Activated biochar with iron-loading and its application in removing Cr (VI) from aqueous solution

Insights into the Mechanism of Efficient Cr(VI) Removal from Aqueous Solution by Iron-Rich Wheat Straw Hydrochar: Coupling DFT Calculation with Experiments

Agricultural solid waste has become one of the raw materials for hydrothermal carbon production, promoting resource utilization. This study synthesized two types of ball-milling carbons (Fe-MHBC vs MHBC) with and without FeCl3 modification using wheat straw hydrochars. Cr(VI) adsorption on these two types of ball-milling carbons was investigated. According to Langmuir's maximum adsorption capacity analysis, Fe-MHBC had a capacity of 116.29 mg g-1. The thermodynamic analysis based on isothermal adsorption reveals the spontaneous process of the reaction between the two materials. The adsorption of Cr(VI) on Fe-MHBC exhibited excellent agreement with the pseudo-second-order kinetics model. Furthermore, X-ray photoelectron spectroscopy analysis showed that Fe(II) in the material reduced Cr(VI) when it participated in the reaction. The acidic conditions facilitate the elimination of Cr(VI). The Fe-MHBC has a higher zeta potential, which enhances the electrostatic attraction of Cr(VI) particles. Even with a starting pH of 10, the removal rate can be consistently maintained at over 64%. The adsorption of Cr(VI) was inhibited by various anions and higher ion concentrations. Density functional theory demonstrates that the presence of Fe enhances the adsorption capacity and electron transfer flux of Cr(VI). Fe-MHBC effectively eliminates Cr(VI) by the process of electrostatic adsorption, redox, and complexation reactions. This study demonstrated that hydrochar materials modified by FeCl3 through a ball-milling process show considerable potential as effective adsorbents in the treatment of Cr(VI) pollution, offering a viable and environmentally friendly solution for mitigating this prevalent environmental issue.

Fe doping enhanced Cr(VI) adsorption efficiency of cerium-based adsorbents: Adsorption behaviors and inner removal mechanisms

Cerium-based adsorbents possessed unique advantages of valence variability and abundant oxygen vacancies in hexavalent chromium (Cr(VI)) adsorption, but high cost and unstable properties restricted their application in Cr(VI) contained wastewater treatment. Herein, a series of bimetallic adsorbents with different cerium/iron ratios (CeFe@C) were prepared by adding inexpensive Fe into Ce-based adsorbents (Ce@C), and the effect of Fe doping on adsorption properties of Ce@C for Cr(VI) was investigated thoroughly. Compared with pristine Ce@C, CeFe@C exhibited excellent removal performance for Cr(VI), and the improved maximum adsorption capacity reached 75.11 mg/g at 25℃. Benefiting from Fe doping, CeFe@C had good regeneration property, with only 25 % decrease after five adsorption-desorption cycles. Contents of trivalent cerium (Ce(III)) and oxygen vacancies (Ov) in bimetallic adsorbents were positively correlated with divalent iron (Fe(II)) doping, indicating that the formation of Ce(III) and surface defects on Ce@C could be effectively regulated by Fe doping. Density functional theory (DFT) calculation results further proved that the doped Fe enhanced the electron transfer effectively and lowered the energy barriers of Cr(VI) adsorption onto Ce@C surface, strengthening the reduction and complexation to Cr(VI). This study provides new insights for improving the Cr(VI) removal performance by modified Ce-based adsorbents, and further promotes the utilization potentiality of low-cost and low-toxicity Ce-based adsorbents in Cr(VI)-containing wastewater treatment.

A promising approach for the removal of hexavalent and trivalent chromium from aqueous solution using low-cost biomaterial

Heavy metal pollution is an enduring environmental challenge that calls for sustainable and eco-friendly solutions. One promising approach is to harness discarded plant biomass as a highly efficient environmental friendly adsorbents. In this context, a noteworthy study has spotlighted the employment of Euryale ferox Salisbury seed coat (E.feroxSC) for the exclusion of trivalent and hexavalent chromium ions. This study aims to transform discarded plant residue into a novel, environmentally friendly, and cost-effective alternative adsorbent, offering a compelling alternative to more expensive adsorption methods. By repurposing natural materials, we can contribute to mitigating heavy-metal pollution while promoting sustainable and economically viable solutions in environmental remediation. The effect of different parameters, i.e., chromium ions' initial concentration (5-25 mg L-1), solution pH (2-7), adsorbent dosage (0.2-2.4 g L-1), contact time (20-240 min), and temperature (298-313 K), were investigated. E.feroxSC proved highly effective, achieving 96.5% removal of Cr(III) ions at pH 6 and 97.7% removal of Cr(VI) ions at pH 2, with a maximum biosorption capacity of 18.33 mg/g for Cr(III) and 13.64 mg/g for Cr(VI), making it a promising, eco-friendly adsorbent for tackling heavy-metal pollution. The adsorption process followed the pseudo-second-order kinetic model, aligning well with the Langmuir isotherm, exhibited favorable thermodynamics, and was characterized as feasible, spontaneous, and endothermic with physisorption mechanisms. The investigation revealed that E.feroxSC effectively adsorbed Cr(VI) which could be rejuvenated in a basic solution with minimal depletion in its adsorption capacity. Conversely, E.feroxSC's adsorption of Cr(III) demanded rejuvenation in an acidic milieu, exhibiting comparatively less efficient restoration.

Changes of MRGs and ARGs in Acinetobacter sp. SL-1 used for treatment of Cr(VI)-contaminated wastewater with waste molasses as carbon source

Antibiotic resistance genes (ARGs) may be synergistic selected during bio-treatment of chromium-containing wastewater and causing environmental risks through horizontal transfer. This research explored the impact of self-screening bacterium Acinetobacter sp. SL-1 on the treatment of chromium-containing wastewater under varying environmental conditions. The findings indicated that the optimal Cr(VI) removal conditions were an anaerobic environment, 30 °C temperature, 5 g/L waste molasses, 100 mg/L Cr(VI), pH = 7, and a reaction time of 168 h. Under these conditions, the removal of Cr(VI) reached 99.10 %, however, it also developed cross-resistance to tetracycline, gentamicin, clarithromycin, ofloxacin following exposure to Cr(VI). When decrease Cr(VI) concentration to 50 mg/L at pH of 9 with waste molasses as carbon source, the expression of ARGs was down regulated, which decreased the horizontal transfer possibility of ARGs and minimized the potential environmental pollution risk caused by ARGs. The study ultimately emphasized that the treatment of chromium-containing wastewater with waste molasses in conjunction with SL-1 not only effectively eliminates hexavalent chromium but also mitigates the risk of environmental pollution.

Removal of Cr(VI) from aqueous solution using ball mill modified biochar: multivariate modeling, optimization and experimental study

Chromium (Cr(VI)) pollution has attracted wide attention due to its high toxicity and carcinogenicity. Modified biochar has been widely used in the removal of Cr(VI) in water as an efficient and green adsorbent. However, the existing biochar prepared by chemical modification is usually complicated in process, high in cost, and has secondary pollution, which limits its application. It is urgent to explore modified biochar with simple process, low cost and environmental friendliness. Therefore, ball milling wheat straw biochar (BM-WB) was prepared by ball milling technology in this paper. The adsorption characteristics and mechanism of Cr(VI) removal by BM-WB were analyzed by functional group characterization, adsorption model and response surface method. The results showed that ball milling effectively reduced the particle size of biochar, increased the specific surface area, and more importantly, enhanced the content of oxygen-containing functional groups on the surface of biochar. After ball milling, the adsorption capacity of Cr(VI) increased by 3.5-9.1 times, and the adsorption capacity reached 52.21 mg/g. The adsorption behavior of Cr(VI) follows the pseudo-second-order kinetics and Langmuir isotherm adsorption model rate. Moreover, the Cr(VI) adsorption process of BM-WB is endothermic and spontaneous. Under the optimized conditions of pH 2, temperature 45 °C, and adsorbent dosage 0.1 g, the removal rate of Cr(VI) in the solution can reach 100%. The mechanism of Cr(VI) adsorption by BM-WB is mainly based on electrostatic attraction, redox and complexation. Therefore, ball milled biochar is a cheap, simple and efficient Cr(VI) removal material, which has a good application prospect in the field of remediation of Cr(VI) pollution in water.

Low-temperature biochar production from torrefaction for wastewater treatment: A review

Biochar, a carbon-rich and por ous material derived from waste biomass resources, has demonstrated tremendous potential in wastewater treatment. Torrefaction technology offers a favorable low-temperature biochar production method, and torrefied biochar can be used not only as a solid biofuel but also as a pollutant adsorbent. This review compares torrefaction technology with other thermochemical processes and discusses recent advancements in torrefaction techniques. Additionally, the applications of torrefied biochar in wastewater treatment (dyes, oil spills, heavy metals, and emerging pollutants) are comprehensively explored. Many studies have shown that high productivity, high survival of oxygen-containing functional groups, low temperature, and low energy consumption of dried biochar production make it attractive as an adsorbent for wastewater treatment. Moreover, used biochar's treatment, reuse, and safe disposal are introduced, providing valuable insights and contributions to developing sustainable environmental remediation strategies by biochar.

Adsorption properties and mechanism of suaeda biochar and modified materials for tetracycline

Adsorption was an available way to eliminate Tetracycline (TC) from waste water. Suaeda biochar (800SBC) and iron modified biochar (Fe-800SBC) were prepared using pyrolysis under oxygen-limiting conditions. BET and SEM showed that the surface of Fe-800SBC was rougher, and the specific surface area (SBET) was 7 times that of 800SBC. There existed pore filling, ion exchange, metal ion complexation, hydrogen bonds and cation-π interaction mechanism. Both 800SBC and Fe-800SBC conformed to quasi-second-order kinetics model, belonged to chemisorption. Fe-800SBC conformed to Elovich model too. The adsorption process of 800SBC conformed to Freundlich and Sips L-F models, Fe-800SBC conformed to the Sips L-F and Temkin models, identifying the presence of physical and chemical adsorption during adsorption. Response surface method (RSM) was used to optimize important process parameters. The quadratic model was sufficient to predict TC removal response in the range of studied parameters.

A review on chromium health hazards and molecular mechanism of chromium bioremediation

Living beings have been devastated by environmental pollution, which has reached its peak. The disastrous pollution of the environment is in large part due to industrial wastes containing toxic pollutants. The widespread use of chromium (Cr (III)/Cr (VI)) in industries, especially tanneries, makes it one of the most dangerous environmental pollutants. Chromium pollution is widespread due to ineffective treatment methods. Bioremediation of chromium (Cr) using bacteria is very thoughtful due to its eco-friendly and cost-effective outcome. In order to counter chromium toxicity, bacteria have numerous mechanisms, such as the ability to absorb, reduce, efflux, or accumulate the metal. In this review article, we focused on chromium toxicity on human and environmental health as well as its bioremediation mechanism.

Preparation of biochar-based surface molecularly imprinted polymers and evaluation of their selective adsorption and removal of carbaryl from rice and corn

The residue of carbaryl in food is a threat to human health. In this study, activated soybean shell biochar (A-SBC) was used as a carrier, methacrylic acid (MAA) was used as a functional monomer, and carbaryl was used as a template molecule to synthesize the activated biochar surface molecularly imprinted polymer (A-SBC@MIP). The synthesized A-SBC@MIP was characterized by SEM, FT-IR, XRD and XPS techniques, and then applied as adsorbent for carbaryl removal. The adsorption capacity of A-SBC@MIP for carbaryl was 8.6 mg‧g-1 and the imprinting factor was 1.49 at the optimum ionic strength and pH. The kinetic and isothermal data indicated that it had fast mass transfer rate and high binding capacity(Qmax=47.9 mg‧g-1). A-SBC@MIP showed good regenerative properties and the adsorption of carbaryl was excellent in its structural analogues. A solid-phase extraction (SPE) column composed of A-SBC@MIP was developed for the detection of rice and corn under optimized conditions, with recoveries of 93-101% for the spiked carbaryl. The limit of detection (LOD) of the method was 3.6 μg‧kg-1 with good linearity (R2=0.994) in the range of 0.01-5.00 mg‧L-1. The results show that the developed MIPs-SPE can enrich carbaryl from food samples as a specific and cost-effective method.

Fe-N-Doped Conjugated Organic Polymer Efficiently Enhanced the Removal Rate of Cr(VI) from Water

A Fe-N conjugated organic polymer (SMP-Fr-Py) was prepared from ferrocene and pyrrole using a Scholl coupling reaction, which significantly improved the performance of Cr(VI) removal compared to the polymer (HCP-Fr-Py) prepared by adding the cross-linker formaldehyde dimethyl acetal (FDA). The results showed that at a pH of 2 and at 25 °C, the removal of Cr(VI) reached 90% for SMP-Fr-Py and only 58% for HCP-Fr-Py after 20 min of reaction. Subsequently, 99% and 78% were achieved after 120 min of reaction, respectively. The test results showed that the removal reaction followed a pseudo-second-order kinetic model. The removal efficiency decreased with increasing solution pH and initial Cr(VI) concentration, but increased with increasing SMP-Fr-Py dosage, reaching three cycles. The characterization of the reaction complexes and measurements of Cr species conversion revealed the near absence of Cr(VI) species in the solution. Approximately 38% of Cr(VI) was found to be adsorbed on the material surface, with another fraction present in solution (24%) and on the material surface (38%) in the form of Cr(III). The overall study showed that the direct connection of ferrocene and pyrrole in SMP-Fr-Py through C-C bonding increased the conjugated structure of the polymer backbone, which facilitated electron transfer and transport. Furthermore, the Fe-N elements worked synergistically with each other more easily, which improved the removal performance of Cr(VI) and provided a reference for the subsequent work.

Review on Rice Husk Biochar as an Adsorbent for Soil and Water Remediation

Rice husk biochar (RHB) is a low-cost and renewable resource that has been found to be highly effective for the remediation of water and soil environments. Its yield, structure, composition, and physicochemical properties can be modified by changing the parameters of the preparation process, such as the heating rate, pyrolysis temperature, and carrier gas flow rate. Additionally, its specific surface area and functional groups can be modified through physical, chemical, and biological means. Compared to biochar from other feedstocks, RHB performs poorly in solutions with coexisting metal, but can be modified for improved adsorption. In contaminated soils, RHB has been found to be effective in adsorbing heavy metals and organic matter, as well as reducing pollutant availability and enhancing crop growth by regulating soil properties and releasing beneficial elements. However, its effectiveness in complex environments remains uncertain, and further research is needed to fully understand its mechanisms and effectiveness in environmental remediation.

Adsorption of Cr(VI) by NaOH-modified microporous activated carbons derived from the wastes of Amaranthus retroflexus, Magnolia soulangeana, and Tanacetum Vulgar L.: mechanism, isotherms, and kinetic studies

The study was designed to synthesize microporous activated carbons from the wastes of three medicinal herbs by NaOH as an activator followed by pyrolysis. The prepared microporous activated carbons R. Weed (Amaranthus retroflexus Redroot pigweed modified with NaOH), S. Bod Magnolia soulangeana Soul-Bod treated with NaOH) and S. TY (Tanacetum Vulgar L. (Tansy) treated with NaOH) were deployed for dangerous Cr(VI) ion remediation from the aquatic system. The synthesized modified biosorbents were described by FT-IR, SEM, EDAX, and BET. Furthermore, it was found that biosorbent made from R. Weed seems to have a surface area of 588.155 m²/g and micropore volume of 0.331Cm³/g whereas biosorbent made from S. Bod and S. TY does have a surface area of 489.613 and 445.615 m²/g respectively. The effects of several variables such as pH, temperature, and contact time were explored. The kinetic studies were accomplished and it was noticed that equilibrium was confirmed at 6 min for R. Weed while at 8 and 10 min for S. Bod and S. TY respectively. The pertinence of different adsorption isotherms like Langmuir, Freundlich, and Temkin was explored. The optimum adsorption capacity for each adsorbent material in respect of monolayer coverage (Q_max) was calculated. The Q_max of Redroot pigweed (R. Weed), Soul-Bod (S. Bod), and Tansy (S. TY) biosorbents were 326.62, 181.69, and 108.14 mg/g respectively. The adsorption kinetics was described using pseudo-first-order and pseudo-second-order equations. Furthermore, it was found that each adsorbent material followed the pseudo-second-order kinetics which affirmed the chemosorption nature of adsorption. The thermodynamic variables that include ΔG, ΔH, and ΔS were determined for each adsorbent material. Moreover, the manufactured R. Weed biosorbent seems to have high recyclability. It will remediate Cr(VI) ions with a maximum remediation efficiency of up to 81% during six cycles of regeneration.

Synthesis, Adsorption Isotherm and Kinetic Study of Alkaline- Treated Zeolite/Chitosan/Fe3+ Composites for Nitrate Removal from Aqueous Solution-Anion and Dye Effects

In the present study, alkaline-treated zeolite/chitosan/Fe³⁺ (ZLCH-Fe) composites were prepared and analyzed using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and pH of zero point of charge (pH_zpc) to remove nitrates from water. The process was carried out using an adsorption method with a varied initial pH, adsorbent dosage, initial nitrate concentration and contact time. The pH_zpc demonstrated that the ZLCH-Fe surface had a positive charge between 2 and 10, making it easier to capture the negative charge of nitrate. However, the optimal pH value is 7. After 270 min, the maximum adsorption capacity and percent removal reached 498 mg/g and 99.64%, respectively. Freundlich and pseudo-second-order were fitted to the adsorption isotherm and kinetic models, respectively. An evaluation was conducted on the effects of anions-SO₄^2- and PO₄^3--and dyes-methylene blue (MB) and acid red 88 (AR88)-upon nitrate removal. The results indicated that the effect of the anion could be inhibited, in contrast to dye effects. However, the optimal pH values were changed to 10 for MB and 2 for AR88, resulting in a hydrogel formation. This might be indicated by the protonation of hydroxyl and amino groups resulting from a chitosan nitrate reaction in the AR88 solution.

Biosorption of Cr (VI) by acid-modified based-waste fungal biomass from Calocybe indica fruiting bodies production

The world is going through a colossal drinking water scarcity. Unchecked discharge (even at trace levels) of Cr (VI) from industries into water bodies is a serious environmental concern. Here, we report waste fungal biomass (WFB) for the detoxification and removal of chromium ions. Biomass understudy was collected from Calocybe indica fruiting bodies. WFB was used after drying and pretreatment with two distinctive chemical methods, which improved the remediation effectiveness of Cr (VI). Light microscope and Field emission Scanning microscope (FESEM) were employed to elucidate the surface morphology of waste fungal biomass. While Fourier-Transform Infrared-Spectroscopy (FTIR) and Energy Dispersive X-Ray analysis (EDAX) were deployed to explore the mechanism of interaction between Cr (VI) anion and waste fungal biomass. X-ray Photoelectron Spectroscopy (XPS) analyses demonstrated considerable conversion of Cr (VI) into nontoxic Cr (III) species. The most favorable condition for optimum Cr (VI) remediation of 99.66% by treated waste fungal biomass (TWFB) occurred at pH 3, contact time 10 min, adsorbent dosage 3 gL^-1, Cr (VI) concentration 4 mgL^-1, stirring speed 140 rpm, and temperature 320 K, where for untreated waste fungal biomass (UWFB) the optimum of 85% remediation occurred at a contact time 15 min, and adsorbent dosage 2 gL^-1 whereas other experimental conditions remained identical as TWFB biosorbent. Pseudo-second-order kinetics (R² > 0.99) model matched the adsorption rate. And, the Freundlich isotherm model (R² > 0.99) is shown to be a better match for the experimental data. The optimum amount of Cr (VI) adsorbed by the TWFB and UWFB were 205.8 ± 10.1 and 72.85 ± 2.36 mgg^-1, respectively. Thermodynamic parameters revealed that the adsorption was spontaneous (ΔG ˂ 0), endothermic (ΔH > 0), and entropy-driven (ΔS > 0). The generated WFB adsorbent also has significant recycling potential. After five cycles of regeneration and adsorption. It can still keep up good remediation effectiveness of Cr (VI) ions to 85.5.

Iron-modified biochar-based bilayer permeable reactive barrier for Cr(VI) removal

Iron (Fe)-modified biochar (FeBC) has been developed to remove hexavalent chromium (Cr(VI)) from groundwater and is suitable for use in permeable reactive barriers (PRBs). However, Cr(VI) removal behavior and chemical processes in FeBC-based PRBs are not fully understood, and the potential for Fe release has not been addressed. In this study, three FeBC-based PRBs were assessed in column experiments for 563 days with respect to their ability to remove Cr(VI). Bilayer column filled with FeBC+limestone and BC+limestone in two separate layers (FeBC_Ca_BC) showed the best performance in terms of Cr(VI) removal with a low treatment cost. The corrosion of FeBC was mainly related to pH and Cr(VI) concentration rather than flow rate. Leached Fe was attenuated by BC and limestone and reutilized in FeBC_Ca_BC. Cr(VI) was reduced to Cr(III) and then adsorbed or precipitated on the biochars. Cr and Fe formed inner-sphere complexes and then transformed from double corner sharing to edge sharing. During the reaction, Cr penetrated from the surface to the interior of the biochars and became a more stable species. This study provides evidence of the effectiveness of a new combination of biochars for Cr(VI) removal and insights into the reaction mechanisms.

Resource utilization of rice husk biomass: Preparation of MgO flake-modified biochar for simultaneous removal of heavy metals from aqueous solution and polluted soil

In general, the remediation performance of heavy metals can be further improved by metal-oxide modified biochar. This work used MgO-modified rice husk biochar (MgO-5%@RHB-450 and MgO-5%@RHB-600) with high surface activity for simultaneous remediation and removal of heavy metals in soil and wastewater. The adsorption of MgO-5%@RHB-450/MgO-5%@RHB-600 for Cd(II), Cu(II), Zn(II) and Cr(VI) followed the pseudo-second order, with the adsorption capacities reaching 91.13/104.68, 166.68/173.22, 80.12/104.38 and 38.88/47.02 mg g^-1, respectively. The addition of 1.0% MgO-5%@RHB-450 and MgO-5%@RHB-600 could effectively decrease the CaCl₂-extractable Cd concentration (CaCl₂-Cd) by 66.2% and 70.0%, respectively. Moreover, MgO-5%@RHB-450 and MgO-5%@RHB-600 facilitated the transformation of exchangeable fractions to carbonate-bound and residual fractions, and reduced the exchangeable fractions by 8.1% and 9.6%, respectively. The mechanisms for the removal of heavy metals from wastewater by MgO-5%@RHB-450 and MgO-5%@RHB-600 mainly included complexation, ion exchange and precipitation, and the immobilization mechanisms in soil may be precipitation, complexation and pore filling. In general, this study provides high-efficiency functional materials for the remediation of heavy metal pollution.

Improved Electron Efficiency of Zero-Valent Iron towards Cr(VI) Reduction after Sequestering in Al2O3 Microspheres

Zero-valent iron (ZVI) is widely used for groundwater remediation, but suffers from high electron consumption because of its free contact with non-target substrates such as O₂. Here, ZVI-ALOX particles were prepared via in situ NaBH₄ aqueous-phase reduction of ferrous ions (Fe²⁺) preabsorbed into Al₂O₃ microspheres. The electron efficiency (EE) and long-term performance of the material were improved by sequestering ZVI in the interspace of the Al₂O₃ microspheres (ZVI-ALOX). During long-term (350 days) continuous flow, Cr(VI) was removed to below the detection limit for over 23 days. Based on the high reactivity of ZVI towards Cr(VI), the EE of ZVI-ALOX was evaluated by measuring its Cr(VI) removal efficiency at neutral pH and comparing it with that of ZVI. The results showed that the EE of ZVI-ALOX during long-term continuous flow could reach 39.1%, which was much higher than that of ZVI (8.68%). The long-term continuous flow results also demonstrated that treatment of the influent solution achieved higher EE values than in the batch mode, where the presence of dissolved oxygen reduced EE values. At lower pollutant concentrations, the sequestering of ZVI was beneficial to its performance and long-term utility. In addition, measurement of the acute toxicity of treated column effluent using the indicator organism Photobacterium phosphoreum T₃ showed that ZVI-ALOX could reduce the toxicity of 5 mg/L Cr(VI) solution by ~70% in 350 d. The results from this study provide a basis for the development of permeable reactive barriers for groundwater remediation based on sequestered ZVI.

Insights into Cr(VI) removal mechanism in water by facile one-step pyrolysis prepared coal gangue-biochar composite

The acceleration of industrialization has increased the discharge of chromium-containing wastewater, posing serious threat to the eco-environment and human health. To remove Cr(VI) in wastewater and improve resource utilization of solid waste, coal gangue and rape straw were initially used to prepare coal gangue-rape straw biochar (CG-RS) composite. The effects of pyrolysis temperatures, solution pH, coexisting ions of Cr(VI) adsorption were investigated. Different adsorption models combined with site energy analysis were used to explore the adsorption behaviors and mechanisms. The results showed higher pyrolysis temperature (600 °C) prepared CG-RS had a larger adsorption capacity (9.2 mg/g) for Cr(VI) (pH = 5.0). Analysis of XPS indicated that CG-RS successfully loaded with Fe-O and Al-O functional groups, which mainly participated in the reduction of Cr(VI). Site energy analysis further proved that reduction and surface complexation were the main adsorption mechanisms. This study shows an effective removal of Cr(VI) by CG-RS, providing a new way for resource utilization of solid waste.

Synergistic remediation of Cr(VI) contaminated soil by iron-loaded activated carbon in two-chamber microbial fuel cells

The soil remediation by microbial fuel cells (MFCs) is still challenging due to the high mass transfer resistance limiting the overall performance. To improve the remediation of Cr(VI) contaminated soil, iron-loaded activated carbon (AC-Fe) particles were synthesized and spiked into soil to establish an enhanced MFC system. The AC-Fe particles are porous and conductive with a high specific surface area of 1166.5 m²/g. The addition of AC-Fe particles could reduce the overall resistance from 4269.2 Ω to 303.1 Ω with the optimum dosage of 0.3%. The maximum power generation of MFC was 11.5 mW/m², and Cr(VI) removal efficiency reached as high as 84.2 ± 1.2% in 24 h. It was found that AC-Fe particles were able to simultaneously adsorb and reduce Cr(VI) to Cr(III); in the meantime, Fe(II) loaded on the AC-Fe was oxidized to Fe(III). Spiking more AC-Fe particles in the contaminated soil had a negative effect. It was probably because that AC-Fe particles working as the third electrodes would hinder the overall ion electromigration and decrease Cr(VI) reduction at the cathode. The enhanced system which coupled MFC and AC-Fe showed a synergistic removal of Cr(VI), with the maximum improvement of 22.1% compared to the sum of Cr(VI) removals by the individual ones.

Remediation of Chromium (VI) from Groundwater by Metal-Based Biochar under Anaerobic Conditions

Iron salt-modified biochar has been widely used to remove Cr(VI) pollution due to the combination of the generated iron oxides and biochar, which can bring positive charge and rich redox activity. However, there are few comprehensive studies on the methods of modifying biochar with different iron salts. In this study, two iron salt (FeCl3 and Fe(NO3)3) modification methods were used to prepare two Fe-modified biochar materials for removing Cr(VI) in simulated groundwater environment. It was revealed by systematic characterization that FeCl3@BC prepared via the FeCl3 modification method, has larger pore size, higher zeta potential and iron oxide content, and has higher Cr(VI) adsorption-reduction performance efficiency as compared to Fe(NO3)3@BC prepared via Fe(NO3)3 modification method. Combined with XRD and XPS analyses, Fe3O4 is the key active component for the reduction of Cr(VI) to Cr(III). The experimental results have shown that acidic conditions promoted Cr(VI) removal, while competing ions (SO42− and PO43−) inhibited Cr(VI) removal by FeCl3@BC. The Elovich model and intra-particle diffusion model of FeCl3@BC can describe the adsorption behavior of Cr(VI) well, indicating that both the high activation energy adsorption process and intra-particle diffusion control the removal process of Cr(VI). The Freundlich model (R2 > 0.999) indicated that there were unevenly distributed chemisorptions centers on the FeCl3@BC surface. Stability experiments exposed that FeCl3@BC was stable under neutral, acidic, and alkaline conditions. Furthermore, the main mechanisms of FeCl3@BC removal of Cr(VI) include electrostatic adsorption, chemical reduction, ion exchange, and co-precipitation. In conclusion, our findings provide a new insight for the selection of iron salt-modified biochar methods, and will also be beneficial for the preparation of more efficient Fe-modified biochars in the future.

A systematic review on adsorptive removal of hexavalent chromium from aqueous solutions: Recent advances

The contamination of natural resources by hexavalent chromium (Cr(VI)) originating from natural and anthropogenic activities is a serious environmental concern. Although many articles on chromium remediation have been published, a comprehensive understanding of the mechanisms involved in remediation with different sorbents is not yet available. In this systematic review, the performance and applicability of several adsorptive materials for Cr(VI) removal from aqueous media are discussed, along with a detailed analysis of the mechanisms involved. Statistical analysis is applied to compare the efficacies of different adsorbents, while a similar approach is used to determine the effects of sorbent properties and experimental conditions on the adsorption capacity. A detailed analysis of the factors involved in fixed-bed column studies is also presented. A suitable desorption approach to the regeneration of the spent adsorbent and its adsorption performance in reuse is also examined. Among the different sorbents, nanoparticles and mineral-doped biochar were found to be the most effective sorbents, while the adsorption was higher at low pH (~4.0) than that at intermediate pH (6-8). Contrary to our expectation, adsorption was high for sorbents with low specific surface areas, suggesting that the adsorption of Cr(VI) is largely influenced by the chemical properties of the sorbents. The optimum adsorption in fixed-bed column systems is obtained at a lower Cr(VI) ion concentration, a lower influent flow rate, and a higher bed height. Since most of the studies reviewed herein were merely experimental and utilized ideal conditions with the presence of a single contaminant, i.e. Cr(VI) in water, further studies on adsorption dynamics with the presence of other interfering ions are suggested. This review is promising for the further development of Cr(VI) removal strategies and closes the research gaps pertaining to their challenges.

Facile Synthesis of Magnetic Biochar Derived from Burley Tobacco Stems towards Enhanced Cr (VI) Removal: Performance and Mechanism

In this study, ferric-loaded magnetic burley tobacco stem biochar (MBTS) was synthesized via pyrolysis to improve the removal of Cr(VI). The results showed that MBTS had an adsorption capacity of 54.92 mg Cr(VI)/g, which was about 14 times higher than raw burley tobacco stem biochar (i.e., 3.84 mg/g). According to the findings obtained, a three-step mechanism of Cr(VI) removal by MBTS was further put forward, i.e., (1) Cr(VI) exchanged with hydroxyl groups on MBTS, (2) the reduction in Cr(VI) to Cr(III) mediated by oxygen-containing groups, and (3) the chelation of produced Cr(III) with the amino groups on MBTS. FTIR spectra further revealed that C-N, C-H, and C=C groups played an important role in Cr(VI) removal. Furthermore, the adsorption equilibrium and kinetics of Cr(VI) on MBTS could better be described by the Langmuir equation and pseudo-second-order rate equation. This study clearly demonstrated that ferric-loaded biochar derived from burley tobacco stems could serve as a cost-effective magnetic adsorbent for the high-efficiency removal of soluble Cr(VI) from wastewater. Tobacco stem-adsorbed Cr(VI) realized a green path for treating waste by waste.

Obtention of biochar-Ca nanoparticles using Citrus tangerina׃ A morphological, surface and study remotion of Aflatoxin AFB1

This work presents the formation of biochar with calcium nanoparticles (NPsCa) in function of pyrolysis time (C10, C30, C60, C120 and C180 min) using the Citrus tangerina peel and their evaluation in the remotion of Aflatoxin B1 (AFB1) in aqueous phase. Firstly, the Citrus tangerina was studied by Thermogravimetric analysis to determine the optimal temperature (TGA), obtaining a result of 600 °C. The biochar (NPsCa) were characterized by Scanning Electronic Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), as well as surface properties including the identification of functional groups by Fourier Transform Infrared Spectrometry (FTIR), and energetic states through the X-Ray Photoelectron Spectroscopy (XPS). The adsorption studies were carried out on the different materials and later, the experimental data was adjusted to different mathematical models, obtaining the best fit of the kinetic data to the Ho-McKay model, whilst the adsorption isotherms were adjusted to the model of Langmuir, which indicates that the Aflatoxin B1 adsorption process is carried out through a monolayer chemisorption process with maximum sorption capacities (qm) ranging between 15.72 and 63.22 μg g^-1 with the 180th minute being the adequate time to obtain the carbon with the best surface properties and the best adsorption capacity. Additionally, it was observed that each material can be reused up to five times in accordance with the results from the reuse cycles.

Biomass-derived carbon-based and silica-based materials for catalytic and adsorptive applications- An update since 2010

Biomass, which defined as plant- or animal-based materials, is intriguing tremendous scientific attentions due to its renewable attribute in serving energy security. Amongst, the plant-based biomasses, particularly those that co-generated in the agriculture activities, are commonly regarded as fuel for burning, which overlooked their hidden potentials for high-end applications. Organically, the plant-based biomass constitutes of lignocellulose components, which can be served as promising precursors for functionalized carbon materials. Meanwhile, its inorganic counterpart made up of various minerals, with Si being the most concerned one. With the advancement of biomass technologies and material synthesis in recent years, numerous attempts were endeavoured to obtain valorised products from biomass. Particularly, syntheses of catalytic and adsorptive materials are actively researched in the field of biomass reutilization. Herein, our work systematically summarized the advancements of biomass-materials for these applications in recent 10 years (2010-2020), with a special focus on the carbon-based and Si-based catalytic/adsorptive materials. Significantly, the deriving steps, inclusive of both pre-treatment and post-treatment of such materials, are incorporated in the discussion, alongside with their significances revealed too. The performance of the as-obtained materials in the respective application is systematically correlated to their physicochemical properties, hence providing valuable insights to the readers. Challenges and promising directions to be explored are raised too at the end of the review, aiming to advocate better-usage of biomass while offering great opportunities to sustain catalysis and adsorption in the industrial scale.

Green Hydrogel-Biochar Composite for Enhanced Adsorption of Uranium

Uranium is the backbone of the nuclear fuel used for energy production but is still a hazardous environmental contaminant; thus, its removal and recovery are important for energy security and environmental protection. So far, the development of biocompatible, efficient, economical, and reusable adsorbents for uranium is still a challenge. In this work, a new orange peel biochar-based hydrogel composite was prepared by graft polymerization using guar gum and acrylamide. The composite's structural, morphological, and thermal characteristics were investigated via Fourier transform infrared (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. The composite's water absorption properties were investigated in different media. The performance of the prepared composite in adsorbing uranium (VI) ions from aqueous media was systematically investigated under varying conditions including solution's acidity and temperature, composite dose, contact time, and starting amount of uranium. The adsorption efficiency increased with solution pH from 2 to 5.5 and composite dose from 15 to 50 mg. The adsorption kinetics, isotherms, and thermodynamics parameters were analyzed to get insights into the process's feasibility and viability. The equilibrium data were better described through a pseudo-second-order mechanism and a Langmuir isotherm model, indicating a homogeneous composite surface with the maximum uranium (VI) adsorption capacity of 263.2 mg/g. The calculated thermodynamic parameters suggested that a spontaneous and endothermic process prevailed. Interference studies showed high selectivity toward uranium (VI) against other competing cations. Desorption and recyclability studies indicated the good recycling performance of the prepared composite. The adsorption mechanism was discussed in view of the kinetics and thermodynamics data. Based on the results, the prepared hydrogel composite can be applied as a promising, cost-effective, eco-friendly, and efficient material for uranium (VI) decontamination.

An efficient, economical, and easy mass production biochar supported zero-valent iron composite derived from direct-reduction natural goethite for Cu(II) and Cr(VI) remove

In this study, a novel biochar-supported zero-valent iron (ZVI) composite was synthesised by a one-pot co-pyrolysis reduction method, and was used to remove Cu(II) and Cr(VI). The raw materials for the composite were derived from natural bagasse/straw and goethite. Scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry (TG), and Brunauer-Emmett-Teller (BET) analysis were used to characterise the biochar and biochar-supported ZVI composites. Batch removal experiments on the effects of the initial pH and citric acid concentrations were performed as well as kinetic studies and isotherm experiments. The composite materials showed better Cu(II) and Cr(VI) removal performance than single biochar and mineral. The removal of Cu(II) and Cr(VI) is pH-dependent, and proceeds via heterogeneous multilayer chemisorption. Electrochemical analysis revealed that straw biochar-supported ZVI composite exhibited greater electrical conductivity and electron transfer rate than pure biochar and ZVI. FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS) elucidated the uptake mechanism, showing that Cu(II) and Cr(VI) were easily adsorbed onto the biochar surface and were then reduced by ZVI. These results indicate that biochar-supported ZVI composite is effective for heavy metal remediation, which is economical, environment-friendly, and suitable for mass production.

Designing of a nanoscale zerovalent iron@fly ash composite as efficient and sustainable adsorbents for hexavalent chromium (Cr(VI)) from water

The present study encompasses a unique concept involving the formation of core-shell particles with surface-activated fly ash (FA) as core and nanoscale zerovalent iron (nZVI) particles as shell, which not only imparts high adsorption efficiency for Cr(VI) but also contributes to fruitful utilization of FA while overcoming the drawbacks associated with ZVI nanoparticles (aggregation, rapid oxidation and less durability). The otherwise inert surface of FA has been modified and activated to achieve a uniform and stable layer of nZVI over FA. The functionalized particles were studied using FE-SEM/EDAX, HR-TEM, XRD and FT-IR studies for its physical, functional and morphological characteristics. The results indicate the strong adsorption ability of nZVI@FA particles, with 100% removal efficiency within 10 min at low initial concentrations of Cr(VI), which is appreciably higher than that of pure fly ash (26%) after 60 min of reaction. Besides, the so-formed structure of composite aids to improve its life, as the synthesized nZVI@FA particles could be efficiently regenerated and reused up to 5 subsequent adsorption-desorption cycles, which is in contrast with the ability of fly ash considering its low desorption potential. Hence, the composite material proves to be an effective and sustainable alternative for treatment of a waste using a waste.

Single and Competitive Adsorption Behaviors of Cu2+, Pb2+ and Zn2+ on the Biochar and Magnetic Biochar of Pomelo Peel in Aqueous Solution

As an environment-friendly material, biochar has been used to remove heavy metals from wastewater, and the development of cost-effective biochar has been an emerging trend. However, limited studies consider the competitive adsorption of co-existing metals and the separation efficiency of absorbent and solution after adsorption. In this study, pomelo peel was used to prepare biochar (BC) and magnetic biochar (MBC) at different temperatures. Then, the physicochemical properties of the biochars were characterized and the adsorption characteristics of Cu2+, Pb2+, and Zn2+ on the biochars in single, binary, and ternary metal systems were investigated. The results showed that both pyrolysis temperature and magnetization could affect the adsorption capacity of biochar. The adsorption kinetic and thermodynamic processes could be well described by the pseudo-second-order kinetic model and Langmuir model. The adsorption isotherm types of Pb2+ and Zn2+ changed in the binary metal condition. The competitive adsorption order of three heavy metal ions in ternary metal adsorption was Pb2+ > Cu2+ > Zn2+. The MBC of 500 °C showed a good adsorption capacity to Pb2+ in the co-existing environment, and the maximum adsorption capacity was 48.74 mmol g−1. This study also provided technical support for the utilization of pomelo peel and the engineering application of biochar.

Study on detoxification and removal mechanisms of hexavalent chromium by microorganisms

Extensive industrial activities have led to an increase of the content of chromium in the environment, which causes serious pollution to the surrounding water, soil and atmosphere. The enrichment of chromium in the environment through the food chain ultimately affects human health. Therefore, the remediation of chromium pollution is crucial to development of human society. A lot of scholars have paid attention to bioremediation technology owing to its environmentally friendly and low-cost. Previous reviews mostly involved pure culture of microorganisms and rarely discussed the optimization of bioreduction conditions. To make up for these shortcomings, we not only introduced in detail the conditions that affect microbial reduction but also innovatively introduced consortium which may be the cornerstone for future treatment of complex field environments. The aim of this study is to summary chromium toxicity, factors affecting microbial remediation, and methods for enhancing bioremediation. However, the actual application of bioremediation technology is still facing a major challenge. This study also put forward the current research problems and proposed future research directions, providing theoretical guidance and scientific basis for the application of bioremediation technology.

Magnetite Functionalized Nigella Sativa Seeds for the Uptake of Chromium(VI) and Lead(II) Ions from Synthetic Wastewater

The aim of the present study was to utilise pristine and magnetite-sucrose functionalized Nigella Sativa seeds as the adsorbents for the uptake of chromium(VI) and lead(II) ions from synthetic wastewater. Prestine Nigella Sativa seeds were labelled (PNS) and magnetite-sucrose functionalized Nigella Sativa seeds (FNS). The PNS and FNS composites were characterized by Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). The FTIR analysis of both adsorbents revealed the presence of vibrations assigned to 1749 and 1739 cm-1 (-C=O) for ketonic group for both adsorbents. The amide (-NH) peak was observed at 1533 and 1527 cm-1 on FNS and PNS composites, respectively, whilst the carboxyl group (-COOH) were observed at 1408 cm-1 on both adsorbents. The XRD results of FNS and PNS composites showed a combination of spinel structure and$y$-Fe2O3 phase confirming the formation of iron oxide. The influence of operational conditions such as initial concentration, temperature, pH, and contact time was determined in batch adsorption system. The kinetic data of Cr(VI) and Pb(II) ions on both adsorbents was described by pseudo-first-order (PFO) model which suggested physisorption process. The sorption rate of Cr(VI) ions was quicker, it attained equilibrium in 20 min, and the rate of Pb(II) ions was slow in 90 min. Freundlich isotherm described the mechanism of Pb(II) ions adsorption on PNS and FNS composites. Langmuir best fitted the uptake of Cr(VI) ions on PNS and FNS. The results for both adsorbents showed that the removal uptake of Pb(II) ions increased when the initial concentration was increased; however, Cr(VI) uptake decreased when the initial concentration increased. The adsorption of Cr(VI) and Pb(II) ions on both adsorbents increased with temperature.

Corn stalk-based activated carbon synthesized by a novel activation method for high-performance adsorption of hexavalent chromium in aqueous solutions

A simple activation method involving treatment with KOH solution was used to synthesize activated carbon (ACs) with micro-meso pores from the agricultural waste of corn stalks. The activation reagent, KOH solution, was easily separated for recycling by centrifugation from the pre-treated corn stalks, and the pollution in the carbonization process was greatly reduced. The morphology and structure of the ACs were characterized by SEM, TEM, N₂ adsorption, XRD, FT-IR and Raman analysis. The prepared carbon was applied as an adsorbent for the removal of Cr(VI) in a batch adsorption process. The effect of the concentration of KOH solution on the structure, morphology and Cr(VI) adsorption performance of the synthesized ACs was investigated. The characterization results revealed that some functional groups in the corn stalks were removed by pretreatment with KOH solution and micro-meso porous structures were generated. The ACs showed high adsorption performance for Cr(VI), and the maximum adsorption ability of the ACs prepared by activation with 4% KOH solution reached 89.5 mg g^-1 at an adsorbent dosage of 2.5 g·L^-1 and pH value of 4.5.

Superior dye degradation and adsorption capability of polydopamine modified Fe3O4-pillared bentonite composite

Owing to the increasing demand of environmentally benign materials for the degradation of hazardous dyes, herein we are reporting two different synthesis approaches for the fabrication of iron loaded bentonite composites by modifying and activating bentonite surface with polydopamine (PDA) followed by pillaring with Fe³⁺ (Fe-PDA-bentonite) and Fe₃O₄ (Fe₃O₄-PDA-bentonite). Both the composites were assessed for their adsorption and degradation performance using crystal violet (CV), Rhodamine B and Brilliant blue dyes following adopting advanced oxidation process type Fenton reaction under variable energy sources (Sunlight, UV light and Ultrasonication), concentration of H₂O₂ and catalyst dosage. Under UV light irradiation, the composites achieved complete degradation of the dyes within 60 min and showed degradation rate constant of 30.5E-3-81.8E-3. Textural characterizations of the composites were achieved via XRD, FTIR, TGA, XPS, SEM-EDX, TEM, N₂ adsorption, VSM and UV/Vis spectrophotometry. The adsorption data of CV over the two composites fitted well with Langmuir adsorption isotherm, exhibiting the maximum adsorption capacity of 862 mg/g and 1235 mg/g for Fe-PDA-bentonite and Fe₃O₄-PDA-bentonite composites respectively. LCMS analysis of the post degradation products revealed that both the composites followed different degradation pathways and Fe₃O₄-PDA-bentonite showed superior photocatalytic performance by accomplishing complete dye degradation without leaving any degradation products. FTIR analysis of the post-degradation composites confirmed their structural stability with negligible iron leaching. This study, accredited to its cost-effectiveness, ease of operation and high efficiency, provides useful reference information for the degradation of dyes on industrial level.

Removal mechanisms of Cr(VI) and Cr(III) by biochar supported nanosized zero-valent iron: Synergy of adsorption, reduction and transformation

In this study, sludge-derived biochar was prepared and utilized to support nano-zero-valent iron (NZVI-SDBC) for removing Cr(VI) and Cr(III) from aqueous solution with the aim of investigating their removal and transformation. Under the conditions of initial pH of 4, dosage of 1 g/L, temperature of 25 °C, and rotational speed of 160 rpm, 64.13% Cr species could be removed by NZVI-SDBC from Cr(VI) solution and 28.89% from Cr(III) solution. Coexisting ions experiments showed that Cu(II) and humic acids dramatically affected the removal of Cr(VI) and Cr(III), while the effect of Na(I) and Ca(II) was almost negligible. Based on this, through the coexistence and pre-loaded Cr(III) experiments, the conversion from Cr(VI) to Cr(III) was demonstrated to enhance the further attraction on Cr(VI) and promote the subsequent removal of Cr(VI). The SDBC of NZVI-SDBC could serve as electron shuttle mediator to facilitate the electron transfer between adsorbed Cr(VI) and NZVI for ortho-reduction. The transformation and removal mechanisms were further discussed by various characterizations. The kinetics of Cr(VI) removal suggested that the removal process of Cr(VI) could be divided into three phases dominated by different mechanisms (adsorption, direct/ortho reduction, electrostatic attraction), in which Cr(VI) and Cr(III) showed different behaviors of interaction. The removal of Cr(III) mainly depended on sufficient adsorption sites and the direct complexation with Fe(II). Finally, the reusability of NZVI-SDBC was assessed by adsorption/desorption recycling test. These results provided new insights into the removal and transformation mechanisms of Cr(VI) and Cr(III) by biochar-based nanocomposites.

Synthesis of Fe-impregnated biochar from food waste for Selenium(Ⅵ) removal from aqueous solution through adsorption: Process optimization and assessment

Iron-impregnated food waste biochar (Fe-FWB) was synthesized for Se(Ⅵ) removal from aqueous solution. The effect and interactive effects of different parameters including pyrolysis time, temperature, and Fe concentration were explored using response surface methodology (RSM) to enhance conditions to achieve the highest Se(Ⅵ) removal using Fe-FWB. Pyrolysis time was not significant for Se(Ⅵ) adsorption capacity of Fe-FWB, but temperature and Fe concentration were found to be significant. The highest adsorption was achieved at 3.47 h and 495.0 °C with an Fe concentration of 0.44 M. Fe-FWB synthesized under optimum conditions were used to investigate the kinetic, equilibrium, and thermodynamic adsorption of Se(Ⅵ). Se(Ⅵ) adsorption reached equilibrium within 6 h, and both pseudo-second order and pseudo-first order models were suitable for describing kinetic Se(Ⅵ) adsorption. The Freundlich model was found to suitably fit the equilibrium adsorption data than the Langmuir model. The highest adsorption capacity of Fe-FWB for Se(Ⅵ) was 11.7 mg g^-1. Se(Ⅵ) adsorption on Fe-FWB was endothermic and spontaneous. The enthalpy change for Se(Ⅵ) adsorption was 54.4 kJ mol^-1, and the entropy change was negative at 15-35 °C. The increment of solution pH from 3 to 11 decreased the Se(Ⅵ) adsorption from 19.2 to 7.4 mg g^-1. The impact of interfering anions on Se(Ⅵ) adsorption followed the lineup: HCO₃^- > HPO₄^2- > SO₄^2- > NO₃^-. When compared to some adsorbents, the adsorption capacity of Se(Ⅵ) onto Fe-FWB was comparable even at neutral pH and the Fe-FWB was granular. These results indicate that Fe-FWB has prospective application in the removal of Se(Ⅵ) from aqueous solutions.

Efficient As(III) Removal by Novel MoS2-Impregnated Fe-Oxide-Biochar Composites: Characterization and Mechanisms

Sorbents that efficiently eliminate toxic metal(loid)s from industrial wastes are required for the protection of the environment and human health. Therefore, we demonstrated efficient As(III) removal by novel, eco-friendly, hydrothermally prepared MoS₂-impregnated FeO _x @BC800 (MSF@BC800). The properties and adsorption mechanism of the material were investigated by X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The synergistic effects of FeO _x and MoS₂ on MSF@BC800 considerably enhanced As(III)-removal efficiency to ≥99.73% and facilitated superior As(III) affinity in aqueous solutions (K _d ≥ 10⁵ mL g^-1) compared to those of FeO _x @BC800 and MS@BC800, which showed 37.07 and 17.86% As(III)-removal efficiencies and K _d = 589 and 217 mL g^-1, respectively, for an initial As(III) concentration of ∼10 mg L^-1. The maximum Langmuir As(III) sorption capacity of MSF@BC800 was 28.4 mg g^-1. Oxidation of As(III) to As(V) occurred on the MSF@BC800 composite surfaces. Adsorption results agreed with those obtained from the Freundlich and pseudo-second-order models, suggesting multilayer coverage and chemisorption, respectively. Additionally, MSF@BC800 characteristics were examined under different reaction conditions, with temperature, pH, ionic strength, and humic acid concentration being varied. The results indicated that MSF@BC800 has considerable potential as an eco-friendly environmental remediation and As(III)-decontamination material.

Preparation, environmental application and prospect of biochar-supported metal nanoparticles: A review

Biochar is a low-cost, porous, and carbon-rich material and it exhibits a great potential as an adsorbent and a supporting matrix due to its high surface activity, high specific surface area, and high ion exchange capacity. Metal nanomaterials are nanometer-sized solid particles which have high reactivity, high surface area, and high surface energy. Owing to their aggregation and passivation, metal nanomaterials will lose excellent physiochemical properties. Carbon-enriched biochar can be applied to overcome these drawbacks of metal nanomaterials. Combining the advantages of biochar and metal nanomaterials, supporting metal nanomaterials on porous and stable biochar creates a new biochar-supported metal nanoparticles (MNPs@BC). Therefore, MNPs@BC can be used to design the properties of metal nanoparticles, stabilize the anchored metal nanoparticles, and facilitate the catalytic/redox reactions at the biochar-metal interfaces, which maximizes the efficiency of biochar and metal nanoparticles in environmental application. This work detailedly reviews the synthesis methods of MNPs@BC and the effects of preparation conditions on the properties of MNPs@BC during the preparation processes. The characterization methods of MNPs@BC, the removal/remediation performance of MNPs@BC for organic contaminants, heavy metals and other inorganic contaminants in water and soil, and the effect of MNPs@BC properties on the remediation efficiency were discussed. In addition, this paper summarizes the effect of various parameters on the removal of contaminants from water, the effect of MNPs@BC remediation on soil properties, and the removal/remediation mechanisms of the contaminants by MNPs@BC in water and soil. Moreover, the potential directions for future research and development of MNPs@BC have also been discussed.

Simultaneous reduction of nitrate and Cr(VI) by Pseudomonas aeruginosa strain G12 in wastewater

The interference of toxic heavy metals in the process of microbial aerobic denitrification is a hot issue in industry wastewater treatment in recent years. In this study, a multifunctional aerobic denitrifying bacterium - Pseudomonas aeruginosa G12 isolated from sewage sludge was used to explore the simultaneous removal ability to NO₃^--N and Cr(VI) in wastewater by a series of batch experiments. The results showed that G12 could effectively remove NO₃^--N (500 mg L^-1) and Cr(VI) (10 mg L^-1) by 98% and 93%, respectively. Meanwhile, the study found that the strain G12 had the potential to adapt to the complex external environment, including different carbon resources, nitrogen sources, and the coexisting heavy metals (Mn²⁺ and Cu²⁺). The strain G12 also had the considerable tolerance to initial NO₃^--N (100-700 mg L^-1) and Cr(VI) (1-20 mg L^-1) concentrations. The instrument analysis methods-Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), from the molecular level, further confirmed that the strain G12 could remove NO₃^--N by aerobic denitrification, and the reduced functional groups (amino group, amide group, hydroxyl group and carboxyl group) on the surface of bacteria could transform Cr(VI) to Cr(III) (mainly CrCl₃). This study will offer a promising new microbial resource for nitrogen and Cr(VI) removal in industry wastewater treatment.