Biochar is a promising carbon dioxide removal (CDR) technology for climate change mitigation. Current procedures for its determination are lengthy, labor-intensive, and difficult to conduct. Benzene polycarboxylic acids (BPCA) are the most promising molecular markers for identification and quantification of biochar and its quality as they specifically represent the stable polyaromatic backbone of biochar. Therefore, using the BPCA method, its stability and, thus, its C sequestration potential could be used for CDR accounting. The current BPCA method relies on a specific high-pressure digestion apparatus, which is not available around the world. Therefore, the aims of the present work were (i) to compare the conventional high-pressure nitric acid oxidation with a microwave-assisted digestion technique and optimize the oxidation conditions in such a way that previous results are comparable with future ones, and (ii) to significantly reduce the digestion time of soil samples of 8 h and to develop a suitable routine method that produces comparable and reproducible results. For this purpose, soil and control sample series were prepared for different temperature–time-program. Obtained results were compared with the values of the conventional method both for individual samples and for the whole dataset separately. To ensure the representativeness of the results, in addition to various soil samples with different properties, we included two reference materials into our data set, one without biochar (wheat flour) and a biochar sample. Our results showed that conventional nitric acid oxidation in the BPCA determination at 170 °C and 8 h can be substituted by digestion in a microwave reaction system (CEM Mars6) at 190 °C and 1 h. Our results further showed that this condition needs to be strictly matched, because, otherwise, over- or underestimation of biochar quantity and/or quality will be the consequence. The goal of a less time-consuming BPCA extraction from soil samples was achieved by reducing the extraction time from 8 to 1 h using the microwave-assisted method. However, one disadvantage of the new method is that five times more sample material and chemicals are needed for further BPCA analysis, compared to the original method.
This study presents a scientometric analysis on biochar research to investigate the research status and developments as well as future trends in this field in 2020. A total of 3671 publications were retrieved from the Web of Science core collection database in 2020, which were analyzed for categories, countries, authors, and keywords. China and USA played a leading role in the research of biochar. Yong Sik Ok and Daniel C. W. Tsang were the most prolific authors in the application of biochar in agriculture, environment, and energy. Based on the keywords clustering analysis, biochar applications in “bioenergy production”, “global climate change mitigation”, “salinity and drought stress amelioration”, “organic pollutants degradation”, “heavy metals immobilization”, and “bioremediation” were the main hotspots. Biochar for salinity and drought stress amelioration became the focus in biochar area in 2020 as biochar amendment had great potential in alleviating salt- and drought-affected soils. Organic pollutants’ degradation via advanced oxidation process (AOPs) represents a sustainable growing topic. Radical and non-radical pathways were summarized for AOPs. Bioremediation using functional bacteria (e.g., heavy metal-resistant bacteria and organic pollutant-degraders) immobilized on biochar was still a research hotspot. Immobilized cells showed excellent performance in removing various contaminants by combining the advantages of highly efficient physiochemical sorption of biochar and microbial metabolisms. The review improves our understanding on scientific advances and potential future research directions in biochar research.
A number of processes for post-production treatment of “raw” biochars, including leaching, aeration, grinding or sieving to reduce particle size, and chemical or steam activation, have been suggested as means to enhance biochar effectiveness in agriculture, forestry, and environmental restoration. Here, I review studies on post-production processing methods and their effects on biochar physio-chemical properties and present a meta-analysis of plant growth and yield responses to post-processed vs. “raw” biochars. Data from 23 studies provide a total of 112 comparisons of responses to processed vs. unprocessed biochars, and 103 comparisons allowing assessment of effects relative to biochar particle size; additional 8 published studies involving 32 comparisons provide data on effects of biochar leachates. Overall, post-processed biochars resulted in significantly increased average plant growth responses 14% above those observed with unprocessed biochar. This overall effect was driven by plant growth responses to reduced biochar particle size, and heating/aeration treatments. The assessment of biochar effects by particle size indicates a peak at a particle size of 0.5–1.0 mm. Biochar leachate treatments showed very high heterogeneity among studies and no average growth benefit. I conclude that physiochemical post-processing of biochar offers substantial additional agronomic benefits compared to the use of unprocessed biochar. Further research on post-production treatments effects will be important for biochar utilization to maximize benefits to carbon sequestration and system productivity in agriculture, forestry, and environmental restoration.
Biochars, when applied to contaminated solutions or soils, may sequester potentially toxic elements while releasing necessary plant nutrients. This purpose of this study focused on quantifying both phenomenon following wheat straw (Triticum aestivum L.) biochar application (0, 5, and 15% by wt) to a Cd containing solution and a Cd-contaminated paddy soil using 240-day laboratory batch experiments. Following both experiments, solid phases were analyzed for elemental associations using a combination of wet chemical sequential extractions and synchrotron-based X-ray absorption spectroscopy (XAS). When wheat straw biochar was applied at 15% to Cd containing solutions, Cd and Zn concentrations decreased to below detection in some instances, Ca and Mg concentrations increased by up to 290%, and solution pH increased as compared to the 5% biochar application rate. Similar responses were observed when biochar was added to the Cd-contaminated paddy soil, suggesting that this particular biochar has the ability to sequester potentially toxic elements while releasing necessary plant nutrients to the soil solution. When significant, positive correlations existed between nutrient release over time, while negative correlations were present between biochar application rate, potentially toxic element sorption and pH. The latter suggests that potentially toxic elements were sorbed by a combination of organic functional groups or mineral precipitation based on whether pH was above or below ~ 7. In support of this contention, the wet chemical sequential extraction procedure in conjunction with previously observed Cd or current Zn XAS showed that biochar application promoted the formation of layered double hydroxides, sorption to (oxy)hydroxides, and organically bound to biochar as Zn species. As a multi-functional material, biochar appears to play an important role in sequestering Cd while releasing essential plant nutrients. These findings suggest that biochar may be a ‘win–win’ for improving environmental quality in potentially toxic element contaminated agroecosystems.
Recent studies have shown that silicon (Si) dissolution from biochar may be influenced by the pyrolysis temperature. In addition, the enhancement of biochar by treatment with alkali has been proposed to produce a Si source that can be used for environmentally friendly plant disease control. In this study, biochars from rice straw and rice husk pretreated with KOH, CaO and K2CO3 and then pyrolyzed at 350, 450 and 550 °C were prepared to evaluate the effects of pyrolysis temperature on Si release and plant uptake from alkali-enhanced Si-rich biochar. Extractable Si and dissolution Si from the prepared biochars were assessed by different short-term chemical methods and long-term (30-day) release in dilute acid and neutral salt solutions, respectively, along with a rice potting experiment in greenhouse. For both rice straw- and husk-derived alkali-enhanced biochars (RS-10KB and HS-10K2B, respectively), increasing the pyrolysis temperature from 350 to 550 °C generally had the highest extractable Si and increased Si content extracted by 5-day sodium carbonate and ammonium nitrate (5dSCAN) designated for fertilizer Si by 61–142%, whereas non-enhanced biochars had more extractable Si at 350 °C. The alkali-enhanced biochars produced at 550 °C pyrolysis temperature also released 82–172% and 27–79% more Si than that of 350 °C produced biochar in unbuffered weak acid and neutral salt solutions, respectively, over 30 days. In addition, alkali-enhanced biochars, especially that derived from rice husk at 550 °C facilitated 6–21% greater Si uptake by rice and 44–101% higher rice grain yields than lower temperature biochars, non-enhanced biochars, or conventional Si fertilizers (wollastonite and silicate calcium slag). Overall, this study demonstrated that 550 °C is more efficient than lower pyrolysis temperature for preparing alkali-enhanced biochar to improve Si release for plant growth.
Soil amendment with biochar alleviates the toxic effects of heavy metals on microbial functions in single-metal contaminated soils. Yet, it is unclear how biochar application would improve microbial activity and enzymatic activity in soils co-polluted with toxic metals. The present research aimed at determining the response of microbial and biochemical attributes to addition of sugarcane bagasse biochar (SCB) in cadmium (Cd)-lead (Pb) co-contaminated soils. SCBs (400 and 600 °C) decreased the available concentrations of Cd and Pb, increased organic carbon (OC) and dissolved organic carbon (DOC) contents in soil. The decrease of metal availability was greater with 600 °C SCB than with 400 °C SCB, and metal immobilization was greater for Cd (16%) than for Pb (12%) in co-spiked soils amended with low-temperature SCB. Biochar application improved microbial activity and biomass, and enzymatic activity in the soils co-spiked with metals, but these positive impacts of SCB were less pronounced in the co-spiked soils than in the single-spiked soils. SCB decreased the adverse impacts of heavy metals on soil properties largely through the enhanced labile C for microbial assimilation and partly through the immobilization of metals. Redundancy analysis further confirmed that soil OC was overwhelmingly the dominant driver of changes in the properties and quality of contaminated soils amended with SCB. The promotion of soil microbial quality by the low-temperature SCB was greater than by high-temperature SCB, due to its higher labile C fraction. Our findings showed that SCB at lower temperatures could be applied to metal co-polluted soils to mitigate the combined effects of metal stresses on microbial and biochemical functions.
The application of Fe–Mn-modified biochar for the remediation of Cd-contaminated soil over long time periods has been little studied. In this paper, we describe the performance of coconut-shell-derived biochar modified with ferromanganese in relation to soil Cd stabilization and rice Cd bioaccumulation during a 3-year laboratory study. Different application dosages (0.05–0.5 wt%) and different rice varieties (the early and late rice) are also considered. The results show that ferromanganese is mainly loaded in biochar pores as MnFe2O4, and that it decreases the specific surface area (SSA) and total pore volume of biochar. Ferromanganese biochar (0.5 wt%) applied to paddy soil is more effective than the same dose of pristine biochar in decreasing the soil-exchangeable Cd fraction (27.42–41.92% vs 22.56–33.85%), predominantly by decreasing soil Eh and increasing root Fe plaques. Ferromanganese biochar application helps to reduce Cd bioaccumulation in rice, especially in the grain (up to 48.6%–61.0%), and grain Cd levels (0.2 mg/kg) are all within the acceptable limit for food security in China. It is shown that ferromanganese modification and application can maintain soil at low redox status, keep root Fe plaques at a high level, and may also increase the stability of pristine biochar. All of these effects contribute to maintaining its high remediation efficiency over a 3-year inoculation period. The results presented in this paper demonstrate the potential applications of ferromanganese biochar in soil remediation and the improvement of food safety.
Cadmium (Cd) and lead (Pb) contaminated soils that are used for food production can lead to metal bioaccumulation in the food chain and eventually affect human health. In these agroecosystems, means by which Cd and Pb bioavailability can be reduced are desperately required, with biochar as a proxy for bioavailability reductions. Molecular Cd and Pb sorption mechanisms within short- (0–2 years) or long-term (8–10 years) time periods following biochar application to a contaminated rice paddy soil were investigated. A combination of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and soft X-ray imaging was utilized to discern potential metal sorption mechanisms. Following both short- and long-term biochar applications, soil Cd and Pb bioavailable fractions shifted partially towards metal (hydr)oxide and carbonate precipitates, and partially towards biochar-organic function group associations; oxygen-containing groups, such as C=O and O–H, appeared to bind Cd and Pb. Soft X-ray imaging results suggested that heavy metals were primarily sorbed on biochar exterior surfaces, yet given time and particle disintegration, metals sorbed onto biochar interior pore walls. Findings suggest that biochar may play a pivotal role in reducing long-term bioavailable Cd and Pb in contaminated soils. Observations also support previous findings that suggest biochar use can lead to reduced heavy metal transfer to plants and potentially to reduced heavy metal consumption by humans.
Mining and excavation activities cause massive degradation of land, leading to complete loss of soil resources, vegetation, and biodiversity. Mine spoils support invasive weeds (predominantly Lantana) which can strive in these harsh conditions, causing allelopathy during plantation stage of reclamation. It is hypothesised that biochar produced from invasive weeds will enhance enzymatic activity, CO2 flux and overall fertility of coal mine spoil. A 6-month incubation study was conducted on the effect of biochar amendment (2 and 3%, w/w) on mine spoil enzymatic activities (dehydrogenase, invertase, amylase and cellulase), respiration and coal mine spoil fertility. The study showed that biochar significantly improved dehydrogenase (83%) and cellulase activity (78%) at 3% amendment. Geometric mean of enzymatic activities increased from 1.87 in control to 4.51 at 2% and 3.25 at 3% biochar amendment. Mine spoil physio-chemical properties such as soil organic carbon (65%), cation exchange capacity (54%), bulk density (25%) and water holding capacity (19%), were improved significantly compared to the unamended mine spoil. Biochar amendment reduced mine spoil CO2 flux at 2% (2.85 μmol CO2 m−2 s−1) and 3% (2.60 μmol CO2 m−2 s−1) compared to control (4.92 μmol CO2 m−2 s−1). The cost of biochar production and application (2%, w/w) in pit plantation during reclamation is estimated to be 844 USD t ha−1 (plantation density: 1600 trees ha−1). On the basis of present study, biochar preparation from invasive weeds can be used for sustainable reclamation of coal mine spoil.
A batch experiment was conducted to examine the effects of biochar dose and reaction duration on the transformation and immobilization of Cr(VI) in the combined biochar and low-molecular-weight organic acid systems. The results showed that increase in the dosage level of biochar caused increase in the solution pH, particularly for the Biochar300 treatments but did not enhance the reduction of Cr(VI) after 1-day reaction. Over 35% of the converted Cr(III) was immobilized by sorption to the biochar due to increased negatively charged sites on the biochar surfaces driven by pH rise. The elevated pH due to biochar dose increase tended to slow down the reduction of Cr(VI) to Cr(III), resulting in more Cr(VI) being adsorbed at a higher biochar dose. For the higher-temperature biochars, the increase in biochar dose did not markedly change the transformation and immobilization of the added Cr. Increase in the reaction duration markedly increased the pH for Biochar300. This resulted in the disappearance of all Cr(VI) in the solution after the 7-day reaction, possibly through sorption of cationic Cr(III) to the biochar surfaces. Increase in reaction time for the higher-temperature biochars resulted in re-oxidation of Cr(III) to Cr(VI) due to the increased exposure of solution Cr(III) to atmospheric oxygen. The research findings obtained from this study have implications for optimizing treatment procedure for wastewater that contains elevated level of toxic Cr(VI). Simulation experiments are required to determine appropriate biochar dose and reaction time to achieve cost-effective treatment goals.
Pesticide residues have seriously damaged the natural environment and social security. Here, we prepared the efficient functional biochar (FB) for sulfonylurea herbicides from cotton straw cellulose (CSC) by hydrothermal carbonization with the methacrylic acid. The molecular simulation of FB indicated that π-π electron-donor–acceptor (EDA) interaction and formation of charge-assisted H-bond were both the main factors for effective adsorption process. The adsorption process can match the pseudo-second-order kinetic equation and Freundlich model. The whole process is physical adsorption, spontaneous and rapid, and can quickly reach equilibrium. The FB with carbon–oxygen functional groups and aromatic conjugated structures can remove pesticides in water very quickly (within 30 s), with effective adsorption over 95% of Sulfonylurea herbicides (SUHs). Therefore, functional FB might be an effective way to get excellent absorbent for pesticide treatment.
The purpose of this paper was to study the effects of different C/N ratios on the maturity and microbial quantity of composting with sesame meal and rice straw biochar. Rice straw was calcined into biochar as raw materials composting with sesame meal for 30 days, referring to Chenfu Agricultural Book in Sōuthern Song Dynasty (1127–1279 A.D.). Sesame meal was used to adjust the C/N ratio of compost, and three treatments were designed in the experiment, which were C/N ratios of 15, 20 and 30, respectively. The results showed that C/N ratio of 20 was beneficial for promoting the temperature rise, the removal of water, the degradation of organic carbon, and the decrease of microbial quantity. The C/N ratio of 20 was beneficial to the compost maturity (T value was 0.47, final GI was 99.67%). The results of Pearson correlation analysis showed that C/N ratio was positively correlated with moisture content, total organic carbon and negatively correlated with germination index, indicating that high C/N ratio was beneficial to water removal and total organic carbon degradation. Therefore, we suggest that the suitable C/N ratio of rice straw biochar and sesame meal is 20. At the same time, we have proved that the composting method in Southern Song Dynasty is feasible, which is of great significance to understand the development of composting in China.
In response to increasing concerns over climate change, soil health and wine quality, grape growers are seeking new practices (e.g., biochar application) to minimize their environmental footprint while increasing productivity and the quality of their products. To explore the potential of biochar-based amendments to achieve these goals in wine grape production, vineyard trials were established in the fall of 2018. Two Oregon sites were chosen with distinct soil types and climates (Willamette Valley and Rogue Valley) but planted with the same grapevine scion/rootstock Pinot noir combination. Four treatments were applied under vines at each location: no biochar-no tillage (NT); no biochar + tillage (B0); 18 tons ha−1 biochar + tillage (B18); 35 tons ha−1 biochar + tillage (B35). In 2019, a suite of soil health, plant, and crop variables were measured, and wines were produced after harvest. The incorporation of biochar modified the chemical and physical composition of soils at the two studied locations, increasing the bioavailability of carbon and nitrogen, their gravimetric water content and the concentration of plant available micro and macro nutrients. No responses of plant physiology parameters or productivity at either site were found after biochar incorporation when compared with controls. Conversely, a significant and gradual decrease in the amount of wine tannins was found as a result of biochar application in wines produced from grapes from the Woodhall location. Long-term field experiments are required to assess the effects of biochar on soil properties, vine physiology, productivity, and grape and wine quality several years after incorporation.
To explore the effect of biochar on alleviating plant drought stress after being applied to soil, we prepared biochar using rice straw as raw material according to different pyrolysis temperatures (400, 600 and 800 °C) and reaction atmosphere (CO2 and N2). The effect of different pyrolysis conditions on the water retention performance of biochar was studied. The early high water-retaining biochar materials were selected and wheat seeds were selected for the verification experiment of returning to the field in pots. Biochar with high porosity (specific surface area and total pore volume) and more surface hydrophilic functional groups (mainly –OH and –COOH) can indeed improve soil water retention performance. It is mainly reflected in the increase in the dry weight and fresh weight of wheat and the soil moisture content in the treatment group with the addition of biochar water retention agent. Among them, the growth rates of fresh weight and dry weight of wheat in the C800 treatment group were 11.51% and 10.64%, and the soil moisture content increased by 1.89%. It is worth noting that the application of biochar cannot completely alleviate the impact of drought stress on plants, but it can reduce the amount of water irrigation to a certain extent. Considering the quality of biochar, the biochar material (C800) prepared under the pyrolysis temperature of 800 °C and the reaction atmosphere of CO2 has high water retention performance.
Poultry litter biochar is known to improve crop productivity. However, its beneficial interactions with chemical fertilizer and/or organic manure on rice yield and nitrogen (N) use efficiency (NUE) are not well studied. The objective of this study was to co-apply poultry litter biochar (hereinafter biochar) and chemical fertilizer and/or Azolla as organic manure (herein N fertilizer sources) to improve the productivity of rice and NUE. Eight treatments—no amendments (control), chemical fertilizer (NPK), Azolla as green manure (Azolla), and NPK + Azolla without and with biochar amendment—were evaluated in a pot trial. Selected rice plant growth components, yield, and NUE were determined. Compared to the treatments without biochar, co-application of biochar and N fertilizer sources significantly improved grain N uptake by 23.9% and NUE by 34.3–246.9%. These treatments also significantly improved rice growth components (5.6–18.2%) and grain yield (32.4%). Significant changes in soil properties including increases in pH, electrical conductivity (EC), total N, organic carbon, and available phosphorus were observed following biochar application. Except for the soil pH and EC parameters, no significant synergistic interactions between biochar and N fertilizer sources were observed for any parameters in the present study. Notably, compared to other treatments, the co-application of biochar and Azolla offers a feasible approach to improve rice productivity and NUE and reduce chemical fertilizer use, thereby reducing agricultural pollution and production costs.
Biochar has been considered as a potential way to enhance acidophilous plant growth in alkaline soils. However, whether such enhancements are closely linked with biochar pyrolysis temperature and its improvements in rhizospheric soil fertility and microbial activities remains largely unknown. We performed a pot experiment to investigate changes in azalea (Rhododendron) morphology and physiology, as well as its rhizosphere soil chemical and biological properties in a slightly alkaline urban soil under the amendment of biochars that pyrolyzed at three temperatures (i.e., 350, 550 and 700 °C). Our results showed that the effects of biochars on plant growth and soil properties depended on pyrolysis temperature. In comparison with the non-amended control, 350 and 550 °C biochars showed significant promotions on the azalea growth in terms of photosynthetic characteristics, biomass, root morphology, and N and P uptake. Whereas, 700 °C biochar showed an inhibition effect on them. 350 °C biochar decreased soil pH and increased soil available P and K contents and the activities of α-glucosidase, N-β-glucosaminidase, phosphatase and sulfatase. In addition, 350 °C biochar significantly enhanced bacterial 16S rRNA and fungal 18S rRNA gene abundances in the rhizosphere soil of azalea and mycorrhizal infection. Correlation analysis indicated that soil pH, available nutrients and fungal abundance had positive associations with the enhanced plant growth parameters. Therefore, our findings suggest that biochar produced at low temperature could be a feasible strategy for enhancing acidophilous azalea growth and improving urban soil quality.
Terrestrial and aquatic ecosystems are increasingly threatened by pesticide pollution resulting from extensive use of pesticides, and due to the lack of regulatory measures in the developing world, there is a need for affordable means to lessen environmental effects. This study aimed to investigate the impact of biochar amendment on the toxicity of imidacloprid to life-cycle parameters and biomarker responses of the earthworm Eisenia fetida. E. fetida was exposed to 10% biochar-amended and non-amended OECD artificial soils spiked with 0, 0.75, 1.5, 2.25 and 3 mg imidacloprid/kg for 28 days. An LC50 of 2.7 mg/kg was only computed in the non-amended soil but not in the biochar-amended soil due to insignificant mortality. The EC50 calculated in the non-amended soil (0.92 mg/kg) for reproduction (fertility) was lower than the one computed in the biochar amended (0.98 mg/kg), indicating a decrease in toxicity in the biochar-amended substrate. Significant weight loss was observed at the two highest imidacloprid treatments in the non-amended soil and only at the highest treatment in the biochar-amended substrate, further highlighting the beneficial effects of biochar. Catalase activity decreased significantly at the two highest concentrations of non-amended soil. Yet, in the amended soil, the activity remained high, especially in the highest concentration, where it was significantly higher than the controls. This indicated more severe oxidative stress in the absence of biochar. In all non-amended treatments, there was a significant acetylcholinesterase inhibition, while lower inhibition percentages were observed in the biochar-amended soil. In most endpoints, the addition of biochar alleviated the toxic effects of imidacloprid, which shows that biochar has the potential to be useful in soil remediation. However, there is still a need for field studies to identify the most effective application rate of biochar for land application.
Biochar, a known soil amendment, has been found to alleviate plant or soil-borne diseases. However, the related mechanisms are poorly understood, especially from the perspective of microbes colonizing in raw biochar. In this study, laboratory studies, including isolation, adsorption, antifungal test, were employed to investigate biological characteristic of a fungus isolated from aging biochars (peanut shell biochar, rice husk biochar and bamboo biochar), as well as antimicrobial mechanisms on Fusarium species which cause wheat crown rot and Fusarium head blight (FHB). Furthermore, the field trial was conducted to investigate the effect of this fungus on spikelet disease rate and crop yield. The results were as follows: the isolated fungus was identified as Papiliotrema flavescens (P. flavescens), which was confirmed from ambient air, and its properties were characterized, such as the optimal growth pH and the growth curve. The mixed action of 1 × 106 cells/mL P. flavescens and 1 × 106 cells/mL Bacillus subtilis (B. subtilis) had the best antifungal effect, reaching an antifungal rate of 86.5%. The P. flavescens exerted antifungal effects through potential competition among nutrition, space, and parasitism, not from producing antifungal substances. Results from the field trial showed that the presence of P. flavescens could reduce the spike disease rate by 43.2% and increase the yield by 34.5%. In summary, the present study provides novel evidence about microbes from aging biochars that can prevent wheat crown rot and FHB.
This study addressed a comparative assessment of the effect of low-cost catalysts on the yield and physicochemical properties of bio-oil. Thermal and catalytic pyrolysis of neem seeds (NM) was conducted in a fixed bed semi-batch reactor at optimum conditions (550 °C temperature, 80 °C min−1 heating rate, 0.5 mm particle size, and 100 mL min−1 sweep gas flow rate). The produced bio-oil and biochar were characterized through thermal stability, elemental composition (CHNS), higher heating value (HHV), Nuclear Magnetic Resonance (NMR) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), Gas Chromatography-Mass Spectrometry (GC–MS), zeta potential, water-holding capacity (WHC), and BET (Brunauer, Emmett and Teller) surface area analyzer. Overall, it was noticed that the use of catalysts at optimized condition substantially boosted the quality and yield of bio-oil. Pyrolysis results established that thermal pyrolysis yielded 49.53 wt.% of bio-oil, while catalytic pyrolysis yielded (51.25 wt.%, 53.12 wt.%, 48.68 wt.%, and 50.65 wt.% for MgO, NaOH, Al2O3, and ZSM-5, respectively) at 20 wt.% catalyst loading. The physicochemical study of bio-oil confirmed improved properties of bio-oil in terms of viscosity, heating value, pH and carbon content. Further, the FTIR study of bio-oil indicates the occurrence of phenolic products, aromatics, ketones, acidic compounds, esters, alcohol and aldehyde impurities, whereas 1H NMR study supported FTIR findings. GC–MS study demonstrated that the introduction of catalysts significantly reduced the oxygenated substances, acidic products, phenolic compounds and substantially increased the hydrocarbons. Further, characterization results of neem seed biochar (NMC) established the existence of HHV (23.26 MJ kg−1), carbon content (62.66%), zeta potential (31.68 mV), water holding capacity (41.50%) and lower BET surface area (4.60 m2 g−1).
Biochar obtained from a biomass pyrolytic polygeneration technology exhibits great potential as an adsorbent, because of its renewability, porosity and desirable surface chemical properties. Pyrolysis temperature and feed are important elements in the preparation of biochar. Thus, the effects of these factors on the physicochemical properties of biochar were investigated in this study. The adsorption of biochar was evaluated using water, CO2, phenol, and methylene blue (MB) as adsorbates. The correlation between adsorption capacity and physicochemical properties was determined using the Pearson correlation. Results indicated that temperature could significantly affect the structure of biochar. The effects of biomass species were also noticeable as well. The number of macropores and their contribution to the total surface area for cotton stalk, bamboo, and rapeseed stalk increased with an increase in temperatures, meanwhile, the number of micropores decreased at high temperatures. At the same temperature, the macropore, mesopore, and micropore components of biochar produced by different species were markedly different. The water adsorption and CO2 adsorption of biochar were close to those of commercial activated carbon (AC), whereas the adsorption capacity of untreated biochar on phenol and MB was less than that of AC. Porosity exerted more significant effects on the adsorption capacity of biochar, compared with functional groups. The surface area of the micropores exhibited a significant positive correlation with the adsorption of CO2, phenol, and MB. The hydroxyl group was positively correlated with water adsorption.
Biochar pores in the micrometer range (1–100 µm) derive from cellular structures of the plant biomass subjected to pyrolysis or can be the result of mechanical processing, such as pelleting. In this study, synchrotron X-ray microtomography was used to investigate the internal pore structure of softwood pellet biochar produced by slow pyrolysis at 550 and 700 °C. The microtomographic data sets consisted of 2025 images of 2560 × 2560 voxels with a voxel side length of 0.87 µm. The three-dimensional reconstructions revealed that pelleting and pyrolysis significantly altered the pore structures of the wood feedstock, creating a network of connected pores between fragments that resembled the wood morphology. While higher pyrolysis temperature increased the specific surface area (as determined by BET nitrogen adsorption), it did not affect the total observed porosity. Multifractal analysis was applied to assess the characteristics of the frequency distribution of pores along each of the three dimensions of reconstructed images of five softwood pellet biochar samples. The resulting singularity and Rényi spectra (generalized dimensions) indicated that the distribution of porosity had monofractal scaling behavior, was homogeneous within the analyzed volumes and consistent between replicate samples. Moreover, the pore distributions were isotropic (direction-independent), which is in strong contrast with the anisotropic pore structure of wood. As pores at the scale analyzed in this study are relevant, for example, for the supply of plant accessible water and habitable space for microorganisms, our findings combined with the ability to reproduce biochar with such pore distribution offer substantial advantages in various biochar applications.
Biochar has trigged increasing attention in the last decade due to its multiple functionalities, in which, color is not only the visual appearance, but also a useful indicator of relevant properties as well as an important tool to predict biochar’s properties. However, biochar color characterization remains challenged currently. In this work, three different feedstock-derived biochars were produced and basic color information (from color spaces RGB, HSB and CIE L*a*b*) of their scanned images was extracted. Then principal component analysis (PCA) and nonmetric multidimensional scaling analysis (NMDS) were employed on the combinations of different color indexes to cluster biochars. With the assumption that clusters from both PCA and NMDS were as consistent as possible with that of visual intuition of biochar color, we identified feedstock-independent color indexes [(R + G-B)/(R + G + B), (R + B-G)/(R + G + B), (G + B-R)/(R + G + B), L, a, b] to characterize color of biochar, which can in microscopic perspective elucidate color differences with respect to pyrolysis temperature and feedstock type. Finally, prediction ability of color indexes with biochar yield as model property was explored and good performance was observed for both partial least squares regression (R2 = 0.8653) and neural network regression (R2 = 0.9720) with the latter being more powerful. The proposed color indexes will find more applications in prediction of biochar properties and functions in future.
Porous carbon aerogel material has gained an increasing attraction for developing supercapacitor electrodes due to its cost-effective synthesis process and relatively high electrochemical performance. However, the environmental performances of supercapacitor electrodes produced from different carbon aerogel materials are never comparatively studied, hindering our knowledge of supercapacitor electrode production in a sustainable pattern. In this study, nitrogen-doped biochar aerogel-based electrode (BA-electrode) produced from Entermorpha prolifera was simulated to investigate the environmental performance by using life cycle assessment method. For comparison, the assessment of graphene oxide aerogel-based electrode (GOA-electrode) was also carried out. It can be observed that the life cycle global warming potential for the BA-electrode was lower than that of GOA-electrode with a reduction of 53.1‒68.1%. In comparison with GOA-electrode, the BA-electrodes endowed smaller impacts on environment in majority of impact categories. Moreover, in comparison with GOA-electrode, the environmental damages of BA-electrode were greatly decreased by 35.8‒56.4% (human health), 44.9‒62.6% (ecosystems), and 87.0‒91.2% (resources), respectively. The production stages of GOA and graphene oxide and stages of nitrogen-doped biochar aerogel production and Entermorpha prolifera drying were identified as the hotspots of environmental impact/damage for the GOA-electrode and BA-electrode, respectively. Overall, this finding highlights the efficient utilization of algae feedstock to construct a green and sustainable technical route of supercapacitor electrode production.