Metalloid co-contamination such as arsenic (As) and antimony (Sb) in soils has posed a significant threat to ecological balance and human well-being. In this study, a novel magnetic graphene-loaded biochar gel (FeBG) was developed, and its remediation potential for the reclamation of AsSb spoiled soil was assessed through a six-month soil incubation experiment. Results showed that the incorporation of iron substances and graphene imparted FeBG with enhanced surface characteristics, such as the formation of a new FeO bond and an enlarged surface area compared to the pristine biochar (BC) (80.5 m(2) g(-1) vs 57.4 m(2) g(-1)). Application of FeBG significantly decreased Na2HPO4-extractable concentration of As in soils by 9.9 %, whilst BC addition had a non-significant influence on As availability, compared to the control. Additionally, both BC (8.2 %) and FeBG (16.4 %) treatments decreased the Na2HPO4-extractable concentration of Sb in soils. The enhanced immobilization efficiency of FeBG for As/Sb could be attributed to FeBG-induced electrostatic attraction, complexation (Fe-O(H)-As/Sb), and pi-pi electron donor-acceptor coordination mechanisms. Additionally, the FeBG application boosted the activities of sucrase (9.6 %) and leucine aminopeptidase (7.7 %), compared to the control. PLS-PM analysis revealed a significant negative impact of soil physicochemical properties on the availability of As (beta = -0.611, P < 0.01) and Sb (beta = -0.848, P < 0.001) in soils, in which Sb availability subsequently led to a suppression in soil enzyme activities (beta = -0.514, P < 0.01). Overall, the novel FeBG could be a potential amendment for the simultaneous stabilization of As/Sb and the improvement of soil quality in contaminated soils.

This study examined the effectiveness of pristine biochar (BC) and Fe-functionalized biochar (FBC) in remediating As-Sb co-contaminated soil, and revealed the resulting impact on soil enzymatic activities and bacterial communities. Results from incubation experiments showed that the 1.5% FBC treatment reduced the bioavailable As and Sb concentration by 13.5% and 27.1%, respectively, in compared to the control, and reduced the proportion of specifically adsorbed and amorphous Fe-Mn oxide-bound metal(loid) fractions in the treated soil. Among the BC treatments, only the 1.5% BC treatment resulted in a reduction of bioavailable As by 11.7% and Sb by 21.4%. The 0.5% BC treatment showed no significant difference. The FBC achieved high As/Sb immobilization efficiency through Fe-induced electrostatic attraction, π-π electron donor-acceptor coordination, and complexation (Fe-O(H)-As/Sb) mechanisms. Additionally, the 1.5% FBC treatment led to a 108.2% and 367.4% increase in the activities of N-acetyl-β-glucosaminidase and urease in soils, respectively, compared to the control. Furthermore, it significantly increased the abundance of Proteobacteria (15.2%), Actinobacteriota (37.0%), Chloroflexi (21.4%), and Gemmatimonadota (43.6%) at the phylum level. Co-occurrence network analysis showed that FBC was better than BC in increasing the complexity of bacterial communities. Partial least squares path modeling further indicated that the addition of biochar treatments can affect soil enzyme activities by altering soil bacterial composition. This study suggests that FBC application offers advantages in simultaneous As and Sb immobilization and restructuring the bacterial community composition in metal(loid)-contaminated soil.

Environmental contamination posed by trivalent antimony [Sb(III)] in water has been globally recognized as a complex challenge, garnering considerable public concern. To enhance the adsorption efficiency of pristine biochar (BC) for Sb(III), a novel Fe/graphene-loaded biochar (FeGB) gel was synthesized through a facile in-situ self-assembly method. This study aimed to investigate the adsorption performance and elucidate the electronscale adsorption mechanism for Sb(III) by the FeGB-gel. The Sb(III) adsorption isotherm data fitted well with the Langmuir model, and the maximum Sb(III) adsorption capacity of FeGB-gel (113.1 mg g-1) was significantly higher compared to that of BC (28.6 mg g-1). Spectroscopic investigations revealed that surface complexation and 7C-7C stacking were the key mechanisms for Sb(III) adsorption. Electrochemical analyses confirmed an enhanced electron-accepting capacity (0.815 mmol e- g- 1) of FeGB-gel, linked to the formation of Fe-related functional groups (Fe-O and Fe-O-OH), which contributed to a stronger Sb(III) oxidation capacity than BC (78.5% v.s. 49.3%). Density functional theory calculations highlighted that the presence of defects on graphene nanosheets enhanced the anchoring of FeOx on biochar, thereby elevating the Sb(III) adsorption energy of FeGBgel to -1.96 eV. Additionally, the projected density of states profile suggested that the enhanced adsorption of FeGB-gel could be attributable to the orbital hybridization of Sb-p, O-p, and Fe-p/d orbitals (i.e., Fe-O-Sb bonding), which strengthened the electron transfer and chemical interaction during the Sb(III) removal process. The functionalization of biochar surface characteristics with Fe/graphene offers possibilities for a diverse range of biochar-based adsorbents and their application in addressing numerous environmental concerns.

Biochar is derived from the oxygen-restricted pyrolysis of biomass and is characterized as being biologically stable and having high porosity. Adding biochar to soil is a widely recognized strategy to increase soil carbon (C) stocks and improve soil chemical, physical, and biological properties. Accurate quantification of stable fractions of biochar from soil is vital to assessing its long-term C storage potential for accounting purposes. However, methods specifically developed for quantifying biochar in soils are limited with most current methods adapted from techniques for measuring black carbon (BC). This results in numerous drawbacks for the quantification of biochar. Drawing on existing techniques for determining BC, the potential biochar quantification methods are identified and ordered into four categories: thermal oxidation methods, chemical oxidation methods, benzene poly-carboxylic acids (BPCAs) molecular marker methods, and optical methods. Within this framework, this review then considers factors that might skew measurements, such as loss of biochar and interferences. Measurement principles, technical characteristics, and advantages and disadvantages associated with each of the methodologies are also examined. Ultimately, our objective is to provide researchers with a comprehensive understanding, enabling them to select the most appropriate biochar quantification methods.

Biochar aided with machine learning (ML) has been considered as a promising solution for addressing heavy metal (HM) pollution. While representing an emerging approach, the integration of ML with biochar is currently hindered by a lack of interpretability. In this study, eXtreme Gradient Boosting (XGBoost) demonstrated superior performance compared to the other four models, closely followed by Random Forest (RF). By incorporating interpretative tools such as Shapley Additive Explanations (SHAP) values, partial dependence plots (PDP), and feature importance analysis, we aimed to shed light on the black-box effect inherent in machine learning algorithms. The research findings highlight the optimal conditions for biochar adsorption, emphasizing the importance of specific surface area (SSA), solution pH, and adsorption time. Further investigation reveals that the biochar attains its optimal SSA at a pyrolysis temperature of approximately 600 degrees C, with an oxygen content of around 30 % and a nitrogen content of about 0.5 %, which corresponds to the best HM adsorption performance. The data adopted from a broad distribution range enhanced the generalization capability of ML models, reduced the risk of overfitting, and strengthened the model's robustness and fairness. By utilizing interpretable ML methods, this study provides a new insight into the synthesis of biochar and its role in HM adsorption, elucidating crucial factors and adsorption mechanisms with significant environmental and scientific implications.

Globally, soil contamination with arsenic (As) and lead (Pb) has become a severe environmental issue. Herein, a pot experiment was conducted using pak choi (Brassica chinensis L.) to investigate the effects of biochars derived from crawfish (Procambarus clarkia) shells (CSB) and Chinese banyan (Ficus microcarpa) branches (CBB) on the phytoavailability of As and Pb, and bacterial community composition in soils. Our results showed that the application of CSB and CBB decreased the concentrations of DTPA-extractable Pb in soils ranging from 26.8 % to 28.8 %, whereas CSB increased the concentration of NH4H2PO4-extractable As in soils, compared to the control. Application of both biochars reduced the uptake of As and Pb in the edible part of pak choi. In addition, application of CBB significantly (P < 0.05) increased the activities of α-glucosidase, β-glucosidase, cellobiohydrolase, and acid phosphomonoesterase by 55.0 %, 54.4 %, 195.1 %, and 76.7 %, respectively, compared to the control. High-throughput sequencing analysis revealed that the predominant bacteria at the phyla level in both biochar-treated soils were Firmicutes, Proteobacteria, and Actinobacteriota. Redundancy and correlation analyses showed that the changes in bacterial community composition could be related to soil organic carbon content, As availability, and nutrient availability in soils. Overall, the Chinese banyan branch biochar was more suitable than the crawfish shell biochar as a potential amendment for the remediation of soils co-contaminated with As and Pb.

Biochar has been widely used for in situ remediation of sediments in recent years because of its advantages including suitable surface area, pore structure, and abundant surface oxygen-containing functional groups. Nevertheless, leaching of some hazardous components of biochar, e.g., potentially toxic elements (PTEs), polycyclic aromatic hydrocarbons, persistent free radicals, dioxins-like compounds, etc., can pose ecological risks to the water–sediment system. In this review, the applications and associated mechanisms of biochar in the remediation of PTEs- and organic pollutants contaminated sediment systems have been illustrated and critically discussed. Additionally, the potentially hazardous constituents in biochar were summarized and the effects of biomass and production conditions on their bioavailability were reviewed. Furthermore, the effects of biochar addition on water/sediment eutrophication, phytotoxicity, benthic damage, and microbial community changes were discussed. On this basis, the monitoring and assessment measures of the potential risks of biochar were summarized, and the corresponding avoidance strategies for different risks were proposed. This paper aims to provide a baseline reference and guidance implications for the biochar selection, toxicity detection, and evaluation in the field of sediment remediation.

For agricultural systems, nitrogen (N) is an extremely important nutrient and is the most significant nutrient-limiting factor for productivity and constraining economic sustainability. Biochar-based N fertilizers (BBNFs) normally use a biochar/polymer coating of a synthetic fertilizer granule or through utilizing the structure of biochar for preparation. Biochar coating of mineral fertilizers is an entirely promising approach in the development of controlled-release fertilizers, providing a barrier to the dissolution and transport of nutrients thus limiting N loss pathways and mitigating environmental problems. Pseudo-first-order and pseudo-second-order kinetic models were used to investigate the cumulative N release from BBNFs. In recent years, there has been a growing focus on the impact of BBNFs on N cycling, with implications for both agronomic and environmental effects. While there is good evidence that BBNFs can improve N use efficiency, more research is needed to determine their ideal application rates and how these affect their economic feasibility when compared to traditional fertilizers.

Sorption and oxidation are two potential pathways for the decontamination of trivalent antimony (Sb(III))-bearing water, using iron (Fe)-modified biochar (FeBC). Here we investigated the sorption and oxidation behavior of FeBC for Sb(III) in aqueous solutions. Results revealed that Sb(III) removal by FeBC was significantly improved showing the maximum Sb(III) sorption (64.0 mg g-1). Density functional theory (DFT) calculations indicated that magnetite (Fe3O4) in FeBC offered a sorption energy of-0.22 eV, which is 5 times that of non-modified biochar. With the addition of peroxymonosulfate (PMS), the sorption of Sb(III) on FeBC was 7 times higher than that on BC, indicating the sorption capacity of FeBC for Sb(III) could be substantially increased by adding oxidizing agents. Electrochemical analysis showed that Fe modification imparted FeBC higher electron-donating capacity than that of BC (0.045 v. s. 0.023 mmol e- (g biochar)-1), which might be the reason for the strong Sb(III) oxidation (63.6%) on the surface of FeBC. This study provides new information that is key for the development of effective biochar-based composite materials for the removal of Sb(III) from drinking water and wastewater. The findings from this study have important implications for protecting human health and agriculture.

The combined effects of graphene and biochar for enhanced adsorption of organic pollutants have not been demonstrated yet. Therefore, the mechanisms of graphene-modified biochar synthesis and its application to adsorption of contaminants remain unclear. In this study, the effect of flake-size graphene on biochar modification and its bisphenol S (BPS) adsorption performance was explored for the first time. Three sizes of graphene oxide were used as the precursor to prepare graphene/biochar composites using pyrolysis. It was found that the graphene with a small flake size was interspersed in the macropores of biochar, while the biochar was completely or mostly wrapped by the large-sized graphene sheet, which effectively prevented the agglomeration and pore blockage of biochar. Large-flake graphene oxide modified biochar (LGB) showed the highest adsorption capacity towards BPS, exhibiting 2.8 times higher adsorption than pristine biochar. Density functional theory (DFT) calculation suggested that the maximum diffusion barrier of O atoms in graphene coated cellulose (most frequently used biochar representative) could be reduced significantly (∼46%) at pyrolysis temperature of 873 K. Taking the advantage of small amount of graphene and enhanced adsorption performance, LGB could be a promising adsorbent for the removal of certain organic pollutants from wastewater and is conducive for the development of high-valued biochar modification.

Sustainable management of ever-increasing organic biowaste and arable soil contamination by potentially toxic elements are of concern from both environmental and agricultural perspectives. To tackle the waste issue of crawfish shells and simultaneously minimize the threat of arsenic (As) and lead (Pb) to human health, a pot trial was conducted using chitin (CT), crawfish shell biochar (CSB), crawfish shell powder (CSP), and CT-CSB com-posite to compare their remediation efficiencies in As/Pb co-contaminated soil. Results demonstrated that addition of all amendments decreased Pb bioavailability, with the greatest effect observed for the CT-CSB treatment. Application of CSP and CSB increased the soil available As concentration, while significant decreases were observed in the CT and CT-CSB treatments. Meanwhile, CT addition was the most effective in enhancing the soil enzyme activities including acid phosphatase, alpha-glucosidase, N-acetyl-beta-glucosaminidase, and cellobio-hydrolase, whereas CSB-containing treatments suppressed the activities of most enzymes. The amendments altered the bacterial abundance and composition in soil. For instance, compared to the control, all treatments increased Chitinophagaceae abundance by 2.6-4.7%. The relative abundance of Comamonadaceae decreased by 1.6% in the CSB treatment, while 2.1% increase of Comamonadaceae was noted in the CT-CSB treatment. Redundancy and correlation analyses (at the family level) indicated that the changes in bacterial community structure were linked to bulk density, water content, and As/Pb availability of soils. Partial least squares path modeling further indicated that soil chemical property (i.e., pH, dissolved organic carbon, and cation exchange capacity) was the strongest predictor of As/Pb availability in soils following amendment application. Overall, CT-CSB could be a potentially effective amendment for simultaneously immobilizing As and Pb and restoring soil ecological functions in contaminated arable soils.

Contamination of aquatic and soil systems by organic and inorganic pollutants has become a serious issue of concern worldwide. Viable and cost-effective solutions are urgently needed to mitigate the negative impacts of diverse pollutants on the environment and human health. Biochar has emerged as an effective and green material for the remediation of a wide spectrum of (in)organic pollutants. However, applications of pristine biochar in decontamination have encountered bottlenecks due to its limited properties which cannot meet the desired remediation requirements. Therefore, multiple modification methods have been developed for tailoring the physicochemical properties of biochar to enhance its effectiveness in environmental decontamination. This work provides a holistic review on the recent advances on the synthesis of engineered biochar using physical, chemical, and biological methods. Further applications and related mechanisms of engineered biochar in the field of environmental decontamination in aquatic and soil systems have also been summarized and discussed. In addition, existing challenges and research gaps are outlined, and future research needs are proposed. This review summarizes the scientific opportunities for a comprehensive understanding of using engineered biochars as effective materials for the remediation of contaminated water and soil. Graphical abstract

Soil lead (Pb) contamination is often caused by anthropogenic activities. In this study, a pot experiment was conducted to assess the effect of biochars derived from pig-carcass (PCBC) and branches of oriental-plane tree (OPBC) on the bioavailability, redistribution, and phytoavailability of Pb and P, as well as the growth of Ipomoea aquatica Forsk in a Pb-contaminated soil. Application of PCBC increased the total and available P concentrations in the soil as compared to the control, and enhanced the concentrations of labile P and sparingly labile P via direct exogenous P input and improvement of soil pH. Both biochars facilitated P accumulation in plant shoots and roots. Sequential extraction of soil Pb confirmed that biochar application facilitated the transformation of mobile Pb into stable fractions, with greater effects from PCBC than OPBC. Hence, biochar application significantly decreased the soil DTPA-extractable Pb by 90.2% (PCBC) and 64.0% (OPBC) compared to the control, consequently reducing Pb uptake by plants. The Pb immobilization by biochar was driven by the biochar-induced increase of soil pH, Pb-phosphate/carbonate precipitation, ion exchange between Pb2+ and biochar-derived cations (e.g., Ca2+ and K+), and surface complexation with functional groups (e.g., carboxyl, hydroxyl, CO). Application of PCBC simultaneously increased the biomass of plant roots and shoots, by 1.8- and 0.6- folds, respectively. Overall, PCBC showed a potential to function as an effective amendment in the immobilization of Pb and alternative P fertilizer to improve degraded soils.

为探讨原始和铁改性生物质炭对污染土壤中砷(As)和铅(Pb)生物有效性和土壤微生物群落结构的影响,利用As-Pb复合污染水稻土进行水稻盆栽试验,分别在土壤中施加3％(质量分数)的原始法国梧桐枝条炭(法桐炭)、铁改性法国梧桐枝条炭(Fe-法桐炭)、原始猪炭(猪炭)、铁改性猪炭(Fe-猪炭).试验结束后测定土壤pH、有机碳等理化性质、土壤养分有效性、土壤有效态As和Pb、稻谷中As和Pb的含量及土壤微生物群落结构等指标.结果表明,与对照相比,施用Fe-法桐炭对土壤中As的钝化效果较好,降幅为39％;施用猪炭对土壤中Pb的钝化效果较好,降幅为19％;Fe-法桐炭的施用使稻谷中As含量降低了 80％.施用两种原始生物质炭后,土壤中的微生物群落多样性指数(Chao1、Shannon)和OTUs总数均显著)增加(p＜0.05),但相较于原始生物质炭,施用铁改性生物质炭均提高了土壤中优势菌群的相对丰度,且两种铁改性生物质炭处理土壤中的优势菌属为Actinobacteria_unclassified、Gaiellales_unclassified和Nocardioides.冗余分析表明,土壤中微生物群落组成与土壤pH和有效态As关系密切.因此,施用生物质炭可以通过改变土壤pH和降低As胁迫等性质影响土壤微生物群落结构.综上所述,经过铁改性处理的法桐炭更适用于As污染土壤修复,而原始猪炭是一种比较理想的Pb污染土壤修复材料.

Sorption and oxidation are two key pathways for the decontamination of antimonite (Sb(III))-bearing water using iron (Fe)-enabled biochars (FeBCs). We investigated sorption and oxidation behavior of FeBCs for Sb(III) in aqueous solutions. Results revealed that Sb(III) removal by FeBCs was significantly improved, with FeBC prepared at 500°C (FeBC500) showing the maximum Sb(III) sorption (64 mg g-1). Density functional theory (DFT) calculations indicated that the magnetite (Fe3O4) in FeBC500 offered a sorption energy of -0.22 eV, being 5-time as that on non-modified case. With the addition of peroxymonosulfate (PMS), the sorption of Sb(III) on FeBC500 was 7-time higher than that on BC500. Electron transfer experiments showed FeBC500 had higher electron acceptor capacity (0.045 mmol e- (g biochar)-1), which promoted the efficient oxidation of Sb(III) (63.6%). This study provides new information which is key for the development of an effective biochar-based composite materials for the removal of Sb(III) from water and wastewater.

Contamination of aquatic systems by antimony (Sb) is a worldwide issue due to its risks to eco-environment and human health. Batch sorption experiments were conducted to assess the equilibrium, kinetics and thermodynamics of antimonite [Sb(III)] sorption by pristine biochar (BC) and chitosan-loaded biochar (CHBC) derived from branches of Ficus microcarpa. Results showed the successful loading of chitosan onto biochar surface, exhibiting more functional groups (e.g., C--O, -NH2, and -OH). Langmuir model well described the Sb(III) sorption isotherm experimental data, and the maximum sorption capacity of Sb(III) by CH1BC (biochar loaded with chitosan at a ratio of 1:1) was 168 mg g-1, whereas for the BC it was only 10 mg g-1. X-ray photoelectron spectroscopy demonstrated that CH1BC oxidized 86% of Sb(III) to Sb(V), while BC oxidized 71% of Sb(III). Density functional theory calculations suggested that the synergistic effect of exogenous hydroxyl and inherent carbonyl contributed to the enhanced removal efficiency of Sb(III) by CHBC. Key mechanisms for Sb(III) sorption onto CHBCs included electrostatic interaction, chelation, surface complexation, 7C-7C interaction, and hydrogen bonding. Overall, this study implies that CHBC can be a new, viable sorbent for the removal of Sb(III) from aquatic systems aiding their safe and sustainable management.

Removal of antimonite [Sb(III)] from the aquatic environment and reducing its biotoxicity is urgently needed to safeguard environmental and human health. Herein, crawfish shell-derived biochars (CSB), pyrolyzed at 350, 500, and 650 ° C, were used to remediate Sb(III) in aqueous solutions. The adsorption data best fitted to the pseudo-second-order kinetic and Langmuir isotherm models. Biochar produced at 350 ° C (CSB350) showed the highest adsorption capacity (27.7 mg g − 1 ), and the maximum 78% oxidative conversion of Sb(III) to Sb(V). The adsorption results complemented with infrared (FTIR), X-ray photoelectron (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy analyses indicated that the adsorption of Sb(III) on CSB involved electrostatic interaction, surface complexation with oxygen-containing functional groups (C = O, O = C–O), π–π coordination with aromatic C = C and C–H groups, and H-bonding with –OH group. Density functional theory calculations verified that surface complexation was the most dominant adsorption mechanism, whilst π–π coordination and H-bonding played a secondary role. Furthermore, electron spin resonance (ESR) and mediated electrochemical reduction/oxidation (MER/MEO) analyses confirmed that Sb(III) oxidation at the biochar surface was governed by persistent free radicals (PFRs) (•O 2 − and •OH) and the electron donating/accepting capacity (EDC/EAC) of biochar. The abundance of preferable surface functional groups, high concentration of PFRs, and high EDC conferred CSB350 the property of an optimal adsorbent/oxidant for Sb(III) removal from water. The encouraging results of this study call for future trials to apply suitable biochar for removing Sb(III) from wastewater at pilot scale and optimize the process. Graphical abstract

为比较不同小龙虾壳基土壤改良剂对砷、铅复合污染土壤的修复效果,通过盆栽试验,探究施用1％(w/w)小龙虾壳粉(CSP)、甲壳素(CT)、小龙虾壳炭(CSB)及甲壳素-小龙虾壳炭配施(CT-CSB,CT∶CSB为1∶1)对土壤养分、酶活性、重金属生物有效性及青菜生长的影响.结果 表明,不同改良剂施用均可显著提高土壤pH和阳离子交换量,降低土壤中有效态铅的含量,施用CSB对降低土壤中有效态铅含量的效果最显著,较对照降低了35.3％;添加CT、CSB和CT-CSB均可降低土壤中有效态砷的含量,其中,CT-CSB处理较对照降低77.2％.CT、CSB、CT--CSB处理显著提高土壤中a-葡萄糖苷酶、纤维二糖水解酶、β-木糖苷酶、β-N-乙酰基氨基葡萄糖苷酶和酸性磷酸酶的活性.土壤酶活性与重金属有效态含量的相关性分析表明,施加改良剂可降低重金属胁迫,提高土壤酶活性.添加不同土壤改良剂均可降低青菜可食部分对砷和铅的积累,提高青菜对氮、磷和钾的吸收量,从而促进植物生长,CT-CSB处理的青菜可食部分生物量较对照提高190.9％.综上,CT、CSB、CT-CSB在砷铅复合污染土壤修复方面均有较大应用潜力,CSB综合效果最为明显,可以作为土壤砷、铅原位钝化修复的一种新材料.