantation with biochar amendment and manure application. The results showed that the effect of biochar amendment on soil respiration was unconspicuous. Although biochar amendment increased bacterial richness and Shannon index, biochar amendment did not alter the abundance of species associated with C-cycling functional genes. Besides directly adding recalcitrant C to the soil, biochar also indirectly enhanced C sequestration by weakly increasing soil carbon dioxide (CO₂) emissions. However, replacing mineral fertilizer with manure significantly stimulated soil respiration in the tea plantation, resulting in a 36% increase in CO₂ emissions over two years. The increase in CO₂ emissions under the manure treatment was mainly attributed to the increased soil labile C pool, the activity of hydrolytic enzymes (e.g., cellobiohydrolase and acetylglucosaminidase), and the relative abundance of functional genes associated with the C-cycle. This may also be related to the application of manure that increased the abundance of Gemmatimonadetes and altered ecological clusters in bacterial co-occurrence networks. Our correlation network analysis suggested that Gemmatimonadetes might be the potential hosts for C-cycling genes due to their strong positive correlation with the abundance of C-cycling genes. Overall, these findings provide new insights into soil respiration under biochar amendment and manure application in tea plantations and broaden the options for carbon sequestration in soils.

Herein, we report the synthesis of interconnected hierarchical pore biochar (HTB) via an ice-templating strategy using bio-waste (tofukasu). The abundance of N- and O-containing functional groups in tofukasu makes it easy to form hydrogen bonds with water molecules and water clusters, resulting in nano-micro structures like ice clusters and snow crystals during freezing process. More importantly, tofukasu will be squeezed by micron-scale snow crystals to form coiled sheet-like structures, and its surface and interior will be affected by needle-like ice nanocrystals from several nanometers to tens of nanometers to form transverse groove needles and mesopores. The ice crystals are then removed by sublimation with tofukasu, leaving the interconnected pore structure intact. Therefore, the ice template synthesis strategy endowed the interconnected hierarchical pore structure of HTB with a large specific surface area (S_BET, 733 m²⋅g⁻¹) and hierarchical porosity (30.30% for mesopores/total pore volume ratio), which is significantly higher than the normal dry treated tofukasu biochar (TB), which had a S_BET of 436 m²⋅g⁻¹ and contained 1.53% mesopores. In addition, the sheet-like structure with interconnected pores of HTB favors high exposure of active sites (N- and O-containing functional groups), and a fast electron transport rate. As a result, HTB had an excellent adsorption capacity of 159.65 mg⋅g⁻¹, which is 4.7 times that of typical block biochar of TB (33.89 mg⋅g⁻¹) according to Langmuir model. Electrochemical characterization, FTIR and XPS analysis showed that the mechanism of Cr(VI) removal by HTB included electrostatic attraction, pore filling, reduction and surface complexation.

Metalloid pollution, including arsenic poisoning, is a serious environmental issue, plaguing plant productivity and quality of life worldwide. Biochar, a carbon-rich material, has been known to alleviate the negative effects of environmental pollutants on plants. However, the specific role of biochar in mitigating arsenic stress in maize remains relatively unexplored. Here, we elucidated the functions of biochar in improving maize growth  under the elevated level of sodium arsenate (Na₂AsO₄, As^V). Maize plants were grown in pot-soils amended with two doses of biochar (2.5% (B1) and 5.0% (B2) biochar Kg⁻¹ of soil) for 5 days, followed by exposure to Na₂AsO₄ ('B1 + As^V'and 'B2 + As^V') for 9 days. Maize plants exposed to As^V only accumulated substantial amount of arsenic in both roots and leaves, triggering severe phytotoxic effects, including stunted growth, leaf-yellowing, chlorosis, reduced photosynthesis, and nutritional imbalance, when compared with control plants. Contrariwise, biochar addition improved the phenotype and growth of As^V-stressed maize plants by reducing root-to-leaf As^V translocation (by 46.56 and 57.46% in ‘B1 + As^V’ and ‘B2 + As^V’ plants), improving gas-exchange attributes, and elevating chlorophylls and mineral levels beyond As^V-stressed plants. Biochar pretreatment also substantially counteracted As^V-induced oxidative stress by lowering reactive oxygen species accumulation, lipoxygenase activity, malondialdehyde level, and electrolyte leakage. Less oxidative stress in ‘B1 + As^V’ and ‘B2 + As^V’ plants likely supported by a strong antioxidant system powered by biochar-mediated increased activities of superoxide dismutase (by 25.12 and 46.55%), catalase (51.78 and 82.82%), and glutathione S-transferase (61.48 and 153.83%), and improved flavonoid levels (41.48 and 75.37%, respectively). Furthermore, increased levels of soluble sugars and free amino acids also correlated with improved leaf relative water content, suggesting a better osmotic acclimatization mechanism in biochar-pretreated As^V-exposed plants. Overall, our findings provided mechanistic insight into how biochar facilitates maize’s active recovery from As^V-stress, implying that biochar application may be a viable technique for mitigating negative effects of arsenic in maize, and perhaps, in other important cereal crops.

Drying and rewetting (DRW) events cause the release of colloidal phosphorus (P_coll, 1–1000 nm) in leachate, and biochar is considered an effective inhibitor; however, the microbial mechanism remains elusive. In this study, three successive DRW cycles were performed on the soil columns to assess the effect of biochar addition on P_coll content and its possible associates, including phosphatase-producing microbial populations (phoD- and phoC-harboring microbial communities) and alkaline/acid phosphatase (ALP/ACP) activities. Results showed that the biochar addition significantly decreased the P_coll by 15.5–32.1% during three DRW cycles. The structural equation model (SEM) confirmed that biochar addition increased phoD- and phoC-harboring microbial communities and ALP/ACP activities, which reduces the release of P_coll into leachate. In addition, the manure biochar was more effective than the straw biochar in promoting competition and cooperation in the co-occurrence network (2–5% nodes increased on average), and the key taxa Proteobacteria and Cyanobacteria were identified as the dominant species of potential ALP/ACP activities and P_coll content. Our findings provide a novel understanding of biochar reducing P_coll loss from the phosphatase perspective by regulating the phoD- and phoC-harboring communities during DRW events.

Due to the rising need for clean and renewable energy, green materials including biochar are becoming increasingly popular in the field of energy storage and conversion. However, the lack of highly active and stable electrode materials hinders the development of stable energy supplies and efficient hydrogen production devices. Herein, we fabricated stable, conductive, and multifunctional chitosan microspheres by a facile emulsion crosslinking solution growth and hydrothermal sulphuration methods as multifunctional electrodes for overall water splitting driven by supercapacitors. This material possessed three-dimensional layered conductors with favorable heterojunction interface, ample hollow and porous structures. It presented remarkably enhanced electrochemical and catalytic activity for both supercapacitors and overall water electrolysis. The asymmetric supercapacitors based on chitosan biochar microsphere achieved high specific capacitance (260.9 F g⁻¹ at 1 A g⁻¹) and high energy density (81.5W h kg⁻¹) at a power density of 978.4 W kg⁻¹. The chitosan biochar microsphere as an electrode for electrolyze only required a low cell voltage of 1.49 V to reach a current density of 10 mA cm⁻², and achieved excellent stability with 30 h continuous test at 20 mA cm⁻². Then, we assembled a coupled energy storage device and hydrogen production system, the SCs as a backup power source availably guaranteed the continuous operation of overall water electrolysis. Our study provides valuable perspectives into the practical design of both integrated biochar-based electrode materials and coupled energy storage devices with energy conversion and storage in practical.

Hydrothermal carbonization (HTC) technology has increasingly been considered for biomass conversion applications because of its economic and environmental advantages. As an HTC conversion product, hydrochar has been widely used in the agricultural and environmental fields for decades. A CiteSpace-based system analysis was used for conducting a bibliometric study to understand the state of hydrochar environmental application research from 2011 to 2021. Researchers had a basic understanding of hydrochar between 2011 and 2016 when they discovered hydrochar could apply to agricultural and environmental improvement projects. Keyword clustering results of the literature published in 2017–2021 showed that soil quality and plant growth were the major research topics, followed by carbon capture and greenhouse gas emissions, organic pollutant removal, and heavy metal adsorption and its bioavailability. This review also pointed out the challenge and perspective for hydrochar research and application, namely: (1) the environmental effects of hydrochar on soils need to be clarified in terms of the scope and conditions; (2) the influence of soil microorganisms needs to be investigated to illustrate the impact of hydrochar on greenhouse gas emissions; (3) combined heavy metal and organic contaminant sorption experiments for hydrochar need to be conducted for large-scale applications; (4) more research needs to be conducted to reveal the economic benefits of hydrochar and the coupling of hydrochar with anaerobic digestion technology. This review suggested that it would be valuable to create a database that contains detailed information on how hydrochar got from different sources, and different preparation conditions can be applied in the environmental field.

Crystal morphology of metal oxides in engineered metal-biochar composites governs the removal of phosphorus (P) from aqueous solutions. Up to our best knowledge, preparation of bio-assembled MgO-coated biochar and its application for the removal of P from solutions and kitchen waste fermentation liquids have not yet been studied. Therefore, in this study, a needle-like MgO particle coated tea waste biochar composite (MTC) was prepared through a novel biological assembly and template elimination process. The produced MTC was used as an adsorbent for removing P from a synthetic solution and real kitchen waste fermentation liquid. The maximum P sorption capacities of the MTC, deduced from the Langmuir model, were 58.80 mg g⁻¹ from the solution at pH 7 and 192.8 mg g⁻¹ from the fermentation liquid at pH 9. The increase of ionic strength (0–0.1 mol L⁻¹ NaNO₃) reduced P removal efficiency from 98.53% to 93.01% in the synthetic solution but had no significant impact on P removal from the fermentation liquid. Precipitation of MgHPO₄ and Mg(H₂PO₄)₂ (76.5%), ligand exchange (18.0%), and electrostatic attraction (5.5%) were the potential mechanisms for P sorption from the synthetic solution, while struvite formation (57.6%) and ligand exchange (42.2%) governed the sorption of P from the kitchen waste fermentation liquid. Compared to previously reported MgO-biochar composites, MTC had a lower P sorption capacity in phosphate solution but a higher P sorption capacity in fermentation liquid. Therefore, the studied MTC could be used as an effective candidate for the removal of P from aqueous environments, and especially from the fermentation liquids. In the future, it will be necessary to systematically compare the performance of metal-biochar composites with different metal oxide crystal morphology for P removal from different types of wastewater.

Biochar has various agricultural applications, including the promising use as a carrier for beneficial microorganisms. However, most recent research has demonstrated the possible attachment or immobilization of a single bacterial species onto biochar rather than a consortium of microbes for biotechnological applications. Thus, an assessment on the potential of oil palm kernel shell (OPKS) biochar as a biofilm-producing Bacillus consortium carrier through optimization study on the operating and environmental factors influencing the biofilm adhesion was conducted using response surface methodology (RSM) and the subsequent soil stability and storage potential of the formulation. The highest Bacillus population   was observed  at temperature  33 °C, agitation speed of 135 rpm, at a neutral pH of 7.5 with 10% (w/w) of sago starch as the co-carbon source. The adhesion of Bacillus on OPKS biochar following the optimized conditions fitted pseudo-second order (PSO) of kinetic modelling (R² = 0.998). The optimized formulation was subjected to storage in different temperatures and in vitro soil incubation which revealed that the Bacillus biofilm-adhered OPKS biochar may be stored up to 4 months with minimum range of live Bacillus viability reaching 10⁷ CFU g^-1 of biochar which is within the minimum range of acceptable biofertilizer viability (10⁶ CFU mL^-1). Formulation that is viable in room storage can be easily incorporated into current agricultural distribution networks that do not have refrigeration. This work highlighted the physicochemical and soil stability qualities of optimized Bacillus consortium adhesion on biochar for agricultural usage.

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