Search

The combination of micron zero-valent iron (mZVI) and microorganisms is an effective method for trichloroethylene (TCE) degradation, but electron transfer efficiency needs improvement. A new chem-bio hybrid process using a composite material (S-ZVI@biochar) was developed, consisting of sulfurized mZVI and biochar as a chemical remover, and Shewanella oneidensis MR-1 and dechlorinating bacteria (DB) as a biological agent for TCE degradation. S-ZVI@biochar showed improved stability, biocompatibility, and TCE removal compared to ZVI and S-ZVI. The hybrid system DB + MR-1 + S-ZVI@biochar exhibited the highest TCE removal efficiency at 96.5% after 30 days, which was 3.7 times higher than that of bare ZVI. The study revealed that the enhanced dechlorination performance was due to improved electron transfer efficiency, adjustment of microbial community structure, and iron recycling. S-ZVI@biochar constructed electron transport channels in the composite system, improving the overall dechlorination capacity. This system shows promise for long-term TCE removal in anaerobic environments. [ABSTRACT FROM AUTHOR]

Biochar application to the soil is a novel approach to carbon sequestration. Biochar application affects the emission of greenhouse gases (GHGs), such as CO2, CH4, and N2O, from different environments (e.g., upland soils, rice paddies and wetlands, and composting environments). In this review, the effect of biochar on GHGs emissions from the above three typical environments are critically evaluated based on a literature analysis. First, the properties of biochar and engineered biochar related to GHGs emissions was reviewed, targeting its relationship with climate change mitigation. Then, a meta‐analysis was conducted to assess the effect of biochar on the emissions of CO2, CH4, and N2O in different environments, and the relevant mechanisms. Several parameters were identified as the main influencing factors in the meta‐analysis, including the pH of the biochar, feedstock type, pyrolysis temperature, biochar application rate, C/N ratio of the biochar, and experimental scale. An overall suppression effect among different environments was found, in the following order for different greenhouse gases: N2O > CH4 > CO2. We conclude that biochar can change the physicochemical properties of soil and compost in different environments, which further shapes the microbial community in a specific environment. Biochar addition affects CO2 emissions by influencing oligotrophic and copiotrophic bacteria; CH4 emissions by regulating the abundance of functional genes, such as mcrA (a methanogen) and pmoA (a methanotroph); and N2O emissions by controlling N‐cycling functional genes, including amoA, nirS, nirK, nosZ. Finally, future research directions for mitigating greenhouse gas emissions through biochar application are suggested. [ABSTRACT FROM AUTHOR]

Single-atom catalyst has shown promising effect in photocatalysis. In particular, the construction of bimetallic catalytic sites can address the limitations of single-metallic catalysts, such as clustering and slow electron transfer, which enhances electron transfer between active sites and promotes photocatalytic activity. In this paper, Mn and Co bimetallic catalyst (Mn/Co@N-biochar) was developed by using the electronegativity difference of the bimetallic sites on N-doped biochar to construct catalytically active sites to enhance electron transfer. XRD and HR-TEM characterization confirmed that metal atoms were evenly dispersed within the carbon layer without aggregation or clustering of metal particles. The catalytic efficiency of Mn/Co@N-biochar was assessed through sulfanilamide (SNM) degradation experiments, demonstrating a remarkable degradation rate of 99.3% and a mineralization rate of 49.0%. These values were 10.45 times and 13.24 times more than that for biochar, respectively, indicating that the loading of bimetals greatly improved the photocatalytic activity. Furthermore, the doping of N atoms adjusted the electronic structure of adjacent C atoms and activated the free-flowing π electrons on the biochar surface, creating solid anchoring sites that facilitated efficient electron circulation between Mn and Co atomic sites. The higher local electron density at the Co-N 4 site compared to the Mn-N 4 , created electron transfer channels, where Mn atoms (catalytic site) facilitated the flow of electrons to Co atoms (active site). This could rapidly generate the primary active species (‧OH and ‧O 2 -) to degrade SNM. Additionally, the stability and applicability of bimetallic catalysts in real water systems were also confirmed, providing valuable insights for the construction of bimetallic biochar structures to degrade organic pollutants in water. [Display omitted] • A bimetal-loaded N-doped biochar photocatalyst was designed for degradation of SNM. • In N-doped biochar, Mn/Co sites show high dispersion and stability. • Electron channels were formed for Mn (driving sites) to drive Co (reaction sites). • Mn/Co@N-biochar demonstrated stability and applicability in real water systems. • Mn/Co sites promoted electron-hole separation, and enhanced the use of ‧OH and ‧O 2 -. [ABSTRACT FROM AUTHOR]

In order to enhance the removal performance of graphitic carbon nitride (g-C 3 N 4) on organic pollutant, a simultaneous process of adsorption and photocatalysis was achieved via the compounding of biochar and g-C 3 N 4. In this study, g-C 3 N 4 was obtained by a condensation reaction of melamine at 550°C. Then the g-C 3 N 4 /biochar composites were synthesized by ball milling biochar and g-C 3 N 4 together, which was considered as a simple, economical, and green strategy. The characterization of resulting g-C 3 N 4 /biochar suggested that biochar and g-C 3 N 4 achieved effective linkage. The adsorption and photocatalytic performance of the composites were evaluated with enrofloxacin (EFA) as a model pollutant. The result showed that all the g-C 3 N 4 /biochar composites displayed higher adsorption and photocatalytic performance to EFA than that of pure g-C 3 N 4. The 50% g-C 3 N 4 /biochar performed best and removed 45.2% and 81.1% of EFA (10 mg/L) under darkness and light with a dosage of 1 mg/mL, while g-C 3 N 4 were 19.0% and 27.3%, respectively. Besides, 50% g-C 3 N 4 /biochar showed the highest total organic carbon (TOC) removal efficiency (65.9%). Radical trapping experiments suggested that superoxide radical (•O 2 −) and hole (h+) were the main active species in the photocatalytic process. After 4 cycles, the composite still exhibited activity for catalytic removal of EFA. [Display omitted] [ABSTRACT FROM AUTHOR]

Much effort has been made to use biochar to catalyze organic solid waste conversion into value-added products. Biochar has a high specific surface area and abundant functional groups, making it a promising catalyst, but biochar is not used in industrial-scale applications. Presented here is a systematic literature review and bibliometric analysis of biochar-catalyzed solid waste research between 2000 and 2023 focused on the mechanisms involved in and factors affecting biochar catalytic performance during biomass and organic polymer conversion. In situ catalysis allows flexible and simple processes giving specific products but gives relatively poor conversion efficiencies. Catalytic conversion of organic solid waste by biochar has been a focus of research since 2006. A discussion of biochar catalysis applications, computational approaches, and sustainability is presented. The review indicates recent progress using biochars as catalysts for converting waste into valuable products and provides valuable insights that will advance environmental and waste management practices. [Display omitted] • A systematic literature review and bibliometric analysis of biochar-catalyzed waste was conducted. • Ex-situ catalysis has better product selectivity but lower conversion efficiency. • Conversion of wastes into functional materials has become a research hotspot since 2006. • Biochar has significant potential in the catalytic conversion of polymers and biomass. • Delve into biochar's integration with computation, applications, & sustainability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reduction of Cr(VI) occurs mainly on solid surfaces of the multiple interfaces from ternary composites. • Micron zero-valent iron powder activated by low-cost natural pyrite and biochar provide a long-lasting reduction for Cr(VI). • Biochar acts as a conductor, adsorber, and disperser in the reaction system. • The electron selectivity and utilization rate of the composite toward Cr(VI) were 14.20% and 48.08%, respectively. • 70.07% of Cr(VI) removal was due to reduction/precipitation and 29.93% was ascribed to surface sorption. Current studies have confirmed that sulfidation is an effective method to enhance the reduction capacity of zero-valent iron (ZVI), however, the cost of sulfidation and the durability of the material are still the challenges of material reducibility. In this work, ternary composites of natural pyrite (FeS 2), zero-valent iron powder, and pine wood biochar (BC) were synthesized by simple ball milling technology (BM) and applied for the removal of hexavalent chromium (Cr(VI)) in aqueous solution. Batch sorption experiments of each component and composites at various mass rates conformed that the adsorption capacity of BMFeS 2 /ZVI/BC at 1:1:1 (81.5 mg·g−1) exceeded two to three-fold of Cr (VI) than their individuals. Comparative experiments on two groups with various raw material ratios indicated the balance between biochar-related adsorption capacity and reduction-related S/Fe was imperative. The analysis and calculation of the products yielded 70.07 % of Cr(VI) removal due to reduction/precipitation and 29.93 % was ascribed to surface sorption at the equilibrium Cr(VI) concentration of 33.76 mg·L−1. The electron selectivity (ES) and utilization rate (UR) of 1:1:1 toward Cr(VI) were determined to be 14.20 % and 48.08 %, respectively. A negligible metal ion leakage was observed upon pH > 5.5. Shielding experiments of Fe2+, TEM, and XPS analysis proved the reduction of Cr(VI) occurred mainly on solid surfaces. The role of biochar in the reaction system was identified as conductor, adsorber, and disperser. The multiple interfaces caused by ball milling provide different reduction pathways. Nevertheless, reduction, adsorption, and surface complexation were the dominant mechanisms for Cr(VI) removal. This work demonstrates the potential of natural pyrite for the preparation of BMFeS 2 /ZVI/BC composite to remove Cr(VI) from water and wastewater. [ABSTRACT FROM AUTHOR]

Ball-milled biochars (BM-biochars) were produced through ball milling of pristine biochars derived from different biomass at three pyrolysis temperatures (300, 450, and 600 °C). The results of scanning electron microscopic (SEM), surface area, hydrodynamic diameter test, and Fourier transform infrared spectroscopy (FTIR) revealed that BM-biochars had smaller particle size (140–250 nm compared to 0.5–1 mm for unmilled biochar), greater stability, and more oxygen-containing functional groups (2.2–4.4 mmol/g compared to 0.8–2.9 for unmilled biochar) than the pristine biochars. With these changes, all the BM-biochar-modified glassy carbon electrodes (BM-biochar/GCEs) exhibited prominent electrochemical properties (e.g., ΔEp of 119–254 mV compared to 850 mV for bare GCE). Cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) show that ball-milled 600 °C biochar/GCE (BMBB600/GCE and BMBG600/GCE) had the smallest peak-to-peak separation (ΔEp = 119 and 132 mV, respectively), series resistance (RS = 88.7 and 89.5 Ω, respectively), and charge transfer resistance (RCT = 1224 and 1382 Ω, respectively), implying its best electrocatalytic activity for the reduction of Fe(CN)63−. It is supposed that the special structure (i.e., internal surface area, pore volume, oxygen-containing functional groups, and graphitic structure) facilitates the electron transfer and reduces interface resistance. Economic cost of BM-biochar/GCE was 1.97 × 10−7 USD/cm2, much lower than that of a "low-cost platinum electrode" (0.03 USD/cm2). The results indicate potential application of the novel BM-biochar for low cost and high efficient electrodes. [ABSTRACT FROM AUTHOR]

Abstract In this study, novel biochar supported nano-scale zero-valent iron (biochar-CMC-nZVI) stabilized by carboxymethyl cellulose (CMC) was developed and used for the removal of hexavalent chromium (Cr(VI) from aqueous solution. With the stabilization of CMC, nZVI particles (about 80 nm) were effectively dispersed onto the surface of biochar, which inhibited the aggregation of nZVI and resulted in the smaller particle size of nZVI on the surface of biochar. The results showed that the specific surface area of the composite was 11.1 m2/g, lower than that of pristine biochar. The basic element composition was C, O, and Fe with a large number of oxygen-containing functional groups (−COOH, OH, and O C O) observed on the surface. Cr(VI) was reduced to Cr(III) by the composite material, mainly due to the reduction of nZVI on the biochar surface. Upon reaction with Cr(VI), Cr x Fe 1-x (OH) 3 and Fe x Cr y O 4 were deposited on the surface of biochar-CMC-nZVI composite. Electrostatic attraction, reduction, and surface complexation were the dominant removal mechanisms. The results showed that the 100 mg/L Cr(VI) could be removed completely by biochar-CMC-nZVI within 18 h, at a dosage of 1.25 g/L and an initial pH of 5.6. Cr(VI) removal by biochar-CMC-nZVI was favored by lower pH. The pseudo-second-order kinetic model and the Langmuir isothermal adsorption model fitted well with the sorption kinetic and isotherm data, indicated Cr(VI) adsorption mechanism was a chemisorption based multi-layer adsorption. The present study demonstrated the promise of biochar-CMC-nZVI composite as a low-cost, "green", and effective sorbent for removal of Cr(VI) in the environment. Graphical abstract Image 1 Highlights • CMC supported the development of spherical nZVI on biochar. • Biochar-CMC-nZVI composite showed enhanced removal ability of Cr(VI). • pH has important effect on the reaction process. • The mechanism of the Cr(VI) removal was mainly chemical reduction. [ABSTRACT FROM AUTHOR]

Abstract A sequential chem-bio hybrid process was developed using a novel biochar supported carboxymethyl cellulose-stabilized nanoscale iron sulfide (CMC-FeS@biochar) as a chemical remover and Corynebacterium variabile HRJ4 as a biological agent for trichloroethylene (TCE) degradation. Compared with CMC-FeS, FeS@biochar600, bare FeS and biochar600, the CMC-FeS@biochar600 composite displayed better physiochemical properties (smaller hydrodynamic diameter and higher stability) and demonstrated excellent removal capacity for TCE from aqueous phase. A facultative bacterial strain, Corynebacterium variabile HRJ4, growing well in the presence of CMC-FeS@biochar (added up to 0.25 g L−1), further enhanced TCE removal after chemical treatment. The dechlorination pathway proposed based on the gas chromatography–mass spectrometry (GC-MS) analysis revealed that TCE was dechlorinated to cis -1,2-dichloroethene (cis -DCE) and acetylene via hydrogenolysis and β -elimination, respectively within 12 h by CMC-FeS@biochar. Addition of HRJ4 strain into the reaction system effectively enhanced the degradation of the residual TCE, cis -DCE and acetylene to ethylene. Acetylene was the main product in chemical process, whereas ethylene was the main product in biological process as strain HRJ4 could reduce acetylene to ethylene effectively. The results of this study signify the potential application of CMC-FeS@biochar600/HRJ4 chem-bio hybrid system for complete degradation of TCE in the anaerobic environment. Graphical abstract Image 1 Highlights • CMC-FeS@biochar was synthesized combining the advantages of biochar, CMC, and FeS. • CMC-FeS@biochar had higher TCE removal ability. • Corynebacterium variabile HRJ4 displayed potential for TCE transformation. • Chem-bio hybrid process can completely dechlorinate TCE to ethylene. [ABSTRACT FROM AUTHOR]

Novel adsorbents were produced through the grinding of biochars of different feedstock and pyrolysis temperature in a planetary ball mill. The removal effectiveness and mechanisms of aqueous methylene blue by these adsorbents were examined. Ball milled sugarcane bagasse biomass pyrolyzed at 450 °C (BMBG450) had the highest methylene blue sorption capacity thus was chosen for further study. Compared to unmilled bagasse biochar (BG450), BMBG450 had greater specific surface area, larger pore volume, smaller hydrodynamic radius, stronger negative zeta potential (about 1.6-fold increase), and more oxygen-containing functional groups (1.05 mmol/g increase). These characteristics resulted in much greater methylene blue removal capacity (354 mg/g Langmuir maximum adsorption capacity vs. 17.2 mg/g of original BG450). The increased in BM–biochar’s external and internal surface areas exposed its graphitic structure and oxygen-containing functional groups, thus enhancing methylene blue adsorption via π–π interaction and electrostatic attraction. Experimental and modeling results suggest external mass transfer as the rate-limiting adsorption step for BG450 and surface diffusion as the rate-limiting adsorption step for BMBG450. BM–biochars had a lower equilibrium dosage and shorter reactor detention time when applied in a completely mixed flow reactor (CMFR). [ABSTRACT FROM AUTHOR]

Biochar supported carboxymethyl cellulose (CMC)-stabilized nanoscale iron sulfide (FeS) composite (CMC-FeS@biochar) was prepared and tested for immobilization of hexavalent chromium Cr(VI) in soil. Results of UV–vis and transmission electron microscopy (TEM) showed that the backbone of biochar suppressed the aggregation of FeS, resulting in smaller particle size and more sorption sites than bare FeS. The composite at a dosage of 2.5 mg per gram soil displayed an enhanced Cr(VI) immobilization efficiency (a 94.7% reduction in the toxicity characteristic leaching procedure (TCLP) based leachability and a 95.6% reduction in the CaCl 2 extraction) compared to plain biochar and bare FeS. Sequential extraction procedure (SEP) and X-ray photoelectron spectroscopy (XPS) analysis suggested that CMC-FeS@biochar promoted the conversion of more accessible Cr (exchangeable and carbonate-bound fractions) into the less accessible forms (iron-manganese oxides-bound, organic material-bound, and residual fractions) to reduce the toxicity of Cr(VI) and that surface sorption and reduction were dominant mechanisms for Cr(VI) immobilization. CMC-FeS@biochar greatly reduced the bioavailability of Cr(VI) to wheat and earthworms ( Eisenia fetida ). Moreover, the application of CMC-FeS@biochar enhanced soil organic matter content and microbial activity. This work highlighted the potential of CMC-FeS@biochar composite as a low-cost, “green”, and effective amendment for immobilizing Cr(VI) in contaminated soils and improving soil properties. [ABSTRACT FROM AUTHOR]

With the goal of combining the advantages of ball-milling and biochar technologies, a variety of ball-milled biochars (BM-biochars) were synthesized, characterized, and tested for nickel (Ni(II)) removal from aqueous solution. Ball milling increased only the external surface area of low temperature biochars, but still dramatically enhanced their ability to sorb aqueous Ni(II). For higher temperature biochars with relatively low surface area, ball milling increased both external and internal surface area. Measurements of pH, zeta potential, stability, and Boehm titration demonstrated that ball milling also added oxygen-containing functional groups (e.g., carboxyl, lactonic, and hydroxyl) to biochar's surface. With these changed, all the BM-biochars showed much better Ni(II) removal efficiency than unmilled biochars. Ball-milled 600 °C bagasse biochar (BMBG600) showed the greatest Ni(II) adsorption capacity (230–650 compared to 26–110 mmol/kg for unmilled biochar) and the adsorption was dosage and pH dependent. Compared with the unmilled biochar, BMBG600 also displayed faster adsorption kinetics, likely due to an increase in rates of intra-particle diffusion in the latter. Experimental and modeling results suggest that the increase in BM-biochar's external and internal surface areas exposed its graphitic structure, thus enhancing Ni(II) adsorption via strong cation-π interaction. In addition, the increase in acidic surface functional groups enhanced Ni(II) adsorption by BM-biochar via electrostatic interaction and surface complexation. Ball milling thus has great potential to increase the efficiency of environmentally friendly biochar for various environmental applications. [ABSTRACT FROM AUTHOR]

A core-shell structure of sulfidated nanoscale zero-valent iron deposited on biochar (S-nZVI/BC) was synthesized and the performance of S-nZVI/BC on tetrabromobisphenol A (TBBPA) degradation was investigated. Detailed characterizations indicated that controlling S content altered distribution of S species (i.e., S2-, S 2 2-, and S n 2-) in shell and core and achieved higher hydrophobicity and lower electron-transfer resistance. S-nZVI/BC was highly reactive (∼4.3–11.3 times) and selective (∼78.9–152.6 times) over nZVI/BC for TBBPA degradation. Besides, BC improved reactivity and selectivity of S-nZVI by 0.17 and 1.35 times, respectively, deriving from increased electron-transfer, enhanced hydrophobicity, and more surface reduced S species. Thus, sulfidation and BC enhanced reactivity and selectivity of S-nZVI/BC by combining respective merits. Effects of initial TBBPA concentration, pH, and particles dosage on TBBPA degradation by S-nZVI/BC were also investigated. Remarkably, mechanism investigation revealed that core properties instead of shell dominated reactivity and TBBPA debromination mainly involved direct electron-transfer rather than atomic H. [Display omitted] • S-nZVI/BC exhibited high reactivity and selectivity on TBBPA degradation. • The BC improved electron-transfer and hydrophobicity of S-nZVI. • The core properties instead of shell was a determining factor for reactivity. • Direct electron transfer dominated debromination mechanism rather than atomic H. • The system combined advantages of sulfidation and BC for enhanced TBBPA reduction. [ABSTRACT FROM AUTHOR]

A novel biochar supported nanoscale iron sulfide (FeS) composite (CMC-FeS@biochar) combining the advantages of biochar, carboxymethyl cellulose (CMC), and FeS was synthesized and tested for Cr(VI) removal efficiency and mechanisms. FeS particles were effectively soldered onto the surface of biochar through OH, C C, O C O, C O, and Si O functional groups. The composite at a mass ratio of FeS:CMC: biochar = 1:1:1 displayed an enhanced Cr(VI) adsorption capacity of 130.5 mg/g at pH 5.5 compared to 38.6 mg/g for FeS and 25.4 mg/g for biochar. Surface sorption and reduction were the dominant removal mechanisms. At the equilibrium Cr(VI) concentration of 13.4 mg/L, 57% of Cr(VI) removal was attributed to reduction and 43% was ascribed to surface sorption. The adsorption kinetic data were adequately simulated with pseudo second-order kinetic model and mass transfer model, suggesting that sorption kinetics were the combination of chemisorption and external mass transfer. The Redlich-Peterson model fitted better than the Langmuir and Freundlich models in simulating the adsorption isotherm data, again suggesting a hybrid chemical reaction-sorption process. The Dubinin–Radushkevich isotherm model resulted in an adsorption energy of 10.0 kJ/mol, implying a chemisorption between Cr(VI) and CMC-FeS@biochar. The present study demonstrated the promise of CMC-FeS@biochar composite as a low-cost, “green”, and effective sorbent for removal of Cr(VI) in the environment. [ABSTRACT FROM AUTHOR]

Biochars have increasingly been used as adsorbents for organic and inorganic contaminants in soils. However, during the carbonization process of pyrolysis, contaminants, including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dioxins and furans (PCDD/DF) can be generated. In this study, biochars made from sawdust, were prepared at various temperatures ranging from 250 to 700 °C. The Microtox ® and rat hepatoma cell line H4IIE- luc assays were used to characterize the general toxic and effects, mediated through the aryl hydrocarbon receptor (AhR), or dioxin-like potencies of organic extracts of biochars. The greatest total concentrations of PAHs (8.6 × 10 2 μg kg −1 ) and PCDD/DF (6.1 × 10 2 pg g −1 ) were found in biochar generated at 400 °C and 300 °C, respectively. Results of the H4IIE- luc assay, which gives total concentrations of 2,3,7,8-TCDD equivalents (TEQ H4IIE- luc ), indicated that total potencies of aryl hydrocarbon receptor (AhR) agonists were in decreasing order: 300 °C > 250 °C > 400 °C > 500 °C > 700 °C. The 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQ chem ) calculated as the sum of products of 16 PAHs and 17 PCDD/DF congers multiplied by their respective relative potencies (RePs) was less than that of TEQ H4IIE- luc determined by use of the bioanalytical method, with the H4IIE- luc assay, which measures the total dioxin-like potency of a mixtures. The ratio of TEQ chem /TEQ H4IIE- luc was in the range of 0.7%–3.8%. Thus, a rather small proportion of the AhR-mediated potencies extracted from biochars were identified by instrumental analyses. Results of the Microtox test showed similar tendencies as those of the H4IIE- luc test, and a linear correlation between EC50 of Microtox test and EC20 of H4IIE- luc test was found. The results demonstrated that biochars produced at higher pyrolysis temperatures (>400 °C) were less toxic and had lower potencies of AhR-mediated effects, which may be more suitable for soil application. [ABSTRACT FROM AUTHOR]

Electroplating sludge (ES) containing large quantities of heavy metals is regarded as a hazardous waste in China. This paper introduced a simple method of treating ES using environmentally friendly fixatives biochar (BC) and iron sulfide (FeS), respectively. After 3 days of treatment with FeS at a FeS-to-ES mass ratio of 1:5, the toxicity characteristic leaching procedure (TCLP)-based leachability of total Cr (TCr), Cu(II), Ni(II), Pb(II), and Zn(II) was decreased by 59.6, 100, 63.8, 73.5, and 90.5 %, respectively. After 5 days of treatment with BC at a BC-to-ES mass ratio of 1:2, the TCLP-based leachability was declined by 35.1, 30.6, 22.3, 23.1, and 22.4 %, respectively. Pseudo first-order kinetic model adequately simulated the sorption kinetic data. Structure and morphology analysis showed that adsorption, electrostatic attraction, surface complexation, and chemical precipitation were dominant mechanisms for heavy metals immobilization by BC, and that chemical precipitation (formation of metal sulfide and hydroxide precipitates), iron exchange (formation of CuFeS), and surface complexation were mainly responsible for heavy metals removal by FeS. Economic costs of BC and FeS were 500 and 768 CNY/t, lower than that of NaS (940 CNY/t). The results suggest that BC and FeS are effective, economic, and environmentally friendly fixatives for immobilization of heavy metals in ES before landfill disposal. [ABSTRACT FROM AUTHOR]

A set of soil under the addition of ball-milled biochar (BM-biochar) from different feedstocks (wheat straw (WS) and rice husk (RH)) and pyrolysis temperature (300 °C, 500 °C, and 700 °C) was established to analyze the tetracycline (TC) degradation performance enhancement and greenhouse gas carbon dioxide (CO 2), and nitrous oxide (N 2 O) emission reduction from various angles, including physicochemical properties of soil and microbial community structure. After 45 days' incubation, the pH value decreased slightly from 7.34 to 7.22 for WS biochar-treated soil, while slightly increased from 7.34 to 7.50 for RH biochar-treated soil. The lowest KCl-leachable TC concentrations of BMWS700 and RH700 was about 0.0037 mg/L. Ball-milled 500 °C and 700 °C biochars enhanced the removal rate of TC significantly. The maximum reduction of TC was from 2.17 to 0.079 mg/kg, equivalent to 96% removal after ball-milled 500 °C wheat straw biochar (BMWS500) addition, suggesting the promoting effect of biochars on microorganisms for adsorption and degradation of TC. Biochars' addition reduced CO 2 and N 2 O emissions, BM-biochar enlarged this effect under the pyrolysis temperature 500 °C for both feedstock types. Ball milled rice husk biochar pyrolyzed under 500 °C (BMRH500) presented the maximum inhibitory effect CO 2 emission. The addition of BM-biochar changed the microbial community and diversity. The relative abundance of bacterium and fungus such as Proteobacteria , Acidobacteria , Chlorofexi , Mortierella , and Chaetomium increased due to BM-biochar addition, which promoted the degradation of TC and gave rise to more healthy soil environment for plant or microbes. The larger specific surface area, π–π interactions, hydrophobic interaction, and hydrogen bonding are account for better adsorption and degradation of TC by BM-biochars. This work elucidated the management of organic contaminants in real soil by BM-biochar. [Display omitted] • Ball-milled 500 °C biochar enhanced the tetracycline removal rate to 96%. • Sorption and degradation are dominant removal mechanisms. • Greenhouse gases emission was significantly suppressed after biochars' application. • The addition of ball-milled biochar reshaped the community structures of microbes. [ABSTRACT FROM AUTHOR]

Persulfate-based advanced oxidation process is considered as a promising technology for the degradation of phenol, where efficient, cost effective, and green methods with high peroxydisulfate (PS) activation capacity is of increasing demand. In this work, an in- situ liquid phase precipitation combined with ball milling method was applied for the synthesized of α- FeOOH/biochar, as be the PS activator for phenol degradation. Results showed that the ball-milled α- FeOOH and red pine wood biochar prepared at 700 °C (BM- α- FeOOH/PBC700) exhibited the highest catalytic property with PS for phenol oxidation (a phenol removal rate of 100%), compared with the BM- α- FeOOH (16.0%) and BMPBC700 (66.3%). The presence of intermediate products such as hydroquinone and catechol, and total organic carbon (TOC) removal rate (88.9%) proved the oxidation of phenol in the BM- α- FeOOH/PBC700+PS system. The characterization results showed that the functional groups (e.g., C O, C–O, Fe–O, and Si–O), the dissolved organic matter (DOM) in biochar, the loading of Fe element, and higher degree of graphitization and defect structures, contributed to the activation of PS to form free radicals (i.e., SO 4 · −, ·OH, ·O 2 −, and h VB +) for phenol oxidation, of which, SO 4 ·− and ·OH account for 72.1% of the phenol removal rate. The specific contribution to the PS activation for phenol oxidation by each part of the materials was calculated based on the "whole to part" experiment. The contribution of DOM, acid-soluble substance, and carbon matrix and basal part in BM- α -FeOOH/PBC700 were 6.0%, 40.9%, and 53.1%, respectively. The reusability experiments of BM- α -FeOOH/PBC700 demonstrated that the composite was relatively stable after four cycles of reuse. Among three co-existing anions (NO 3 −, Cl−, and HCO 3 −), HCO 3 − played the most significant inhibition effects on phenol removal through reducing the phenol removal rate from 89.6% to 77.9%. This work provides guidance for the design of high active and stable carbon materials that activate PS to remove phenol. [ABSTRACT FROM AUTHOR]

Biochar/iron (BC/Fe) composites, such as nano zero-valent iron (nZVI)/BC, iron sulfide/BC, and iron oxide/BC, have been developed and applied to deal with various contaminants owing to their excellent physicochemical properties. This work summarizes the progress in the preparation of BC/Fe composites, the properties and applications of BC/Fe, and the mechanism of the synergistic effect between Fe and BC in the composites. Various methods, including pyrolysis, hydrothermal carbonization, fractional precipitation, and ball milling, have been used to synthesize BC/Fe composites. In addition, the introduction of stabilizers, such as carboxymethyl cellulose (CMC), in the fractional precipitation process further prevents the agglomeration of Fe particles, which enhances the stability and fluidity of the resultant composites to facilitate the application of the composites in soil and water remediation. The application of BC/Fe composites in water and soil remediation is discussed in three aspects based on the interaction mechanisms, namely adsorption, reduction, and oxidation. Overall, the composites showed the synergistic effect of BC and Fe owing to the combination of the specific properties of Fe, such as reduction, catalysis, and magnetism, which can enhance the properties of BC with a larger surface area, abundant functional groups, and increased electron transfer efficiency. This review systemically summarizes the recent developments in BC/Fe composites to maximize the efficiency of BC/Fe application in soil and groundwater remediation. Key challenges and further research needs are also suggested. Image 100 • BC/Fe composites can be divided into three types based on their functions. • Synthesis methods play an important role in the combination of BC and Fe. • This review reveals the mechanism of the synergistic effect between Fe and BC. • This review maximizes the efficiency of BC/Fe application. [ABSTRACT FROM AUTHOR]

• Ball-milled biochar was first employed in the photocatalytic degradation of EFA. • Ball milling promoted the generation of ROS by biochars. • Ball-milled biochar dramatically increased the photocatalytic degradation of EFA. • A semiconductor-like structure of ball-milled biochar played a dominant role. • The possible degradation pathway of EFA by BM300 was proposed. Ball-milled biochar with enhanced physicochemical and sorption properties has been intensively investigated, but its photochemistry is far less studied. In this study, biochars produced at various pyrolysis temperatures were ball-milled and tested to determine enrofloxacin (EFA) photocatalytic degradation and its mechanisms. Ball-milled biochar could generate more O 2 − under visible light irradiation, which favored the photocatalytic degradation of EFA. The ball-milled biochar pyrolyzed at 300 °C (BM300) exhibited the highest EFA degradation rate (80.2% compared with 13.9% for unmilled biochar) and mineralization ability (66.4% compared with 0% for unmilled biochar). The characterization results suggested that more oxygen-containing functional groups played a significant role in the enhancement of photocatalytic performance. Based on the characterization and experiment results, it was supposed that a semiconductor-like structure played a main role in photocatalysis of BM300. A new mechanism suggested that the electrons in carbon defects (as valence band) could be excited by visible light and move to oxygen-containing functional groups (as conduction band), then the electrons in conduction band was further transferred to dissolved oxygen to produce O 2 −, and h + could be formed in valence band at the same time. This work applied ball-milled biochar to the field of photocatalysis for the first time, and provided a new opportunity for the removal of EFA in aqueous solutions. [ABSTRACT FROM AUTHOR]

• Thiol-modified biochar was synthesized by simply ball milling biochar with 3-MPTS. • BMS-biochar showed enhanced sorption for Hg2+ and CH 3 Hg+ compared to CIS-biochar. • Mercury was removed by electrostatic attraction, ligand exchange, and complexation. • Surface diffusion was the rate-limiting adsorption step for BMS-biochar. • Hg2+ and CH 3 Hg+ adsorption was a monolayer adsorption on heterogeneous surfaces. Modification of thiol on biochar often demands complex synthetic procedures and chemicals. In this work, a simple and environment friendly thiol-modified biochar (BMS-biochar) was successfully synthesized by ball milling pristine biochar with 3-mercaptopropyltrimethoxysilane (3-MPTS). The resultant BMS-biochar was characterized and tested for aqueous inorganic Hg2+ and organic CH 3 Hg+ removal. Characterization results showed that 3-MPTS was loaded on the surface of biochar through oxygen-containing functional groups (i.e., OH and C O) and π–π bond. Ball milling method improved the properties of BMS-biochar, namely, more efficient SH load, a larger surface area, more functional groups, more negatively charged surface, which resulted in higher removal efficiency of Hg2+ and CH 3 Hg+ (320.1 mg/g for Hg2+ and 104.9 mg/g for CH 3 Hg+) compared to the pristine biochar (105.7 mg/g for Hg2+ and 8.21 mg/g for CH 3 Hg+) and thiol-modified biochar through chemical impregnation (CIS-biochar) (175.6 mg/g for Hg2+ and 58.0 mg/g for CH 3 Hg+). Ball milling increased the sorption capacities of Hg2+ and CH 3 Hg+ through surface adsorption, electrostatic attraction, ligand exchange, and surface complexation. Modeling results suggested that the surface diffusion was the rate-limiting adsorption step for BMS-biochar. This work gave prominence to the potential of ball milling for the preparation of thiol-modified biochar to remove mercury especially organic CH 3 Hg+ by adsorption. [ABSTRACT FROM AUTHOR]

With a wide range of raw materials, low cost and large specific surface area, biochar has been widely used in environmental remediation. However, the biochar has a saturated adsorption capacity when it is used as a pollutant adsorbent. Recent efforts have been made to prepare biochar and biochar-based catalysts with enhanced catalytic properties to expand their potential applications. The environmental persistent free radicals (EPFRs) of biochar could react with O 2 to induce hydroxyl radicals (•OH) without the addition of oxidants. When oxidants were added, biochar and biochar-based catalysts could activate them to generate •OH and sulfate radicals (SO 4 •−), respectively. Moreover, biochar could act as an electron acceptor to improve the photodegradation capacity of catalysts. With reference to the information regarding biochar and biochar-based catalysts, this work provides a critical review on recent research development as follows: 1) the preparations of various types of biochar and biochar-based catalysts are summarized; 2) the effects of the synthetic conditions and transition metals on the catalytic activity of biochar-based catalysts are discussed; (3) methods for characterizing the active sites of the biochar-based catalysts are described; and (4) the environmental applications of biochar and biochar-based catalysts are discussed with regards to three aspects based on the interaction mechanisms, namely, oxidation, reduction, and photocatalysis. The synthesis conditions and loading of metal/metal-free catalyst are key parameters controlling the catalysis activity of biochar and biochar-based catalysts. This review provides new insights into the application of biochar in catalysis. Key challenges and further research directions are proposed as well. Image 1 • Environmental application of biochar in catalysis can be carried out in three ways. • The EPFR of biochar reacted with O 2 to induce hydroxyl radicals (.•OH). • Biochars activate oxidants to generate.•OH and SO 4 •−. • Biochars act as an electron acceptor to improve the photodegradation capacity. • This review provides new insights into the application of biochar in catalysis. [ABSTRACT FROM AUTHOR]

Abstract The environmental risk of galaxolide (HHCB) spurs the need to develop efficient and economical removal technology. Although sorption is one of the best removal approaches, studies on sorption of HHCB by biochar were limited. With the purpose of combining the advantages of ball-milling and sorption technologies, six ball-milled biochars (BM-biochars) varied with biomasses and pyrolysis temperature were produced, characterized, and tested for HHCB removal from aqueous solution. At an initial HHCB concentration of 2 mg L−1, the unmilled and BM-biochars adsorbed 330–746 and 609–2098 mg kg−1 of HHCB, respectively. The increase in sorption capacities (about 3-fold increase) was mainly ascribed to the increase in BM-biochar's external and internal surface area, pore volume and pore size, and the exposure of the graphitic structure. The removal of HHCB by the BM-biochars increased with increasing pyrolysis temperature. For lower temperature biochar (300 °C wheat straw biochar, WS300), hydrophobic partitioning played a major role in HHCB sorption onto unmilled biochar (log K oc /log K ow value of WS300 was 0.772 at a C e of 1 mg L−1). Ball milling reduced the hydrophobicity of 300 °C biochar, which diminished the HHCB sorption. However, increased surface area, pore volume, pore size, and graphitic structure provided additional sorption sites, resulting in enhanced HHCB uptake (log K oc /log K ow value of BMWS300 was 1.23 at a C e of 1 mg L−1). For higher temperature biochars (500 and 700 °C), ball milling mainly enhanced HHCB sorption onto high temperature biochars via surface adsorption, π-π interaction, and pore filling. For WS500, 77.9% of HHCB removal was due to surface adsorption. Ball milling increased this percentage to 96.7% for BMWS500. This work highlighted the potential of ball milling as an excellent engineering method to improve biochar's sorption properties. Graphical abstract Unlabelled Image Highlights • BM-biochars were synthesized combining the advantages of ball-milling and biochar technologies. • Ball milling increased the external and internal surface area of biochars. • Ball milling increased sorption ability of biochars to HHCB. • 77.9% of HHCB removal was due to surface adsorption for WS500. • 96.7% of HHBC removal was due to surface adsorption for BMWS500. [ABSTRACT FROM AUTHOR]

The iron (Fe)-impregnated biochar (FBC), fabricated via thermal pyrolysis of corn straw treated with FeCl 3 , was investigated for the sorption characteristics and mechanisms of aqueous arsenate removal. Structural and morphological analysis showed that large quantity of iron oxide particles tightly grew within the porous matrix of biochar (BC) through iron-impregnation. Batch sorption experimental results showed that the composite, with larger surface area, more functional groups, and greater thermal stability, exhibited excellent As(V) adsorption efficiency of 6.80 mg/g compared to 0.017 mg/g for unmodified BC (a 400-fold increase). The adsorption kinetics data were fitted well by pseudo second-order model, and sorption isotherms of As(V) were simulated well by both Freundlich and Langmuir models. XRD and FTIR analysis suggested that electrostatic attraction and precipitation were dominant mechanisms for As(V) sorption. The As(V)-loaded FBC could be easily separated from the solution by a magnet at the end of the sorption experiment. The FBC showed excellent re-sorption capacity, which account for about 70% removal efficiency for the second and third reuse in As(V) sorption. Results from this study demonstrated the promise of FBC composite as an efficient, low-cost, environmentally friendly, and regenerable adsorbent for As(V) remediation. Capsule FBC showed enhanced As(V) sorption capacity, excellent re-sorption capacity, and could be easily separated by a magnet. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe 1 -N 1 -BC 1 composites were synthesized by carbothermal reduction at 300 – 900 °C. • Low- and high-temperature composites showed superior N and Fe, respectively. • Fe 1 -N 1 -BC 1 -300 removed Cr(VI), and Fe 1 -N 1 -BC 1 -700 removed NB completely from solution. • Fe 1 -N 1 -BC 1 composites showed better efficiency in simultaneous removal of Cr(VI) and NB. • Fe 1 -N 1 -BC 1 composites exhibited restored removal capacity for more than four months. Synthesizing new composites with better efficiency and stability from abundant sources offers an appealing prospect for removal of heavy metals and organic pollutants to address water pollution concerns. In this study, iron (Fe) and nitrogen (N) doped biochar (BC) composites were investigated for hexavalent chromium (Cr(VI)) and nitrobenzene (NB) removal. Specifically, temperature-dependent Fe 1 -N 1 -BC 1 composites were synthesized with different mass ratios of FeCl 3 as Fe, melamine as N, and pinewood sawdust (PWS) as BC precursors via carbothermal reduction at 300, 500, 700, and 900 °C. Detailed characterizations indicating low-temperature incorporated superior N and high-temperature incorporated more Fe species in Fe 1 -N 1 -BC 1 composites. The Cr(VI) and NB were removed with Fe 1 -N 1 -BC 1 , and experimental results attested with standard isotherm and kinetic models. The N species (pyridinic-N, pyrrolic-N, graphitic-N, quaternary-N, and oxidized-N) and Fe species (Fe 3 C, Fe0, Fe 2p 3/2 , and Fe 2p 1/2) in temperature-dependent Fe 1 -N 1 -BC 1 composites participated in pollutants removal. Mass ratio of 1:1:1 of Fe, N, and BC was effective, and under optimum conditions, low-temperature (Fe 1 -N 1 -BC 1 -300) and high-temperature (Fe 1 -N 1 -BC 1 -700) composites completely removed Cr(VI) and NB, respectively. In comparison to pinewood sawdust BC (PWBC) and composite of FeCl 3 with PWS (Fe-BC), melamine with PWS (N-BC), and FeCl 3 with melamine (Fe-N), the Fe 1 -N 1 -BC 1 was more efficient due to synergistic effect of Fe, N, and BC for better pollutant interaction and removal. Effect of different factors on pollutants removal with Fe 1 -N 1 -BC 1 was studied to reveal removal mechanism insights. Additionally, Fe 1 -N 1 -BC 1 showed better efficiency in simultaneous removal of Cr(VI) and NB, stability for > 4 months, reusability, and applicability for multiple pollutants. This study offers a benign approach for synthesizing and applying Fe 1 -N 1 -BC 1 for pollutants removal and exploring reaction mechanisms. [ABSTRACT FROM AUTHOR]

[Display omitted] • Unique porous structure promotes mass transfer process to accelerate reaction kinetics. • N defect regulates the local electron density of active center Ni to enhance CO 2 adsorption. • Nitrogen atoms anchor Ni sites accurately, exposing more catalytic active sites. • Evaluating the optimal performance of the catalyst by changing the mass ratio and preparation temperature. Molecular catalysts have been receiving extensive attention due to their explicit, designable, easily modifiable molecular structures and tunable catalytic active sites, which exhibit elegant electrocatalytic performance in electrocatalytic carbon dioxide reduction reactions. However, the susceptibility to aggregation due to strong intermolecular π-π interactions among the metal bipyridines, phthalocyanines and porphyrins among the molecular catalysts limits their catalytic performance. Herein, an active catalyst nickel phthalocyanine anchored N-doped ball milled biochar (NiPc/N-BMBC) was developed with highly enriched pore structure and high surface area for electrocatalytic CO 2 reduction reaction. On the nanoscale, NiPc molecules were uniformly anchored on N-BMBC to enhance the dispersion, exposing sufficient catalytic active sites. Concretely, the catalyst NiPc/N-BMBC exhibited extraordinary performance in the electrolytic conversion of CO 2 reduction reaction, with a Faredaic efficiency of CO (FE CO) > 70 % at an overpotential (−0.75 to −0.95 V vs. RHE) and a high CO partial current density (j CO) of 96 mA cm−2 at −1.0 V vs. RHE, which were much higher than that of NiPc (24 %, 38 mA cm−2) and N-BMBC (9 %, 2 mA cm−2). This work provides a new insight in the structural design of carbon-based electrocatalyst for efficient electrocatalytic CO 2 reduction reaction. [ABSTRACT FROM AUTHOR]

• Na 2 S 2 O 4 , biochar, and micron iron were reunited by wet and dry ball milling. • Wet ball milling promoted faster and complete Cr(VI) removal (100 % in 80 min) • The composite of wet ball milling presented excellent anti-ageing property. • Higher electron selectivity was obtained (59.15% for wet and 46.72% for dry) • Replacing oxides with sulfides facilitated high iron cycling for Cr(VI) removal. Obstacles such as aggregation and low activity of micron zero-valent iron in pollutant treatment could be overcome by sulfidation and biochar support. Ball milling is a promising method for the preparation of iron-based composites but the milling atmosphere is critical. To maximize the reactivity and identify the effects of ball mill atmosphere, ball milling technology under wet and dry atmosphere was applied to prepare composites from mZVI, Na 2 S 2 O 4 , and pine wood biochar (BC) for Cr(VI) removal. The results showed that S-mZVI/BC-wet was highly dispersible with more FeS 2 coverage and thus more efficient on Cr (VI) removal than S-mZVI/BC-dry (99.9 % removal in 80 min vs. 87.9 % removal in 24 h) at the optimum Fe: C mass ratio (1:1), S: Fe molar ratio (1:10), and reaction conditions. Cr(VI) was adsorbed by a spontaneous, endothermic mechanism that combined physisorption and chemisorption. The reduction process was vulcanization efficiency and iron cycle dependent. Reduction outperformed adsorption on the Cr(VI) removal and high reduction rateswere electron-selectively related (59.15 % for S-mZVI/BC-wet and 46.72 % for S-mZVI/BC-dry), implying S-mZVI/BC-wet was more capable. S-mZVI/BC-wet presented excellent anti-ageing property and slightly inferior regeneration performance. In conclusion, the composite prepared by wet ball milling have excellent performance in rapid and complete removal of Cr(VI), and S-mZVI/BC-wet has superior potential in acidic wastewater treatment. [ABSTRACT FROM AUTHOR]

• The conductivity and conjugated O-containing functional groups of BMBCs(ball mill biochar) at higher pyrolysis temperature (≥ 700 °C) were responsible for synergistic effect with MR-1. • Low electronegative charges of BMBC700 and BMBC800 were more beneficial to the synergistic interaction with MR-1. • Cr(VI) removal reaction of MR-1 with BMBCs could be classified into two steps-fast reaction and slow reaction. Biochar, carbonaceous material produced from biomass pyrolysis, has been demonstrated to have electron transfer property (associated with redox active groups and multi condensed aromatic moiety), and to be also involved in biogeochemical redox reactions. In this study, the enhanced removal of Cr(VI) by Shewanella oneidensis MR-1(MR-1) in the presence of biochars with different pyrolysis temperatures (300 to 800 °C) was investigated to understand how biochar interacts with Cr(VI) reducing bacteria under anaerobic condition. The promotion effects of biochar (as high as 1.07~1.47 fold) were discovered in this process, of which the synergistic effect of BMBC700(ball milled biochar) and BMBC800 with MR-1 was noticeable, in contrast, the synergistic effect of BMBCs (300–600 °C) with MR-1 was not recognized. The more enhanced removal effect was observed with the increase of BMBC dosage for BMBC700+MR-1 group. The conductivity and conjugated O-containing functional groups of BMBC700 particles themselves has been proposed to become a dominant factor for the synergistic action with this strain. And, the smallest negative Zeta potential of BMBC700 and BMBC800 is thought to favor decreasing the distance from microbe than other BMBCs. The results are expected to provide some technical considerations and scientific insight for the optimization of bioreduction by useful microbes combining with biochar composites to be newly developed. [Display omitted] [ABSTRACT FROM AUTHOR]

As a natural reduction mineral, pyrite (FeS 2), was combined with biochar by simply ball milling technology to synthesize FeS 2 @biochar composite (BM-FeS 2 @BC) and applied for the removal of hexavalent chromium (Cr(VI)) in aqueous solution. SEM, XRD, FTIR, and XPS characterization results showed that the FeS 2 and biochar were successfully combined and biochar suppressed the agglomeration of FeS 2. Batch sorption experiments showed that the BM-FeS 2 @BC700 composite (mass ratio of FeS 2 -to-biochar = 3:1) had enhanced Cr(VI) removal capacity of 134 mg·g−1, which were 3–25 times higher than those of the corresponding pristine and ball-milled biochar and FeS 2. The removal of Cr(VI) by BM-FeS 2 @BC700 was dosage and pH dependent. The addition of oxalic acid (OA) exhibited a promotion effect on the removal of Cr(VI) by increasing the removal rate of Cr(VI) from 56% to 100%. Reduction, adsorption, and surface complexation were the dominate mechanisms for Cr(VI) removal by BM-FeS 2 @BC700. At the equilibrium Cr(VI) concentration of 15.7 mg·L−1, 92.25% of Cr(VI) was removed through reduction/precipitation and 8.75% was removed by adsorption/surface complexation. The fitting results of the Langmuir model proved that the removal of Cr(VI) by BM-FeS 2 @BC700 composite was chemical surface monolayer adsorption. This work demonstrates the potential of ball milling for the preparation of FeS 2 @BC composite to remove Cr(VI) from water and wastewater. [Display omitted] • Preparation of BM-FeS 2 @BC700 achieved the reuse of waste. • Ball milling inhibited the oxidation of the pyrite surface. • BM-FeS 2 @BC dramatically increased the uptake of Cr(VI). • Adsorption and reduction were the main mechanisms to remove Cr(VI). • Acidic pH was more beneficial to the reduction of Cr(VI). [ABSTRACT FROM AUTHOR]

Soil mercury contamination poses health risks. However, effective immobilization techniques are lacking with challenges including low efficiency, limited long-term stability, susceptibility to multi-medium interference, and difficulty in controlling health risks. This study confirmed the feasibility of thiol-modified biochar, and elucidated the underlying mechanisms. Within 32 days of treatment, the leachable mercury decreased from 184.7 μg/L to below the hazardous waste threshold (100 μg/L, HJ/T299–2007, China). After 198 days of treatment, the soil achieved a safe ecological state with a mercury immobilization rate of 79.8–98.2% and a 50% reduction in available methylmercury. Thiol-modified biochar facilitated the conversion of active mercury species (exchangeable, carbonate, and oxide) into stable forms (organic and residual) through complexation and precipitation (e.g., HgS). Soil quality improvements were observed, including enhanced cation exchange capacity, available nitrogen, and total organic carbon. Thiol-modified biochar exhibits long-term effectiveness. After one and two years of treatment, the leachable mercury remained within acceptable health risk limit (hazard quotient < 1) for adults and children, respectively. After three years, the leachable mercury met the Level III groundwater quality standard (< 1 μg/L, GB 14848–2017, China). This study demonstrates an effective strategy for long-term diminishing mercury mobility and health risks in soil. [Display omitted] • Thiol-modified biochar effectively reduces the mobility of mercury in soil. • Mercury is mainly immobilized in organic-bound and residual fractions. • Multilayer structures trap more mercury than porous structures. • Ecological and health risks of mercury decrease with improved soil fertility. • Mercury immobilization exhibits long-term stability. [ABSTRACT FROM AUTHOR]

Drought conditions and nutrients loss have serious impacts on soil quality as well as crop yields in agroecosystems. New techniques are needed to carry out effective soil water and nutrient conservation and fertilizer application tools. Here, calcium alginate (CA) beads impregnated with ball-milled biochar (BMB) were investigated as a new type of water/nutrients retention agent. Both CA and Ca-alginate/ball milled biochar composite (CA-BMB) beads showed high kinetic swelling ratios in KNO 3 solution and low kinetic swelling ratios in water, indicating that CA-BMB beads have the potential to retain mineral nitrogen and nutrients by ion exchange. Pseudo-second-order kinetic model well-described the swelling kinetics of both beads in KNO 3 solution. Over a range of temperatures, the characteristics of dehydration suggested that impregnation with BMB improved the water holding capacity and postponed the dehydration time of Ca-alginate. The cumulative swelling and release characteristics of water, K + , and NO 3 − indicated that CA-BMB beads have great potential as a soil amendment to improve its nutrient retention and water holding capacity. [ABSTRACT FROM AUTHOR]

Photocatalytic oxidation technology holds promise for ideal advanced treatment of antibiotic wastewater. Single-atom catalysts (SACs) are a new hotspot in catalytic science, but the photochemical studies on the removal of antibiotics from water and biocompatibility after entering the environment are scarce. In this work, we prepared a single Mn atom immobilized on N-doped biochar (Mn@N-Biochar) by impregnation calcination method for enhancing photocatalytic degradation of sulfanilamide (SNM) in different types of various water systems. Compared with the original biochar, Mn@N-Biochar showed enhanced SNM degradation and TOC removal capacity. DFT calculation concluded that the electrons of d‐orbital (Mn) and p-orbital (N) altered the electronic structure of biochar and enhanced the photoelectric performance. It was shown that Mn@N-Biochar caused negligible systemic inflammation and tissue damage when given orally in mice, and also did not alter cell death and ROS production in human lung, kidney, and liver cells, as compared with biochar. We are convinced that Mn@N-Biochar could enhance the photocatalytic degradation of antibiotics while maintaining biocompatibility, which could be a promising strategy for wastewater treatment. [Display omitted] • Mn@N-Biochar enhanced adsorption-photodegradation of SNM in lake, tap, and DI water. • The d orbitals of Mn and p orbitals of N tuned the electronic structure of biochar. • Mn@N-Biochar caused negligible cytotoxicity, systemic inflammation, and organ damage. • Mn@N-Biochar exhibited high catalytic activity while maintaining biocompatibility. [ABSTRACT FROM AUTHOR]

Over the past decade, biochar-supported nZVI composites (nZVI/biochar) have been developed and applied to treat various pollutants due to their excellent physical and chemical properties, especially in the field of chromium (VI) removal. This paper reviewed the factors influencing the preparation and experiments of nZVI/biochar composites, optimization methods, column experimental studies and the mechanism of Cr(VI) removal. The results showed that the difference in raw materials and preparation temperature led to the difference in functional groups and electron transfer capabilities of nZVI/biochar materials. In the experimental process, pH and test temperature can affect the surface chemical properties of materials and involve the electron transfer efficiency. Elemental doping and microbial coupling can effectively improve the performance of nZVI/biochar composites. In conclusion, biochar can stabilize nZVI and enhance electron transfer in nZVI/biochar materials, enabling the composite materials to remove Cr(VI) efficiently. The study of column experiments provides a theoretical basis for applying nZVI/biochar composites in engineering. Finally, the future work prospects of nZVI/biochar composites for heavy metal removal are introduced, and the main challenges and further research directions are proposed. [Display omitted] • NZVI/biochar is a highly efficient Cr(VI) removal composite. • Pyrolysis temperature and feedstock affect functional groups and electron transfer ability. • More efficient and stable effects can be achieved by adding stabilizer and element doping. • Flow rate is the key factor affecting removal efficiency in column experiment. • Multiple removal mechanisms coexist in nZVI/biochar Cr(VI) removal. [ABSTRACT FROM AUTHOR]

In order to synthesize biochar with the enhanced adsorption of inorganic mercury (Hg(II)) and organic mercury (Methylmercury, MeHg), biochars pyrolyzed at different pyrolysis temperatures (300, 500, and 700 °C) were ball milled with 3-trimethoxysilylpropanethiol (3-MPTS). Characterization results showed that 3-MPTS acted as an activator which further enlarged pores in biochars and ball-milling increased surface area of biochars. During ball milling, oxygen-containing functional groups increased which facilitated the loading of –SH group. The maximum adsorption capacities for Hg(II) adsorption in ball mill sulfhydryl modified biochars of 300, 500, and 700 °C were 401.8, 379.6 and 270.6 mg/g, respectively; simultaneously, the maximum adsorption capacity of MeHg was 108.16, 85.27 and 39.14 mg/g, respectively, which showed preferential increasing of 5.54 times on MeHg compared to the non-thiol modified biochar at low pyrolysis temperature of 300 °C. Results of kinetic adsorption experiments suggested that sorption data fitted well with Pseudo-second-order kinetic model, which proved that the mainly rate-limiting adsorption step was surface diffusion. Langmuir isotherm model fitting result showed that ligand exchange, surface complexation, surface adsorption and electrostatic attraction are dominant removal mechanisms. The 3-MPTS content and ball milling time are crucial during ball milling, and 2% 3-MPTS and 30 h of ball milling were found to be the most suitable conditions for both Hg(II) and MeHg adsorption. The result suggests that ball milling aided thiol-modification has great potential in synthesis of –SH modified biochar with prioritized MeHg adsorption. [Display omitted] • Ball milling can be successfully used for thiol modification of biochar by 3-MPTS. • Biochar pyrolyzed at lower temperature facilitated the loading of –SH group. • Thiol groups greatly enhanced the selectivity to MeHg as compared to Hg(II). • Thiol group is mainly loaded on biochar surface through –OH, C–O and C O. [ABSTRACT FROM AUTHOR]