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In this study, a newly developed composite of biochar-poly(m-phenylenediamine) (BC-PmPD) exhibiting a distinct skeletal structure was synthesized for the purpose of extracting Cr(VI) from aqueous solutions. BC was employed as a supportive carrier onto which PmPD nanoparticles were uniformly affixed through in-situ polymerization and oxidation synthesis, both within and outside the layered configuration of BC. The structural stability and morphologies of BC-PmPD were assessed utilizing Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, thermogravimetric analysis, analysis of specific surface area and pore size, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. In comparison to other modified BCs reported, BC-PmPD exhibited the highest Cr(VI) removal rate. Specifically, at 303 K, BC-PmPD achieved a maximum Cr(VI) removal capacity of 775 mg g−1, surpassing the capabilities of unmodified BC and PmPD by 10.4 and 2.13 times, respectively. Analyses involving XPS, FTIR, and density functional theory calculation confirmed that proton transfer happened between protonated amine (−NH2) functional group within the structure of BC-PmPD and HCrO4− before the formation of hydrogen bond. Subsequently, environmentally persistent free radicals facilitated the reduction of the adsorbed Cr(VI). Quantification of the functional groups indicated that the amino group was responsible for 93.0% of the Cr(VI) adsorption in BC-PmPD. BC-PmPD displayed potent adsorption and reduction capabilities, alongside notable stability, repeatability, and promising potential for application in the remediation for high concentrations of Cr(VI) in electroplating wastewater scenarios. Highlights: Novel 3D material was prepared and the removal rate of Cr(VI) on BC-PmPD was the highest as compared to reported BCs. The maximum adsorption amount of Cr(VI) on BC-PmPD was high up to 1034 mg g−1 at 323 K and −NH2 adsorbed 93.0% HCrO4–. DFT calculation confirmed proton transfer happened between protonated −NH2 and HCrO4− before the formation of H bond. [ABSTRACT FROM AUTHOR]

Pyrolyzing sludge into biochar is a potentially promising recycling/disposal solution for municipal wastewater sludge, and the sludge-derived biochar (SDBC) presents an excellent sorbent for metal immobilization. As SDBC is composed of both mineral oxides and carbonized organic compartment, this study therefore compared the sorption behaviour of Pb and Zn on SDBC to those of individual and mixture of activated carbon (AC) and amorphous aluminium oxide (AlO). Batch experiments were conducted at 25 and 45 °C, and the metal-loaded sorbents were artificially aged in the atmosphere for 1-60 days followed by additional sorption experiments. The Pb sorption was generally higher than Zn sorption, and the co-presence of Pb reduced Zn sorption on each studied sorbent. Higher sorption capacities were observed at 45 °C than 25 °C for SDBC and AC, while the opposite was shown for AlO, indicating the significance of temperature-dependent diffusion processes in SDBC and AC. Nevertheless, metal sorption was more selective on AlO that showed a greater affinity towards Pb over Zn under competition, correlating with the reducible fraction of sequential extraction. Furthermore, significant amounts of Pb and Zn were additionally sorbed on SDBC following 30-day ageing. The X-ray diffraction revealed the formation of metal-phosphate precipitates, while the X-ray photoelectron spectroscopy showed a larger quantity of metal-oxygen bonding after 30-day ageing of metal-loaded SDBC. The results may imply favourable long-term transformation and additional sorption capacity of SDBC. In conclusion, SDBC resembles the sorption characteristics of both organic and mineral sorbents in different aspects, presenting an appropriate material for metal immobilization during soil amendment. [ABSTRACT FROM AUTHOR]

Purpose: The purpose was to develop a netbag technique suitable for burying biochar in a compost or composting medium, followed by its collection in a clean state (i.e., free of compost debris) without loss or damage, for physicochemical analyses. Collection in a clean state is required to ensure that the analytical data of various biochars are representative and comparable. Five criteria were identified to evaluate the suitability of netbag. Materials and methods: A small netbag (3.5 × 3.5 cm) was developed using nylon fabric (30-μm mesh) to contain ∼1 g of biochar. A production system was developed to make 15 netbags per batch. Unlike commonly used litterbags, polypropylene was used to seal netbags. Two experiments were conducted in which three biochars, made from macadamia nutshell, hardwood shaving, and chicken litter, were co-composted with chicken manure and sawdust and also incubated with a chicken litter-based commercial compost. Biochars were added at the rates of 5 or 10 % in the co-composting and 10 or 20 % in the incubation experiments. The biochar-containing netbags were buried in the co-composting and incubation mediums for 133 days. Various physicochemical analyses were conducted with netbag-biochars and their compost mediums. Results and discussion: The netbags collected after both experiments showed no visible sign of degradation. The weight of netbag-biochars from co-composting and incubation systems did not reduce significantly over the experimental period, thereby indicating no loss of biochar. No visible evidence of entry of solid particles from compost medium was found on the netbag-biochars. Pretests indicated that the netbag and biochars absorbed pore solution from the medium. Findings showed that elements translocated between the netbag-biochar and compost medium. A colony of coccus bacteria was found on the surface of composted chicken litter biochar, denoting probable entry of bacteria from compost medium. Unlike conventional litterbags, the netbags were suitable for burying and extracting biochar in compost/composting mediums due to smaller size, smaller mesh, and strong sealing with polypropylene. Conclusions: The netbags addressed all the five criteria. Therefore, it was concluded that, in the co-compost or incubated-compost medium, the biochar retained in the netbag and the biochar mixed with the medium were exposed to a similar bio-oxidative environment, and netbag-biochar represents the biochar in the medium. This means that these netbags can be used as a convenient means to examine the effects of the composting process or incubation in compost on biochar. [ABSTRACT FROM AUTHOR]

[Display omitted] • An iron-carbon composite was prepared at a low-temperature (250 °C). • Fe(IV) was the main reactive species in the iron-carbon composite/PS system. • The existence of Fe(IV) were identified by in situ Raman, Mössbauer spectrum. • Fe(IV) formation processes under a wide range of pH conditions was explored. • Fe species promoted the formation of the graphitized structure of biochar. Fe(IV) is typically formed under acidic or neutral conditions while its formation mechanism and impacts on pollutant decomposition have been overlooked, particularly in persulfate (PS) systems. In this study, an iron-carbon composite (Fe-BC250) was prepared at a low-temperature (250 °C) to explore the PS activation and Fe(IV) formation processes under a wide range of pH conditions. Fe(IV) was the main reactive species in the iron-carbon composite/PS system, and Fe species promoted the graphitization of biochars. The existence of Fe(IV) in the Fe-BC250/PS system was identified by in situ Raman, Mössbauer spectrum, and methyl phenyl sulfoxide probe (PMSO) experiments. Under alkaline conditions, the solution pH decreased because hydrolyzed Fe2+ generated H+, and surface Fe(II) reacted with PS to form Fe(IV). The Fe-BC250/PS system was superior in removing contaminants under alkaline conditions compared to the Fe2+/PS system, due to the slow release of Fe2+ from Fe-BC250. This study offers new insights into the Fe(IV) formation mechanism in biochar/PS systems under a wide range of pH conditions and provides a theoretical basis for applying low-cost iron-carbon composites in water treatment. [ABSTRACT FROM AUTHOR]

• Metal-free biochar/PS can effectively degrade aniline aerofloat in mining water. • Defect and carbonyl group of biochar triggered O 2 •− and non-radical mechanisms. • Attacked sites of aniline aerofloat were verified by combining DFT method. • T.E.S.T software and seed germination showed less toxicity of AAF intermediates. Residual flotation reagents in mineral processing wastewater can trigger severe ecological threats to the local groundwater if they are discharged without treatment. Metal-free biochar-induced persulfate-advanced oxidation processes (KCBC/PS) were used in this study to elucidate the degradation of aniline aerofloat (AAF) – a typical flotation reagent. In KCBC/PS system, AAF can be removed at low doses of catalyst (KCBC, 0.05 g/L) and oxidant (PS, 0.3 mM) additions with high efficiency. The analysis revealed the dominance of O 2 •− among the identified reactive oxygen species (ROS), which achieved deeper mineralization for the AAF degradation in the KCBC/PS system. The role of the electron transfer mechanism was equally important; the importance was corroborated by the chemical quenching experiments, electron spin resonance (ESR) detection, probe experiments, and electrochemical analysis. It benefited from the electron transfer mechanism in the KCBC/PS system and exhibited a wide pH adaptation (3.5–11) and high resistance to inorganic anions for real mining wastewater treatment. Combined with theoretical calculations and other analyses, the carbonyl group was deemed to be the active site of the non-radical pathway of biochar, while the site of the conversion of SO 4 •− to superoxide radicals by biochar activation represented a defect. These findings revealed a synergistic effect of multiple active sites on PS activation in biochar-based materials. Moreover, the intermediate degradation products of AAF from mass spectrometry indicated a possible pathway through the density functional theory (DFT) method, which was effective in reducing the environmental toxicity of pollutants for the first time according to the T.E.S.T software and seed germination experiments. Overall, our study proposed a novel modification strategy for cost-effective and environmentally friendly biochar-based catalysts, while also deepening our understanding of the mechanism of activation of persulfate by metal-free carbon-based materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The activation of hemp stalk-derived homologous biochar-based catalysts with persulfate demonstrates distinct mechanisms, whereby porous biochar favors radical pathways and N-doped biochar utilizes non-radical electron transfer pathways, thereby highlighting their potential in the control of environmental pollution. [Display omitted] • Biochar (BC) and N-doped in biochar (NBC) are used to activate persulfate (PS). • N-doping leads to a different activation mechanism compared to BC. • BC-PS system operates a radical pathway with a removal rate of 89%. • NBC-PS system operates a non-radical pathway with a removal rate of 96%. Advancements in biochar activating persulfate advanced oxidation processes (PS-AOP), have gained significant attention. However, the understanding of biochar-based catalysts in activating PS remains limited. Herein, biochar (BC) and N-doped biochar (NBC) were synthesized from hemp for activating PS to treat tetracycline (TC) wastewater and analyzed their mechanisms separately. Surprisingly, N-doped in biochar leads to a change in the activation mechanism of PS. The BC-PS system operates mainly through a radical pathway, advantageous for treating soil organic pollution (68%) with pH adaptability (less than 10% variation). Nevertheless, the NBC-PS system primarily employs an electron transfer non-radical pathway, demonstrating stability (only 7% performance degradation over four cycles) and enhanced resistance to anionic interference (less than 10% variation) in organic wastewater treatment. This study provides a technical reference and theoretical foundation for enhancing biochar activation of PS in the removal of organic pollutants from aquatic and terrestrial environments. [ABSTRACT FROM AUTHOR]

The apple snail (Pomacea canaliculata Lamarck) is among the 100 worst invasive alien species worldwide. Apple snail residues discarded during daily management are potential raw materials for biochar production. This study optimized the factors for producing apple snail biochar (ASB) using response surface methodology (RSM) and analyzed the As removal capacity and soil remediation effects of the optimal ASB. The optimal ASB occurred for 348.63 °C pyrolysis temperature, 2.19 h pyrolysis time, and 2.53 Fe3+/Fe2+ molar ratio. For the optimal ASB, the maximum experimental As(III) removal ratio was 98.72%. Temperature and the Fe3+/Fe2+ molar ratio were essential factors affecting the As removal ratio of ASB. The ASB had a rough surface, and As (1.09%) was evident on its surface after adsorption. The As(III) adsorption capacity on ASB was 10.59 mg/g at 288 K, 9.75 mg/g at 298 K, and 11.82 mg/g at 308 K. The As immobilization efficiency in the 3% and 5% ASB treatments exceeded 50% after 15 d. The 5% ASB treatment increased the soil organic matter, total N, available N, total P, and available P content by 120%, 245%, 47%, 62%, and 154%, respectively. Within 15 d, the soil methane oxidation potential peaked at 4.05 μg/g/h in the 5% ASB treatment. The maximum methane oxidation rate occurred after 10 d in the 5% ASB treatment. ASB has multiple benefits for As immobilization, quality improvement, and methane oxidation in soil. This study provides a reference for optimized production and application of invasive animal biochar in contaminated soil. [Display omitted] • Invasive snail residues can be produced into As adsorbent using RSM. • Apple snail biochar effectively reduces the availability of As in soil. • Snail biochar improves the physicochemical properties of As-contaminated soil. • Methane oxidation potential of As-contaminated soil is enhanced by snail biochar. [ABSTRACT FROM AUTHOR]

N-doped porous carbon materials synthesized by one-step pyrolysis of hemp stems exhibits remarkable adsorption capacity for organic pollutants, and have great potential for efficient removal of organic pollutants from landfill leachate and soil. [Display omitted] • N-doped porous carbon (NBC) adsorbent is synthesized using hemp stems as the carbon source. • NBC demonstrates an excellent tetracycline adsorption capacity that is twice that of activated carbon. • The doping of pyrrolic-N enhances surface defects, electronegativity, and electron conductivity in NBC. • NBC adsorbs tetracycline primarily through cation-π and π-π interactions facilitated by pyrrolic-N. Nitrogen (N) doping is commonly used to modify biochar and enhance its adsorption performance. However, the significance of pyrrolic-N in pollutant adsorption is frequently overlooked. In this study, N-doped porous carbon materials (NBC) have been synthesized using hemp stems as the carbon source through pyrolysis in one step for the efficient removal of organic pollutants. The incorporation of the pyrrolic-N functional group in NBC leads to an increase in surface defects, electronegativity, and electron conductivity. As a result, the Q max of tetracycline (TC) reaches 577.60 mg/g, which is twice as much as activated carbon with a similar specific surface area. The characterization and theoretical calculation demonstrate that the NBC adsorbent adsorbs TC primarily through cation-π and π-π interactions facilitated by pyrrolic-N, as well as weak electrostatic interactions induced by –COOH. In actual landfill leachate adsorption experiments, the NBC effectively reduced chemical oxygen demand and ammonia–nitrogen levels in wastewater. Additionally, the growth of sprouts planted on contaminated soil treated with NBC (sulfamethoxazole, 50 mg/kg) is restored to levels observed on uncontaminated soil, thus demonstrating its practicality. [ABSTRACT FROM AUTHOR]

A greenhouse experiment was conducted to examine the effects of urea hydrogen peroxide (UHP) on reducing the accumulation of As in rice grains. The results show that UHP effectively triggered Fenton-like reaction by reacting with Fe2+ in the paddy soils. This significantly inhibited the activities of As(V)-reducing microbes, causing impediment of As(V)–As(III) conversion following inundation of dryland crop soils for paddy rice cultivation. As-methylating microbes were also inhibited, adversely affecting As methylation in the soils. These processes led to the reduction in phyto-availability of As in the soil solutions for uptake by rice plant roots, and consequently reduced the accumulation of As in the rice grains. In this study, an UHP application rate of 0.0625% on three occasions (tillering, heading and filling) during the rice growth period was sufficient to lower the rice grain-borne As concentration to below 0.2 mg/kg, meeting the quality standard set by the Chinese government. No additive effect on reducing grain-borne As was observed for the joint application of UHP and biochar or biochar composite. The use of UHP for soil fertilization had no adverse impact on rice yield in comparison with the application of urea at an equal amount of nitrogen. • Urea hydrogen peroxide was a suitable alternative of N-fertilizer for rice growth. • It effectively triggered Fenton-like reaction to generate hydroxyl radical in soils. • Arsenate-reducing and As-methylating microbes were significantly inhibited. • Phytoavailability of soil-borne As was significantly reduced in its presence. • This markedly impeded As accumulation in rice grains without affecting rice yield. [ABSTRACT FROM AUTHOR]

Biochar amendment can be adopted to improve soil substrate, in turn facilitated phytoremediation. However, improvements to the properties of tailings following different feedstocks of biochar amendment in phytoremediation, particularly the impacts on nitrogen cycle and the related nitrogen-fixing microorganisms remain unclear. In this study, a 100-day pot experiment was designed to determine the co-effects of different combinations of woody and non-woody biochar, namely hibiscus cannabinus core biochar (HB), sewage sludge biochar (SB), chicken manure biochar (MB) and two crops (Cassia alata L., Boehmeria nivea L.). It was found that, on the one hand, biochar amendment directly immobilized heavy metal (loid) contamination in the tailings; on the other hand, biochar amendment, particularly non-woody SB, improved soil properties (i.e., the combination of SB with crops increased the total nitrogen content by 4.7–7.5 times). This indirectly improved phytostabilization (i.e., SB increased crop height 1.5–1.8 fold, root length 3.3–3.7 fold, decreased NH 4 NO 3 -extractable Pb, Cu, Cd and also increased the relative abundance of nitrogen-fixing bacteria such as Mesorhizobium , Bradyrhizobium , and Rhizobium). Besides this, redundant analysis shown that the carbon, nitrogen sources, and pH provided by the biochar were identified as the key factors associated with the nitrogen-fixing bacteria. Through the comprehensive evaluation of different biochar amendment in phytoremediation, it was found that the non-woody SB got higher comprehensive score (3.1–3.6) in biochar amendment in phytoremediation, especially in Boehmeria nivea L. Thus, the combination of non-woody SB and Boehmeria nivea L. improved microbial function, while the microorganisms in turn promoted crop growth. Our results revealed the prospect of using non-woody SB assisted Boehmeria nivea L. for phytoremediation in multi-metal mine tailings. [Display omitted] • Sewage sludge biochar assisted Boehmeria nivea L. recovered the tailings ecosystem. • The nitrogen retention and abundance of nitrogen-fixing bacteria was increased. • The C, N, and pH were the key factors associated with the nitrogen-fixing bacteria. • The mechanisms of biochar amendment in phytoremediation are proposed. [ABSTRACT FROM AUTHOR]

Highlights • Cr(VI) removal efficiency by TPBC was weakened by pyrolytic temperature increase. • The reduction of Cr(VI) was mainly affect by carboxyl group. • Adsorption-reduction-adsorption process was simulated based on apparent kinetics. • Cr(VI) removal was kinetic controlled by Cr(VI) and Cr(III) adsorptions. Abstract Tobacco petiole biochar (TPBC) was prepared via pyrolysis and used for Cr(VI) removal. Cr(VI) removal efficiency was reduced by pyrolytic temperature (PyT) increase which mainly affected by functional groups rather than specific surface area. According to the optimal pseudo second-order kinetic, the initial adsorption rate was decreased with PyT increase from 355.91 mg·g−1·min−1 (PyT = 300 °C) to 3.44 mg·g−1·min−1 (PyT = 700 °C). The isotherm was optimally explained by Temkin model involved physical absorption with heat of 28.73 J/mol. Simulation result of adsorption-reduction-adsorption process showed the Cr(VI) removal was kinetic controlled by Cr(VI) and Cr(III) adsorptions. TPBC300 was the optimal TPBC for chromium removal from electroplating wastewater with efficiencies of: 66.7% (Cr(VI)) and 21.1% (Cr(tot)). [ABSTRACT FROM AUTHOR]

After the application of sludge derived biochar (SDBC) for soil stabilization, it is subjected to continuous leaching that may change its surface properties and metal(loid) immobilization performance. This study simulated the continuous leaching through the fresh SDBC sample in columns with unsaturated and saturated zones under flushing with 0.01 M NaNO 3 solution (pH 5.5) and acidic solution (pH adjusted to 3.2 by HNO 3 :H 2 SO 4 = 1:2), respectively. The resultant changes were assessed in terms of the SDBC surface characteristics and metal(loid) sorption capacities. Continuous leaching was found to gradually decrease the density of basic functional groups and increase the density of carboxyl groups as well as cation exchange capacity on the SDBC surface. It was attributed to the surface acidification and oxidation process by the leaching process, yet it occurred to a lesser extent than the atmospheric exposure. Continuous leaching increased Pb(II), Cr(VI), and As(III) sorption capacity of the SDBC, probably because the increase in carboxyl groups promoted inner-sphere complexation and Fe oxidation as revealed by spectroscopic analysis. It was noteworthy that the SDBC in the unsaturated and saturated zones under continuous leaching displayed distinctive effects on metal(loid) sorption capacity than the atmospheric exposure. Future investigations are needed for understanding the fate and interactions of the SDBC under varying redox conditions and intermittent leaching process. [ABSTRACT FROM AUTHOR]

The present study investigated the co-transport behavior of three REEs3+ (La3+, Gd3+, and Yb3+) with and without biochar nanoparticles (BC NPs) in water-saturated porous media. The presence of REEs3+ enhanced the retention of BC NPs in quartz sand (QS) due to decreased electrostatic repulsion between BC NPs and QS, enhanced aggregation of BC NPs, and the contribution of straining. The distribution coefficients (K D) in packed columns in the co-transport of BC NPs and three REEs3+ were much smaller than in batch experiments due to the different hydrodynamic conditions. In addition, we, for the first time, found that REE fractionation in the solid-liquid phase occurred during the co-transport of REEs3+ in the presence and absence of BC NPs. Note that the REE fractionation during the co-transport, which is helpful for the tracing application during earth surface processes, was driven by the interaction of REEs3+ with QS and BC NPs. This study elucidates novel insights into the fate of BC NPs and REEs3+ in porous media and indicates that (i) mutual effects between BC NPs and REE3+ should be considered when BC was applied to REE contaminated aquatic and soil systems; and (ii) REE fractionation provides a useful tool for identifying the sources of coexisting substances. [Display omitted] • REE fractionation occurs during the co-transport with and without BC NPs. • Both quartz sand and BC NPs result in more Yb3+ enrichment during the co-transport. • REE fractionation in their co-transport is subject to the lanthanide contraction. • Mutual effects between BC NPs and REEs3+ are found in their co-transport. • Batch tests overestimate the adsorption of REEs3+ by BC NPs compared to column data. [ABSTRACT FROM AUTHOR]

Biochar is being widely considered as a promising amendment agent for immobilizing heavy metals in contaminated acidic soils, where plenty of soluble Al(III) ions exist. In view of uncertain significance of the effects of coexisting Al(III) on Pb(II) sorption by biochars, this study used kenaf core biochar (KB550; high carbon, low ash) and sewage sludge biochar (SB550; low carbon, high ash) pyrolyzed at 550 °C to elucidate the influence of coexisting Al(III) species and biochars’ mineral components on Pb(II) immobilization conducted in aqueous solution with initial pHs of 3.0–4.5. Results showed that Al(III) reduced Pb(II) sorption on KB550 primarily via pH buffering against biochar alkalinity, thus inhibiting lead carbonate formation. In contrast, the reduction on SB550 mainly resulted from direct competition for sorption sites, especially on Fe-rich phengite 2 M 1 and metakaolinite. Because of Pb-P precipitation and Pb-K interlayer exchange, the residual Pb(II) adsorption capacity resistant to coexisting Al(III) was 3–5 times higher on SB550 than on KB550. The Pb-K interlayer exchange was enhanced by lower pH and coexisting Al(III), while Pb-P precipitation was the dominant Pb(II) sorption mechanism on SB550 resistant to Al(III) buffering and competition at higher pH. Application of these two biochars as amendments confirmed that the mineral-rich SB550 was more suitable for Pb(II) immobilization in acidic soils with high levels of extractable Al(III). [ABSTRACT FROM AUTHOR]

Currently, sludge pyrolysis has been considered as a promising technology to solve disposal problem of municipal sewage sludge, recover sludge heating value, sequester carbon and replenish nutrients in farmland soils. The resultant sludge-derived biochar (SDBC) is potentially an excellent stabilizing agent for metal species. This study applied the SDBC into four soils that had been contaminated in field with cationic Pb(II) and Cd(II)/Ni(II), and anionic Cr(VI) and As(III), respectively. The performance of metal stabilization under various operational and environmental conditions was evaluated with acid batch extraction and column leaching tests. Results indicated the SDBC could effectively stabilize these metals, which was favored by elevated temperature and longer aging. Periodic temperature decrease from 45 to 4 °C resulted in the release of immobilized Cr(VI) and As(III) but not Pb(II). However, a longer aging time offset such metal remobilization. This was possibly because more Pb was strongly bound and even formed stable precipitates, as shown by XRD and sequential extraction results. With increasing time, Cr(VI) was sorbed and partly reduced to Cr(III), while immobilized As(III) was co-oxidized to As(V) as indicated by XPS spectra. Column tests revealed that adding SDBC as a separate layer was unfavorable because the concentrated Cd(II) and Ni(II) in localized positions increased the peak levels of metal release under continuous acid leaching. In contrast, uniformly mixed SDBC could effectively delay the metal breakthrough and reduce their released amounts. Yet, a long-term monitoring may be required for evaluating the potential leaching risks and bioavailability/toxicity of these immobilized and transformed species in the SDBC-amended soils. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe enhanced the redox conversion of Cr(VI) and As(III). • Fe accounted for 18.9%–47.4% and 98.1%–99.4% of the removed Cr(VI) and As(III). • Cr(VI) was adsorbed by the C-OH groups, and As(III) was bonded to γ-FeOOH. • Fe0, Fe2+, H*, and O-containing groups contributed to the reduction of Cr(VI). • •OH, •O 2 −, 1O 2 , and Fe(OH) 3 were responsible for the oxidation of As(III). Fe-based materials have been widely used for removing Cr(VI) and As(III) in wastewater, however, the quantitative understanding of their removal mechanism and functions of Fe is lacking. In this study, three types of iron carbide based biochar composites (Fe 3 C@BC-A, Fe 3 C@BC-B, and Fe 3 C@BC-C) with different Fe dosages of 19.7%, 24.0%, and 26.5%, respectively, were prepared for Cr(VI) and As(III) removal. The removal of Cr(VI) and As(III) was found to increase as the Fe dosage increased. Fe 3 C@BC-C with the highest Fe content showed the greatest reduction and oxidation capacities for Cr(VI) and As(III). X-ray absorption near-edge structure analysis indicated that the reduction of Cr(VI) afforded FeCr 2 O 4 , (Cr x Fe 1-x)(OH) 3 , Cr3+, Cr(OH) 3 , and Cr 2 O 3 , whereas AsO 4 3- was the oxidation product of As(III). Results of a pickling experiment revealed that Fe accounted for 18.9%–47.4% and 98.1%–99.4% of the removed Cr(VI) and As(III), respectively. The adsorption mechanism revealed by Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy (XPS) suggested that Cr(VI) was adsorbed by the OH groups of biochar, whereas As(III) was bonded to γ-FeOOH of the reacted Fe 3 C particles. The quenching experiment, electron spin resonance analysis, and XPS suggested that Fe0, Fe2+, atomic H, and O-containing groups contributed to the reduction of Cr(VI), while •OH, •O 2 −, 1O 2 , and Fe(OH) 3 were responsible for the oxidation of As(III). The quantitative mechanisms contributed to an improved understanding for the removal of Cr(VI) and As(III) by Fe/C composites, and the results may guide further preparation and application of Fe/C composites for redox-active contaminants removal. [ABSTRACT FROM AUTHOR]

Sludge derived biochars (SDBCs) may have the potential to simultaneously remove heavy metals and organic contaminants in relation to their various active sorption sites for both metal ions and organic compounds. SDBCs have been proven to provide a considerable capacity for immobilizing Pb(II) and Cr(VI) ions in solution, and in this study their ability to sorb atrazine, in addition to their corresponding interactive influences with coexisting metal ions, is extensively investigated. The results indicate that all atrazine adsorption isotherms fit well with the Freundlich equation, and the greatest value of 16.8 mg g −1 sorption capacity occurred with SDBCs pyrolyzed at 400 °C for 2 h. The slow sorption kinetics fit well with the Lagergren’s 2nd order reaction, and depend upon the initial atrazine concentration, indicating the significance of a site-specific process. The ionic strength-dependence of the atrazine adsorption behavior further consolidates the involvement of the mechanism of the H-bond with hydroxyl groups on SDBC. However, when Pb(II)/Cr(VI) metal ions coexist in solution, they substantially suppress atrazine adsorption, probably because the inner complex between the hydroxyl groups on SDBCs and Pb(II)/Cr(III) ions intrude the weak H-bond with atrazine. As a result, metal adsorption was found to be unaffected by the coexisting atrazine. Therefore, although SDBC is applicable for atrazine removal/immobilization in most of environmentally relevant conditions, a two-step process may be required if heavy metal ions coexist. [ABSTRACT FROM AUTHOR]

Zero valent iron (Fe0) has been used to remove organic contaminants. However, its low utilization efficiency and high toxicity have hindered its application. In this study, Fe 3 C@Fe0-loaded biochar (Fe 3 C@Fe0@BC) with 40.1% Fe content and slight Fe release presented excellent removal efficiency, stability, and reusability for tetracycline hydrochloride (TH). Fe 3 C@Fe0@BC presented selective oxidation degradation to TH in real wastewater and eliminated 99.1% of TH after a 12 h treatment, which considerably exceeded the removal action of fresh Fe0 and biochar. Radical scavenger experiments, desorption experiments, and electron paramagnetic resonance analysis confirmed that the removal of TH on Fe 3 C@Fe0@BC was mainly mediated by degradation and the Fe utilization efficiency was high up to 214%. TH degradation pathways and hydroxylation reactive sites were explored using high-performance liquid chromatography-mass spectrometry and density functional theory modeling. The acute toxicity of TH solution after Fe 3 C@Fe0@BC treatment and that of the fresh or used materials on Daphnia magna was the lowest. Fe/C composites present a good alternative for Fe0 because of the high Fe utilization efficiency and low toxicity of the material and produced antibiotic degradation byproducts. This study presents important findings related to the toxicity of Fe/C composites and provides strong technical support for the practical application of Fe/C composites. [Display omitted] • Fe 3 C@Fe0@BC exhibited superior Fe utilization efficiency, stability and recycling. • Fe 3 C@Fe0@BC presented selective oxidation degradation to TH in wastewater treatment. • Potential degradation pathways of TH were demonstrated by HPLC-MS and DFT modeling. • Fe 3 C@Fe0@BC composite had the lowest toxicity as compared to Fe0 and biochar. • Toxicity of TH had been largely eliminated after treatment of Fe 3 C@Fe0@BC composite. [ABSTRACT FROM AUTHOR]

Highlights: [•] The sludge derived biochar is an excellent sorbent for Pb(II)/Cr(VI) ions. [•] 400°C for 2h seems the optimal conditions for biochar pyrolysis. [•] A long-time pyrolysis reinforces the Pb(II)/Cr(VI) sorption bond on biochar. [•] Cr(VI) sorption is highly pH-dependent, and the optimal occurs at pH 2. [•] Reducing Cr(VI) to Cr(III) is the main sorption mechanism on biochar. [ABSTRACT FROM AUTHOR]

Highlights: [•] The sludge obtained from WWTP with pure sewage is suitable for preparing biochars with high isoelectric point (IEP) and uniform charge distribution. [•] The pyrolysis temperature of 400°C was optimal to produce SDBC with more uniform surface charge distribution. [•] The pyrolysis temperature of 300°C resulted in the most reduction in DTPA-extractable metals in the SDBC. [•] Environmental risk of SDBC can be minimized and managed by controlling the source of feedstock and pyrolysis temperature. [ABSTRACT FROM AUTHOR]

Oxidized aging due to the long-term exposure can significantly alter the sorption of pyrogenic chars (i.e., biochar, BC) towards antibiotics, which determined their fates in natural environments. In this study, the sorption of ciprofloxacin (CIP) on the oxidizing-aged BCs was studied linking the experimental thermodynamics and theoretical calculations. Results revealed that Q 0 of CIP negatively correlated with their average site energies (E m), while pore-normalized Q 0 on aged BCs were 2–6 folds higher than fresh BCs. From competitive sorption, it is proposed that the transformation of CIP± to CIP+ occurred and the π+–π electron donor-acceptor interaction and Coulombic attraction onto the aged BCs played a critical role. These two specific interactions with CIP were thermodynamically improved when aging degree increased and favored the free energies (Δ a G) of sorption by 2–5 kJ mol−1. Based on the identified relationship between experimental Δ OA -Δ G 0 with E a through DFT calculations, the contributions of the specific interactions to antibiotic sorption on aged BCs were quantified. This study provided an in-depth understanding of how the aging process affects the sorption of zwitterionic antibiotics on BCs and also possibilities to predict the fate of antibiotics in the presence of BCs over a long-term period. [Display omitted] • Oxidized aging altered distribution of pores and delocalized π electrons on chars. • Pore-normalized Q 0 of CIP on aged chars were 2–5 folds higher than fresh chars. • π+–π interactions and Columbic forces thermodynamically favored by 2–5 kJ mol−1. • A valid relationship between experimental Δ OA -Δ G 0 with calculated E a established. [ABSTRACT FROM AUTHOR]

• Fe/Mn oxides loaded biochar could enhance the adsorption of tetracycline. • γ-Fe 2 O 3 and MnO 2 were the main crystalline phases of Fe/Mn oxides. • Fe/Mn oxides play complex acid and base roles to enhance the tetracycline adsorption. • Adsorption of tetracycline follow Elovich kinetic model and Langmuir isotherm. A Fe/Mn oxides loaded biochar (FeMn-BC) was prepared to enhance the adsorption of tetracycline (TC). γ-Fe 2 O 3 and MnO 2 were assigned to the Fe and Mn oxides, respectively. The enhanced adsorption of TC was dominated by the loaded γ-Fe 2 O 3 and MnO 2. According to Akaike-Information-Criteria evaluation, Elovich kinetic and Langmuir isotherm models could best describe the adsorption with a maximum capacity of 14.24 mg/g. During adsorption process, the γ-Fe 2 O 3 and MnO 2 hydrolyzed into hydroxides (FeOOH and MnOOH) which acted as bases to complex with TC2− ion under alkaline condition (pH = 11). After the adsorption, the concentrations of leached Fe and Mn could meet the requirements PRC standards GB13456-2012 and GB8978-1996, respectively. The FeMn-BC had ~24% on TC removal (initial concentration of 20 mg/L) after four-cycles regeneration. The FeMn-BC was also available for TC adsorptions in column tests and actual wastewater. [ABSTRACT FROM AUTHOR]

• Degradation of OTC was easier than that of CAP for C/Fe 3 C/Fe0 and Fe0. • C/Fe 3 C/Fe0 was an excellent ROS generator relative to Fe0. • OH was responsible for both the removal of OTC and CAP. • 1O 2 exhibited selective oxidation capacity to OTC as compared to CAP. • C/Fe 3 C/Fe0 showed superior stability and reusability for OTC and CAP. Reactive oxygen species (ROS) production for Fe0 is limited because of the formed iron corrosion products. In this study, C/Fe 3 C/Fe0 composite which produces enhanced ROS has been specifically designed and fabricated to remove typical antibiotics (i.e., oxytetracycline (OTC) and chloramphenicol (CAP)) as a heterogeneous Fenton-like catalyst. The C/Fe 3 C/Fe0 composite demonstrated excellent performance for both OTC and CAP removal as compared with Fe0 and biochar. Furthermore, X-ray photoelectron spectrometry, Fourier transform infrared spectrometry, high performance liquid chromatography-mass spectra and electron spin resonance analyses were conducted to elucidate the adsorption and degradation mechanisms. The adsorption of OTC and CAP was mainly dominated by H bonds and the electron-acceptor-acceptor on the surface of the C/Fe 3 C/Fe0 composite, respectively. In particular, OH simultaneously induced the degradation of OTC and CAP, while 1O 2 presented the selective oxidation to OTC. More specifically, the degradation of OTC over C/Fe 3 C/Fe0 was stronger and faster than that of CAP, leading to 65.84% and 16.84% of removal efficiency for OTC and CAP, respectively. Furthermore, C/Fe 3 C/Fe0 exhibited superior reusability and stability after regeneration, but regenerated Fe0 almost lost its reactivity. Therefore, the efficiency in situ generation of 1O 2 using C/Fe 3 C/Fe0 would shed new light on the selective oxidation of aqueous organic compounds. [ABSTRACT FROM AUTHOR]

• The methoxy content of biochar was increased by NaOH impregnation. • Precipitation, acid-base action, complexation dominated the adsorption mechanism. • The adsorption capacity could be enhanced 4.6 times. • Salt-sealing oxygen pyrolysis of biomass was performed using mixed salt. Activated biochar (A-BC550) that was prepared by salt-sealing pyrolysis (at 550 °C) and coupled with NaOH treatment was used to remove cadmium (II) from an aqueous solution. The FTIR spectroscopy and XPS analysis showed that the content of carboxyl and methoxy (CH 3 O) groups was increased by the NaOH impregnation that occurred before pyrolysis. The complexation and precipitation that occurred played a leading role in the subsequent adsorption. Adsorption occurred on the surface of the biochar, and the adsorption equilibrium was achieved in approximately 10 min of reaction following the pseudo second-order kinetic model and the Redlich-Peterson isotherm model. The maximum adsorption capacity of A-BC550 was determined by the Sips isotherm model to be 216.2 mg g−1 at pH = 7, which was 4.6 times that of the unmodified biochar without the NaOH treatment (47.13 mg g−1). Thermodynamic parameters showed the increase of adsorption temperature was conducive to the adsorption process. This work provides a low-cost and environmentally friendly method to pyrolyze biochar. The A-BC550 is a favorable material for treating heavy metal-contaminated wastewater. [ABSTRACT FROM AUTHOR]