Removal of arsenate from contaminated waters by novel zirconium and zirconium-iron modified biochar

Confinement-induced Ni-based MOF formed on Ti3C2Tx MXene support for enhanced capacitive deionization of chromium(VI)

MXenes, as a novel two-dimensional lamellar material, has attracted much attention. However, MXenes lamellar are prone to collapse and stacking under hydrogen bonding and interlayer van der Waals forces, which affects their electrochemical and capacitive deionization performance. A three-dimensional Ni-1,3,5-benzenetricarboxylate/Ti3C2Tx (Ni-BTC/Ti3C2Tx) composite electrode material was developed to enhance the electrochemical and capacitive deionization performance. The uniformly decorated Ni-BTC can prevent MXenes from aggregation and provide a large specific surface area and rich pore structure. As a substrate supporting Ni-BTC, MXenes can effectively disperse the growth of Ni-BTC and enhance the ion transport rate. In addition, the unique three-dimensional structure of Ni-BTC/Ti3C2Tx provides horizontal charge transfer paths like two-dimensional nanosheets and has unique vertical charge transfer paths between nanosheets. Therefore, the Ni-BTC/Ti3C2Tx exhibits an exceptional chromium(VI) removal rate of 94.1%. The electrosorption capacity of the Ni-BTC/Ti3C2Tx for chromium(VI) is 124.5 mg g-1, much higher than that of the pure Ti3C2Tx (55.5 mg g-1). The superior CDI efficiency accomplished through the Ni-BTC/Ti3C2Tx electrode is due to the unique three-dimensional network structure and synergistic effect of the pseudocapacitance generated by the unique assembly of Ni-BTC and Ti3C2Tx. Ni-BTC/Ti3C2Tx is a promising CDI electrode material that can be used for capacitive deionization.

Eco-Friendly Carbon Nanotubes Reinforced with Sodium Alginate/Polyacrylic Acid for Enhanced Adsorption of Copper Ions: Kinetics, Isotherm, and Mechanism Adsorption Studies

This study investigates the removal efficiency of Cu2+ from wastewater using a composite hydrogel made of carbon nanotubes (CNTs), sodium alginate (SA), and polyacrylic acid (PAA) prepared by free radical polymerization. The CNTs@SA/PAA hydrogel's structure and properties were characterized using SEM, TEM, FTIR, XRD, rheology, DSC, EDS, elemental mapping analysis, and swelling. The adsorption performance for Cu2+ was tested in batch adsorption experiments, considering the pH, dosage, initial concentration, and contact time. The optimal conditions for Cu2+ removal were pH 5.0, an adsorbent dosage of 500 mg/L, and a contact time of 360 min. The adsorption followed pseudo-second order kinetics. Isotherm analyses (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Sips, Toth, and Khan) revealed that the Freundlich isotherm best described the adsorption, with a maximum capacity of 358.52 mg/g. A thermodynamic analysis indicated that physical adsorption was the main interaction, with the spontaneity of the process also demonstrated. This study highlights the high efficiency and environmental friendliness of CNT@SA/PAA composites for Cu2+ removal from wastewater, offering a promising approach for water treatment.

Saline-alkali soil amended with biochar derived from maricultural-solid-waste: Ameliorative effect and mechanism

At present, it is estimated that approximately 800 million hectares of arable land worldwide is saline-alkali soil, which has become one of the major limiting factors restricting global agricultural productivity. Meanwhile, the residual food and excreta of mariculture animals, accompanied by potential eutrophication pollution, remain an unresolved issue due to salinity. In this study, the ameliorative effects of biochar (BC700) prepared from maricultural-solid-waste on the biological properties and physicochemical of saline-alkali soil and Salicornia europaea L growth were investigated. Supplements of 1, 3 and 5% BC700 significantly increased the total nitrogen, available phosphorus, available potassium and organic carbon in soil by 2.00-68.30%, 26.74-64.96%, 7.74-52.53% and 3.43-64.96%, respectively. And BC700 significantly reduced soil pH. This occurred with enhanced soil urease, sucrase and alkaline phosphatase activities and alterations to the bacterial community structure, thus improving P and N cycling and the soil physicochemical properties. In addition, BC700 has weakened the competition between saline soil microorganisms and also changed the key species of microbial networks. Co-utilization of BC700 and S. europaea cultivation could increase the stability of the soil microbial community while the growth of the plant was significantly promoted by 19.8-25.4%. Supplements of 3% BC700 are recommended as an eco-friendly and effective treatment for the recycling of mariculture wastes for the improvement of saline-alkali soils.

A mechanistic approach to arsenic adsorption and immobilization in aqueous solution, groundwater, and contaminated paddy soil using pine-cone magnetic biochar

Arsenic (As) poisoning in groundwater and rice paddy soil has increased globally, impacting human health and food security. There is an urgent need to deal with As-contaminated groundwater and soil. Biochar can be a useful remedy for toxic contaminants. This study explains the synthesis of pinecone-magnetic biochar (PC-MBC) by engineering the pinecone-pristine biochar with iron salts (FeCl3.6H2O and FeSO4.7H2O) to investigate its effects on As(V) adsorption and immobilization in water and soil, respectively. The results indicated that PC-MBC can remediate As(V)-contaminated water, with an adsorption capacity of 12.14 mg g-1 in water. Isotherm and kinetic modeling showed that the adsorption mechanism involved multilayer, monolayer, and diffusional processes, with chemisorption operating as the primary interface between As(V) and biochar. Post-adsorption analysis of PC-MBC, using FTIR and XRD, further revealed chemical fixing and outer-sphere complexation between As(V) and Fe, O, NH, and OH as the main reasons for As(V) adsorption onto PC-MBC. Recycling of PC-MBC also had excellent adsorption even after several regeneration cycles. Similarly, PC-MBC successfully immobilized As in paddy soil. Single and sequential extraction results showed the transformation of mobile forms of As to a more stable form, confirmed by non-destructive analysis using SEM, EDX, and elemental dot mapping. Thus, Fe-modified pine-cone biochar could be a suitable and cheap adsorbent for As-contaminated water and soil.

Novel heterogeneous Fenton catalysts for promoting carbon iron electron transfer by one-step hydrothermal synthesization

Carbon materials play a crucial role in promoting the Fe(III)/Fe(II) redox cycle in heterogeneous Fenton reactions. However, the electron transfer efficiency between carbon and iron is typically low. In this study, we prepared a novel heterogeneous Fenton catalyst, humboldtine/hydrothermal carbon (Hum/HTC), using a one-step hydrothermal method and achieved about 100 % reduction in Fe(III) during synthesis. Moreover, the HTC continuously provided electrons to promote Fe(II) regeneration during the Fenton reaction. Electron paramagnetic resonance (EPR) and quenching experiments showed that Hum/HTC completely oxidized As(III) to As(V) via free radical and non-free radical pathways. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and two-dimensional correlation spectroscopy (2D-COS) analyses revealed that monodentate mononuclear (MM) and bidentate binuclear (BB) structures were the dominant bonding methods for As(V) immobilization. 40 %Hum/HTC exhibited a maximum As(III) adsorption capacity of 167 mg/g, which was higher than that of most reported adsorbents. This study provides a novel strategy for the efficient reduction of Fe(III) during catalyst synthesis and demonstrates that HTC can continuously accelerate Fe(II) regeneration in heterogeneous Fenton reactions.

Biochar performance for preventing cadmium and arsenic accumulation, and the health risks associated with mustard (Brassica juncea) grown in co-contaminated soils

Cadmium (Cd) and arsenic (As) in co-contaminated soil can enter the human body harming health via the food chain, such as vegetables. Biochar derived from waste has been used to reduce heavy metal uptake by plant, but long-term effects of biochar under Cd and As co-contaminated soil needs to be investigated. A following mustard (Brassica juncea) was grown on co-contaminated soil amended with different raw materials of biochar including biochars pyrolyzed by lignite coal (LCB), rice straw (RSB), silkworm excrement (SEB), and sugar refinery sludge (SSB). The results showed that compared to the control, Cd and As contents of mustard shoot in SSB treatment decreased by 45-49% and 19-37% in two growing seasons, respectively, which was the most effective among 4 biochars. This probably due to SSB owns more abundant Fe-O functional groups. Biochar also altered the microbial community composition, specifically SSB increased proteobacteria abundance by 50% and 80% in the first and second growing seasons, thereby promoted the simultaneous immobilization of Cd and As in soils which may reduce the potential risks to humans. In summary, considering the long-term effects and security of SSB application on mustard, not only is it an effective waste recycle option, but it should also be promoted as a promising approach for safe vegetable production in Cd and As co-contaminated soils.

Enhancing arsenic adsorptions by optimizing Fe-loaded biochar and preliminary application in paddy soil under different water management strategies

Arsenic (As) is widely distributed in nature and is a highly toxic element impacting human health through drinking water and rice. In this study, an optimized approach was attempted to improve As adsorption capabilities by combining pre- and post-pyrolysis modification of Fe(oxy)hydroxides to rice husk biochar (FRB), of which the method is rarely addressed in previous studies. Maghemite and goethite were successfully loaded onto biochar, characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoemission spectroscopy (XPS) analyzer. The FRB had maximum As(III) and As(V) adsorption capabilities of 7908 and 11,268 mg/kg, respectively, which was significantly higher than that of Fe-modified biochar in the pre-pyrolysis and/or post-pyrolysis process. Adsorption mechanisms for As explored by Fourier-transform infrared spectroscopy (FTIR), XPS analysis mainly included electronic attraction and ligand exchange with hydroxyl groups on the FRB. It was noteworthy that more than half of the As(II) species loaded on FRB were converted into less toxic As(V) species, which could be mediated by the redox-active groups on the biochar. The preliminary application of FRB in soil indicated that it has an effective remediation potential for As-contaminated soil under flooded conditions, while promoted As release under dry conditions. Finding of this study highlighted that the loading of metal oxides onto biochar by combining pre- and post-pyrolysis modification could potentially increase As adsorption capabilities and further help in strategic water management.

Remediation of cadmium contaminated soil using K2FeO4 modified vinasse biochar

The remediation of cadmium (Cd) contaminated soil is challenging for agricultural practices. In this study, a novel vinasse biochar modified by potassium ferrate (K₂FeO₄) was synthesized to immobilize Cd in agricultural soil. Three biochars [i.e., vinasse biochar (BC), KMnO₄ modified vinasse biochar (MnBC), and K₂FeO₄ modified vinasse biochar (FeBC)] were applied to compare their efficiencies of Cd immobilization. The results showed that the orders of pH, ash content, and functional groups in different biochar were the same following BC < MnBC < FeBC. Scanning electron microscope images showed that the FeBC has more micropores than MnBC and BC. X-ray diffraction identified manganese oxides and iron oxides within MnBC and FeBC, indicating that Mn and Fe were well loaded on the biochar. In the soil-based pot experiment, both MnBC and FeBC significantly reduced soil available Cd by 23-38% and 36-45% compared with the control, respectively (p < 0.05). In addition, the application of BC, MnBC, and FeBC significantly increased the yield, chlorophyll, and vitamin C of Chinese cabbage (p < 0.05), and decreased its Cd uptake compared with the control. Notably, shoot Cd significantly reduced when 2% FeBC was applied (p < 0.05). Overall, using K₂FeO₄ to modify vinasse biochar enriched the surface functional groups and minerals as well as reduced Cd availability in soil and its uptake by the plant. Our study showed that K₂FeO₄ modified vinasse biochar could be used as an ideal amendment for the remediation of Cd-contaminated soil.

Biochar modification to enhance arsenic removal from water: a review

Arsenic (As) contamination is a major threat to drinking water quality throughout the world, and the development of appropriate remediation methods is critical. Adsorption is considered the most effective method for remediation of As-contaminated water. Biochar is a promising adsorbent and widely discussed for As removal due to its potential low cost and environmental friendliness. However, pristine biochar generally exhibited relatively low adsorption capacity for As mainly due to the electrostatic repulsion between the negatively charged biochar and As. Biochar modification, especially metal modification, was developed to boost the adsorption capacity for As. A systematic analysis of As removal as affected by biochar properties and modification will be of great help for As removal. This paper presents a comprehensive review on As removal by biochars from different feedstock, preparation procedures, and modification methods, with a major focus on the possible mechanisms of interaction between As and biochar. Biochar derived from sewage sludge exhibited relatively high adsorption capacity for As. Considering energy conservation, biochars prepared at 401-500 °C were more favorable in adsorbing As. Fe-modified biochar was the most popular modified biochar for As remediation due to its low cost and high efficiency. In addition, the limitations of the current studies and future perspectives are presented. The aim of this review is to provide guidance for the preparation of low-cost, environmentally friendly, and high efficiency biochar for the remediation of As-contaminated water.

Fe-Ni/MWCNTs Nano-Composites for Hexavalent Chromium Reduction in Aqueous Environment

A novel Cr (VI) removal material was designed and produced comprising multi-walled carbon nanotubes (MWCNTs) as a support with a high specific surface area and the loaded Fe-Ni bimetallic particles as catalytic reducing agents. Such a design permits the composite particle to perform the adsorption, reduction, and immobilisation of Cr (VI) quickly and efficiently. Due to MWCNTs' physical adsorption, Cr (VI) in solution aggregates in the vicinity of the composite, and Fe rapidly reduces Cr (VI) to Cr (III) catalysed by Ni. The results demonstrated that the Fe-Ni/MWCNTs exhibits an adsorption capacity of 207 mg/g at pH = 6.4 for Cr (VI) and 256 mg/g at pH 4.8, which is about twice those reported for other materials under similar conditions. The formed Cr (III) is solidified to the surface by MWCNTs and remains stable for several months without secondary contamination. The reusability of the composites was proven by retaining at least 90% of the adsorption capacity for five instances of reutilization. Considering the facile synthesis process, low cost of raw material, and reusability of the formed Fe-Ni/MWCNTs, this work shows great potential for industrialisation.

High-efficient and rapid removal of anionic and cationic dyes using a facile synthesized sole adsorbent NiAlFe-layered triple hydroxide (LTH)

It would be extremely momentous to familiarize a low-cost sole adsorbent NiAlFe-layered triple hydroxides (LTHs) having a strong sorption affinity towards both anionic and cationic dyes. Using the urea hydrolysis hydrothermal method LTHs were fabricated and by altering the ratio of participant metal cations the adsorbent was optimized. BET analysis revealed that the optimized LTHs possess an elevated surface area (160.04 m²/g) while TEM and FESEM analysis portrayed the stacked sheets-like 2D morphology. LTHs were employed for the amputation of anionic congo red (CR) and cationic brilliant green (BG) dye. The adsorption study showed that within 20 and 60 min, respectively, maximum adsorption capacities were achieved at 57.47 mg/g and 192.30 mg/g for CR and BG dye. Adsorption isotherm, kinetics, and thermodynamics study revealed that both chemisorptions with physisorptions were the assertive factor for the dye encapsulation. This enhanced adsorption performance of the optimized LTH for the anionic dye is attributed to its inherent anions exchange properties and new bond formation with the adsorbent skeleton. Whereas for the cationic dye, it was because of the formation of strong hydrogen bonds, and electrostatic interaction. Morphological manipulation of LTHs, formulates the optimized adsorbent LTH111, provokes the adsorbent for this elevated adsorption performance. Overall, this study revealed that LTHs have a high potential for the effectual remediation of dyes from wastewater as a sole adsorbent at a low cost.

Directional regulation and mechanism analysis of the surface properties of hydrothermal carbon by circulating liquid in the hydrothermal carbonization procedure

The complexity of the chemistry behind the hydrothermal conversion is enormous. Components interact with their own physical and chemical structure, making it harsh to understand the conversion as a whole. Herein, the six-water recirculation and loading nano SiO₂ experiment in a one-pot hydrothermal carbonization procedure was designed to elucidate the mechanism of regulating the functional groups and microporous structure of the hydrochar surface. The hydrochar prepared by the second circulating liquid and loading nano-SiO₂ (HBC-R2/Si) was equipped most enriched functional groups (carboxyl = 11.48 μmol/g, phenolic hydroxyl = 52.98 μmol/g, lactone groups = 46.52 μmol/g) and suitable pore size (1.90 nm-1.93 nm) as a sorbent riched in hemicellulose. The sorption kinetics (equilibrium reached ≈ 480 min) are approximately evenly fitted by the pseudo-second-order, Weber and Morris, and Elovich models, indicating that membranes and particles diffusion, pore diffusion, and surface sorption coexisted in the sorption of methylene blue (MB) on the hydrochar materials. Simultaneously, all hydrochar materials achieved over 25% MB removal within 90 min (liquid membrane diffusion) and over 40% for HBC-R2 and HBC-R2/Si, suggesting that liquid membrane diffusion is the predominant rate-limiting step. Pearson's correlation analysis and Mantel's analysis announced that the cation exchange capacity (CEC), pore size, and carboxyl groups on the hemicellulose affect the sorption capacity by limiting the pore diffusion procedure. However, the CEC and the phenolic hydroxyl groups on the cellulose and hemicellulose affect the sorption rate by limiting membrane diffusion. Three consecutive sorption/desorption cycles confirmed the high stability and reusability of HBC-R2/Si composites.

Adsorption of chitosan combined with nicotinamide-modified eupatorium adenophorum biochar to Sb3+: Application of DFT calculation

The pollution and harm of Sb³⁺ to aquatic systems is a global problem, so Sb³⁺ removal from the water environment to make sure environment safety and human beings wellbeing is of urgency. This study explored the effect of chitosan combined with nicotinamide-modified eupatorium adenophorum biochar (CEBC) on adsorbing Sb³⁺ through batch adsorption experiments. The experiments indicated CEBC's maximum adsorption capacity to Sb³⁺ is 170.15 mg·g^-1. Meanwhile, the capacity of the original biochar (EBC) is only 9.97 mg·g^-1. Compared with EBC, CEBC contains more functional groups, such as CO, -OH and -NH₂. In addition, the pseudo-second-order kinetic model and the Langmuir model are fit to describe the kinetics and isotherms of adsorption of CEBC to Sb³⁺, which suggests that the adsorption of CEBC to Sb³⁺ is dominated by monolayer chemisorption. Density functional theory (DFT) calculations confirmed that the chelation between -NH₂ and Sb³⁺ is of significance in the adsorption process of CEBC. DFT calculations also found that the newly added -OH and CO in EBC have a synergistic enhancement effect on the absorption of Sb³⁺. The mechanism of CEBC absorbing Sb³⁺ includes electrostatic interactions, pore filling, Л-Л interactions, hydrogen bonding, functional group complexation, chelation, and oxidation. CEBC has an excellent anti-interference ability for inorganic anions (NO₃^-, SO₄^2- and Cl^-) and can also use the coexisting HA to improve its adsorption performance. In addition, CEBC has better mitigation of Sb³⁺ on the performance of Sb³⁺ about its secondary release and good reproducibility, which indicates that CEBC is a viable Sb³⁺ adsorbent.

A Comprehensive Review of the Current Progress of Chromium Removal Methods from Aqueous Solution

Chromium (Cr) exists in aqueous solution as trivalent (Cr³⁺) and hexavalent (Cr⁶⁺) forms. Cr³⁺ is an essential trace element while Cr⁶⁺ is a dangerous and carcinogenic element, which is of great concern globally due to its extensive applications in various industrial processes such as textiles, manufacturing of inks, dyes, paints, and pigments, electroplating, stainless steel, leather, tanning, and wood preservation, among others. Cr³⁺ in wastewater can be transformed into Cr⁶⁺ when it enters the environment. Therefore, research on Cr remediation from water has attracted much attention recently. A number of methods such as adsorption, electrochemical treatment, physico-chemical methods, biological removal, and membrane filtration have been devised for efficient Cr removal from water. This review comprehensively demonstrated the Cr removal technologies in the literature to date. The advantages and disadvantages of Cr removal methods were also described. Future research directions are suggested and provide the application of adsorbents for Cr removal from waters.

Effective biosorption of As(V) from polluted water using Fe(III)-modified Pomelo (Citrus maxima) peel: A batch, column, and thermodynamic study

Pomelo, Citrus maxima, peel was chemically modified with lime water and then loaded with Fe(III) to develop anion exchange sites for effective sequestration of As(V) from water. Biosorbent characterizations were done by using FTIR, SEM, XRD, EDX, and Boehm's titration. The batch biosorption studies were carried out at various pHs using modified and non-modified biosorbents and optimum biosorption of As(V) occurred at acidic pH (3.0-5.0) for both the biosorbents. A kinetic study showed a fast biosorption rate and obtained results fitted well with the pseudo-second-order (PSO) model. When isotherm data were modeled using the Langmuir and Freundlich isotherm models, the Langmuir isotherm model fit the data better and produced maximal As(V) biosorption capacities of 0.72 ± 03, 0.86 ± 06, and 0.95 ± 05 mmol/g at temperatures 293± 1K, 298± 1K and 303± 1K, respectively. Desorptionof As(V) was effective using 0.1 M NaOH in batch mode. Negative values of ΔG° for all temperatures with positive ΔH° confirmed the spontaneous and endothermic nature of As(V) biosorption. The existence of co-existing chloride (Cl^-), nitrate (NO₃ ^-), sodium (Na⁺), and calcium (Ca²⁺) showed insignificant interference whereas a high concentration of sulphate (SO₄ ^2-) and phosphate (PO₄ ^3-) significantly lowered As(V) biosorption percentage. Arsenic concentrations in actual arsenic polluted groundwater could be reduced to the WHO drinking water standard (10 μg/L) by using only 1 g/L of investigated Fe(III)-SPP. The dynamic biosorption of As(V) in a fixed bed system showed that Fe(III)-SPP was effective also in continuous mode and different design parameters for fixed bed system were determined using Thomas, Adams-Bohart, BDST, and Yoon-Nelson models. Therefore, from all of these results it is suggested that Fe(III)-SPP investigated in this study can be a potential, low cost and environmentally benign biosorbent material for an effective removal of trace amounts of arsenic from polluted water.

Effective Usage of Biochar and Microorganisms for the Removal of Heavy Metal Ions and Pesticides

The bioremediation of heavy metal ions and pesticides is both cost-effective and environmentally friendly. Microbial remediation is considered superior to conventional abiotic remediation processes, due to its cost-effectiveness, decrement of biological and chemical sludge, selectivity toward specific metal ions, and high removal efficiency in dilute effluents. Immobilization technology using biochar as a carrier is one important approach for advancing microbial remediation. This article provides an overview of biochar-based materials, including their design and production strategies, physicochemical properties, and applications as adsorbents and support for microorganisms. Microorganisms that can cope with the various heavy metal ions and/or pesticides that enter the environment are also outlined in this review. Pesticide and heavy metal bioremediation can be influenced by microbial activity, pollutant bioavailability, and environmental factors, such as pH and temperature. Furthermore, by elucidating the interaction mechanisms, this paper summarizes the microbe-mediated remediation of heavy metals and pesticides. In this review, we also compile and discuss those works focusing on the study of various bioremediation strategies utilizing biochar and microorganisms and how the immobilized bacteria on biochar contribute to the improvement of bioremediation strategies. There is also a summary of the sources and harmful effects of pesticides and heavy metals. Finally, based on the research described above, this study outlines the future scope of this field.

Remediation of cadmium or arsenic contaminated water and soil by modified biochar: A review

Biochar has a high specific surface area with abundant pore structure and functional groups, which has been widely used in remediation of cadmium or arsenic contaminated water and soil. However, the bottleneck problem of low-efficiency of pristine biochar in remediation of contaminated environments always occurs. Nowadays, the modification of biochar is a feasible way to enhance the performance of biochar. Based on the Web of science™, the research progress of modified biochar and its application in remediation of cadmium or arsenic contaminated water and soil have been systematically summarized in this paper. The main modification strategies of biochar were summarized, and the variation of physicochemical properties of biochar before and after modification were illustrated. The efficiency and key mechanisms of modified biochar for remediation of cadmium or arsenic contaminated water and soil were expounded in detail. Finally, some constructive suggestions were given for the future direction and challenges of modified biochar research.

Biochar for the removal of contaminants from soil and water: a review

Biochar shows significant potential to serve as a globally applicable material to remediate water and soil owing to the extensive availability of feedstocks and conducive physio-chemical surface characteristics. This review aims to highlight biochar production technologies, characteristics of biochar, and the latest advancements in immobilizing and eliminating heavy metal ions and organic pollutants in soil and water. Pyrolysis temperature, heat transfer rate, residence time, and type of feedstock are critical influential parameters. Biochar’s efficacy in managing contaminants relies on the pore size distribution, surface groups, and ion-exchange capacity. The molecular composition and physical architecture of biochar may be crucial when practically applied to water and soil. In general, biochar produced at relatively high pyrolysis temperatures can effectively manage organic pollutants via increasing surface area, hydrophobicity and microporosity. Biochar generated at lower temperatures is deemed to be more suitable for removing polar organic and inorganic pollutants through oxygen-containing functional groups, precipitation and electrostatic attraction. This review also presents the existing obstacles and future research direction related to biochar-based materials in immobilizing organic contaminants and heavy metal ions in effluents and soil.

Graphical Abstract

Novel magnetic Fe@NSC nanohybrid material for arsenic removal from aqueous media

Polymer-derived carbon nanohybrids present a remarkable potential for the elimination of water pollutants. Herein, an Fe-modified C, N, and S (Fe@NSC) nanohybrid network, synthesized via polymerization of aniline followed by calcination, is used for As removal from aquatic media. The Langmuir isotherm and pseudo-second-order kinetic models fit well the experimental data for the adsorptive removal of As(III) and As(V) by the as-synthesized Fe@NSC nanohybrid, indicating that adsorption is a monolayer chemisorption process. The maximum adsorption capacities of the fabricated Fe@NSC nanohybrid for As(III) and As(V) were 129.54 and 178.65 mg/g, respectively, which are considerably higher than those reported previously for other adsorbents. In particular, the Fe₃O₄/FeS nanoparticles (18.4-38.7 nm) of the prepared Fe@NSC nanohybrid play a critical role in As adsorption and oxidation. Spectroscopy data indicate that the adsorption of As on Fe@NSC nanohybrid involved oxidation, ligand exchange, surface complexation, and electrostatic attraction. Furthermore, the magnetic Fe@NSC nanohybrid was easily separated after As adsorption using an external magnet and did not induce acute toxicity (48 h) in Daphnia magna. Moreover, the Fe@NSC nanohybrid selectively removed As species in the presence of competing anions and was effectively regenerated for up to three cycles using a 0.1 M HNO₃ solution. These findings suggest that Fe@NSC nanohybrid is a promising adsorbent for As remediation in aquatic media.

Adsorptive removal of Ag/Au quantum dots onto covalent organic frameworks@magnetic zeolite@arabic gum hydrogel and their catalytic microwave-Fenton oxidative degradation of Rifampicin antibiotic

Recent progress in nanotechnology via incorporation of small particle size as quantum dots (QDs) (1-10 nm) in many industrial activities and commercial products has led to significant undesired environmental impacts. Therefore, QDs removal from wastewater represents an interesting research topic with a lot of challenges for scientists and engineers nowadays. In this work, the coagulative removal of metal quantum dots as silver and gold from industrial water samples is explored. A novel biosorbent was assembled via binding of covalent organic frameworks (COFs) with magnetic zeolite and Arabic gum hydrogel (COFs@MagZ@AGH) as a promising removal material for Ag-QDs and Au-QDs. This was fully characterized by EDX, SEM, TEM, FT-IR, XPS, XRD and surface area and applied in coagulative removal of Au-QDs and Ag-QDs in presence of several experimental factors as pH, presence of other electrolytes, stirring time, initial QDs concentration, coagulant dosage, and temperature in order to optimize the removal processes. At optimum conditions, COFs@MagZ@AGH was able to recover 99.19% and 87.57% of Ag-QDs and Au-QDs QDs, respectively via chemical adsorption mechanism with perfect fitting to pseudo-second order model. Reuse of the recovered Ag/Au-QDs@COFs@MagZ@AGH as efficient catalysts in catalytic degradation of Rifampicin antibiotic (Rf) from water was additionally investigated and optimized via microwave-Fenton catalysts with excellent oxidative degradation efficiency (100%). Reusability and applicability of the biosorbent (COFs@MagZ@AGH) and catalysts (Ag/Au-QDs@COFs@MagZ@AGH) in real industrial water samples were also explored and successfully accomplished.

Zirconium-modified biochar as the efficient adsorbent for low-concentration phosphate: performance and mechanism

Achieving advanced treatment of phosphorus (P) to prevent water eutrophication and meet increasingly stringent wastewater discharge standard is an important goal of water management. In this study, a low-cost, high-efficiency phosphate adsorbent zirconium-modified biochar (ZrBC) was successfully synthesized through co-precipitation method, in which the biochar was prepared from the pyrolysis of peanut shell powder. ZrBC exhibited strong adsorption ability to low-concentration phosphate (< 1 mg·L^-1) in water, and the phosphate removal reached 100% at the investigated dosage range (0.1-1.0 mg·L^-1). The adsorption process could be described well by pseudo-second-order model and Langmuir isotherm model, indicating that the phosphate adsorption by ZrBC was mainly a chemical adsorption and single-layer adsorption process. The calculated static maximum phosphate adsorption capacity was 58.93 mg·g^-1 at 25 °C. The ligand exchange between surface hydroxyl groups and phosphate was the main mechanism for the phosphate adsorption on ZrBC. The presence of coexisting anions except for SO₄^2- had little effect on the phosphate removal. At the column experiment, ZrBC showed superior treatment capacities for simulated secondary effluents and the breakthrough time for 0.5 mg·L^-1 effluent phosphate concentration reached 190 h. ZrBC highlights the potential as an effective and environment-friendly adsorbent for the removal of low-concentration phosphate from secondary effluents of municipal wastewater treatment plants (WWTPs).

An insight into the act of iron to impede arsenic toxicity in paddy agro-system

Surplus research on the widespread arsenic (As) revealed its disturbing role in obstructing the metabolic function of plants. Also, the predilection of As towards rice has been an interesting topic. Contrary to As, iron (Fe) is an essential micronutrient for all life forms. Past findings propound about the enhanced As-resistance in rice plants during Fe supplementation. Thus, considering the severity of As contamination and resulting exposure through rice crops, as well as the studied cross-talks between As and Fe, we found this topic of relevance. Keeping these in view, we bring this review discussing the presence of As-Fe in the paddy environment, the criticality of Fe plaque in As sequestration, and the effectiveness of various Fe forms to overcome As toxicity in rice. This type of interactive analysis for As and Fe is also crucial in the context of the involvement of Fe in cellular redox activities such as oxidative stress. Also, this piece of work highlights Fe biofortification approaches for better rice varieties with optimum intrinsic Fe and limited As. Though elaborated by others, we lastly present the acquisition and transport mechanisms of both As and Fe in rice tissues. Altogether we suggest that Fe supply and Fe plaque might be a prospective agronomical tool against As poisoning and for phytostabilization, respectively.

Novel iron-supported ZSM-5 molecular sieve remove arsenic from wastewater by heterogeneous nucleation with pH limit breaking

Molecular sieves have also been used for arsenic adsorption in recent years because of their special structure. In order to solve the problem of arsenic pollution in drinking water and/or industrial wastewater, ZSM-5/Fe adsorbent was prepared by loading iron on ZSM-5 molecular sieve. It is also used as an excellent adsorbent for removing arsenic and other heavy metal ions from industrial wastewater. At room temperature, the concentration of arsenic was reduced from 100 mg/L to 0.006 mg/L after the solution pH was adjusted to the range of weak acid to weak base (4-10) and 0.5 g of ZSM-5/Fe adsorbent was added for reacting 2 h. The adsorption capacity reached 40.00 mg/g, the adsorption efficiency reached 99.99%, reaching the national standard of drinking water. Adsorption thermodynamics, kinetics and isotherms showed that the adsorption mechanism of arsenic is heterogeneous nucleation adsorption (including electrostatic attraction and chemical precipitation). Moreover, ZSM-5/Fe adsorbent can adjust pH spontaneously by using non-skeleton Si-Al phase to achieve effective adsorption from weak acid to weak base. At the same time, ZSM-5/Fe adsorbent showed good reusability and stability in five cycles. This study provides an important idea for the application of ZSM-5 molecular sieve in many fields and the efficient removal of arsenic from drinking water and industrial wastewater.

Efficient removal of arsenic from aqueous solution by continuous adsorption onto iron-coated cork granulates

The search for low-cost technologies for arsenic removal from water is in high demand due to its human toxicity, even at low concentrations. Adsorption can be a cost-effective water treatment technique if applied with inexpensive materials. Arsenic continuous removal by adsorption onto an alternative modified biosorbent, iron-coated cork granulates (ICG), was investigated in this work. Results showed that most experimental parameters of breakthrough curves (BTC) depend on flow rate, bed height, pH, and initial arsenic concentration. The temperature did not significantly affect arsenate removal in continuous mode; however, the adsorption capacity was affected in batch mode. The thermodynamic parameters suggest that the adsorption process is spontaneous and endothermic. The maximum adsorption capacity of ICG for As(V) removal at pH 3 was 4.2 ± 0.3 mg g^-1, calculated by Yan model fit (R² = 0.981), and for As(III) at pH 9 was 1.6 ± 0.2 mg g^-1 (R² = 0.994). ICG were able to treat As(V) from 100 µg L^-1 to under 10 µg L^-1 and 50 µg L^-1 for 895 and 1633 bed volumes, and As(III) for 569 and 861 bed volumes, respectively, both at pH 7. The application of ICG in arsenic oxyanions remediation was found to be effective under various conditions.

Synthesis and characterization of lanthanum-based metal organic framework decorated polyaniline for effective adsorption of lead ions from aqueous solutions

The novel La-MOF@x%PANI composite was synthesized via a two-step procedure with ultra-sonication, and the adsorption mechanism of Pb²⁺ ions from synthetic aqueous solutions was systematically studied. The Pb²⁺ adsorption on the La-MOF@x%PANI was evaluated by the Fourier transform infrared spectroscopy, powder X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray analysis, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy, and elemental mapping analyses. The effects of the adsorption-influencing parameters, including contact time, solution pH, and co-existing cations on the maximum adsorption capacity of Pb²⁺ onto the prepared composite material were investigated. Moreover, the adsorption of Pb²⁺ ions could be eliminated with rapid adsorption kinetics using the water-stable La-MOF@x%PANI composite. The as-synthesized La-MOF@50%PANI exhibited excellent adsorption performance toward Pb²⁺ ions with an extraordinary adsorption capacity of 185.19 mg/g at pH 6. The Pb²⁺ adsorption onto the La-MOF@x%PANI composite follows the pseudo-second-order kinetics and fits well with the Langmuir isotherm model, indicating the Pb²⁺ adsorption depended on the solution pH as the adsorption mechanism was mainly governed by the electrostatic attraction. Notably, La-MOF@x%PANI composite possesses outstanding regeneration ability and stability after up to four successive cycles. The satisfactory findings reflect that the La-MOF@50%PANI hybrid composite holds a great promise for remediating Pb²⁺ ions from aqueous environments.

Simultaneous immobilization of arsenic, lead and cadmium by magnesium-aluminum modified biochar in mining soil

Owing to the human activities such as smelting and mining, arsenic (As), lead (Pb) and cadmium (Cd) seriously polluted the soil of non-ferrous metal mining areas, thus efficient methods for the simultaneous immobilization of the three heavy metals are urgently needed. In the present study, Mg-Al modified biochars (MABs) were synthesized through a simple one-pot pyrolysis method to immobilize the three heavy metals. According to the BET (Brunauer-Emmett-Teller) test method, MABs had larger specific surface areas than biochar. Compared to the materials obtained at 300 °C and 700 °C, MAB with a pyrolysis temperature of 500 °C (MAB 500) had a significant immobilization effect on As, Pb and Cd in the Gansu mining area. Compared with BC, the removal efficiencies of As, Pb and Cd increased from -62%, 17% and 5% to 52%, 100% and 66%, respectively. And the toxicity characteristic leaching procedure (TCLP) test showed that the leaching concentrations of the three heavy metals in the treated soil were all lower than the standard value. X-ray photoelectron spectroscopy and kinetic experiments showed that there were various mechanisms in the immobilization process of the three heavy metals, and the large specific surface area and the multi-Mg/Al-OH of MABs play an important role in this process. More charges were provided by larger specific surface for ion exchange with heavy metals. In addition, larger specific surface area also provided more adsorption sites. More complex sites were provided by Mg/Al-OH to form Mg/Al-O-M then immobilize the heavy metals. In summary, the immobilization mechanism may involve electrostatic attraction, precipitation/co-precipitation, and surface complexation.

Preparation of structured biochar, its adsorption capacity of N and P and its characterization

Structured biochar (SC) was prepared by biochar from cattail-sludge mixture (CS) and high-density polyethylene (HDPE) and treated as an adsorbent, and the KH₂PO₄ and NH₄Cl solution were treated as adsorbates, to explore the adsorption capacity of phosphorus (P) and nitrogen (N) on SC in water. A single factor experimental method was employed to determine the optimal parameters for SC. The results showed that: 60% sizing amount, 5 N (cm²)^-1 molding pressure, 160 °C molding temperature and 95 min molding time were optimal parameters for SC preparation. The adsorption of P and N on SC conforms to the Langmuir model, with the distribution of adsorption sites on the surface tending to be even. The adsorption of P and N on SC is favorable and spontaneous, and the adsorption tends to be monolayer adsorption with a major role for chemical adsorption. The higher the temperature, the higher the adsorption capacity of P and N on SC is, and the affinity of SC with P is higher than that with N. The pseudo-second-order kinetic model for the adsorption of N and P by SC has a high degree of fit. The pH_pzc value of SC was 8.57. The hydrophobicity and stability of SC are rather high, with the surface particles closely bonded and increased roughness and pore diameter. The adsorption mechanism of P and N on SC can be attributed to pore filling, electrostatic attraction and hydrogen bonding. The results can provide a new technology for the resource utilization of cattails and sludge, a new idea for the recycling and reuse of biochar, and a basis for the selection of materials for the treatment of eutrophic water bodies.

Novel maricultural-solid-waste derived biochar for removing eutrophic nutrients and enrofloxacin: Property, mechanism, and application assessment

Land-based seawater aquaculture accompanied by high stocking density usually involves producing excess eutrophic nutrients, residual baits, excrement, and antibiotics. Because of limited technology and salinity, proper and efficient treatment of these wastes is still an unsolved issue. In this study, the feasibility of maricultural fish residual bait and excrement-derived biochar as water pollutant remover and saline-alkaline soil amendment were firstly assessed. The biochar was pyrolyzed at 300, 500, 700, 800, 900 ℃ (marked as BC300, BC500, BC700, BC800, BC900) and modified by zirconium or iron (BC700-Zr or BC700-Fe). BC700-Zr had the highest specific surface area. BC700-Zr and BC700-Fe exhibited higher nitrogen removal efficiency. The biochars exhibited nitrogen and phosphate desorption, while we observed no obvious phosphate desorption in BC700-Zr or BC700-Fe. Adsorption kinetics analysis indicated that adsorption processes of nitrate, nitrite and enrofloxacin were consistent with pseudo-second-order model, while ammonium and phosphate adsorption processes fitted pseudo-first-order model better. The biochar showed nitrogen and phosphate nutrients release effects, indicating potential application in saline-alkaline soil improvement. Multi-linear regression analysis indicated that nitrogen release was closely related to biochar nitrogen content, pH and average pore width. Phosphate release was inversely related to pH and positively related to average pore width.

Enhanced sorption of trivalent antimony by chitosan-loaded biochar in aqueous solutions: Characterization, performance and mechanisms

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

Zirconium hydroxide nanoparticle encapsulated magnetic biochar composite derived from rice residue: Application for As(III) and As(V) polluted water purification

Finding a low-cost and suitable adsorbent is still in urgent need for efficient decontamination of As(III) and As(V) elements from the polluted waters. A novel zirconium hydroxide nanoparticle encapsulated magnetic biochar composite (ZBC) derived from rice residue was synthesized for the adsorptive capture of As(III) and As(V) from aqueous solutions. The results revealed that ZBC showed an acceptable magnet separation ability and its surface was encapsulated with lots of hydrous zirconium oxide nanoparticles. Compared to As(III), the adsorption of As(V) onto ZBC was mainly dependent on the pH of the solution. The intraparticle diffusion model described the adsorption process. ZBC showed satisfactory adsorption performances to As(III) and As(V) with the highest adsorption quantity of 107.6 mg/g and 40.8 mg/g at pH 6.5 and 8.5, respectively. The adsorption of As(III) and As(V) on ZBC was almost impervious with the ionic strength while the presence of coexisting ions, especially phosphate, significantly affected the adsorption process. The processes of complexation reaction and electrostatic attraction contributed to the adsorption of As(III) and As(V) onto ZBC. ZBC prepared from kitchen rice residue was found to be a low cost environmentally friendly promising adsorbent with high removal capacity for As(III) and As(V) and could be recycled easily from contaminated waters.

Adsorption-Desorption Behavior of Arsenate Using Single and Binary Iron-Modified Biochars: Thermodynamics and Redox Transformation

Arsenic (As) is a dangerous contaminant in drinking water which displays cogent health risks to humans. Effective clean-up approaches must be developed. However, the knowledge of adsorption-desorption behavior of As on modified biochars is limited. In this study, the adsorption-desorption behavior of arsenate (As^V) by single iron (Fe) and binary zirconium-iron (Zr-Fe)-modified biosolid biochars (BSBC) was investigated. For this purpose, BSBC was modified using Fe-chips (FeBSBC), Fe-salt (FeCl₃BSBC), and Zr-Fe-salt (Zr-FeCl₃BSBC) to determine the adsorption-desorption behavior of As^V using a range of techniques. X-ray photoelectron spectroscopy results revealed the partial reduction of pentavalent As^V to the more toxic trivalent As^III form by FeCl₃BSBC and Zr-FeCl₃BSBC, which was not observed with FeBSBC. The Langmuir maximum As^V adsorption capacities were achieved as 27.4, 29.77, and 67.28 mg/g when treated with FeBSBC (at pH 5), FeCl₃BSBC (at pH 5), and Zr-FeCl₃BSBC (at pH 6), respectively, using 2 g/L biochar density and 22 ± 0.5 °C. Co-existing anions reduced the As^V removal efficiency in the order PO₄ ^3- > CO₃ ^2- > SO₄ ^2- > Cl^- > NO₃ ^-, although no significant inhibitory effects were observed with cations like Na⁺, K⁺, Mg²⁺, Ca²⁺, and Al³⁺. The positive correlation of As^V adsorption capacity with temperature demonstrated that the endothermic process and the negative value of Gibbs free energy increased (-14.95 to -12.47 kJ/mol) with increasing temperature (277 to 313 K), indicating spontaneous reactions. Desorption and regeneration showed that recycled Fe-chips, Fe-salt, and Zr-Fe-salt-coated biochars can be utilized for the effective removal of As^V up to six-repeated cycles.

Arsenic removal via a novel hydrochar from livestock waste co-activated with thiourea and γ-Fe2O3 nanoparticles

Arsenic (As) contaminants post tremendous threats to environment safety. Pristine hydrochar (PHC), thiourea-activated hydrochar (THC), and thiourea-Fe(NO₃)₃-activated hydrochar (Fe₂O₃@THC) were fabricated from dairy cattle manure via one-pot hydrothermal carbonization at 250 ℃ and applied for aqueous As(V) removal. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize hydrochars and As(V) adsorption. Thiourea increased N and S functional groups (-NH₂, C-N, C=S and S=O). Fe(NO₃)₃ introduced γ-Fe₂O₃ nanoparticles and provided Fe₂O₃@THC with Fe-O. The combination of thiourea and Fe(NO₃)₃ granted Fe₂O₃@THC with the largest surface area (33.45 m²/g), and the highest total pore volume (0.095 cm³/g) among three hydrochars. As(V) adsorption was a physicochemical process involving electrostatic attraction, complexation, ion exchange and H-bond interaction. The maximum As(V) adsorption capacities and partition coefficients decreased as follows: Fe₂O₃@THC (44.80 mg/g; 38.44 L/g) > THC (38.77 mg/g; 5.94 L/g) > PHC (19.05 mg/g; 1.17 L/g). Three hydrochars exhibited preferable reusability in NaOH solution with only 24.2%, 11.8% and 14.1% decrease in adsorption rates after four cycles for PHC, THC and Fe₂O₃@THC, respectively. Fe₂O₃@THC is a promising adsorbent for efficient As(V) removal. This study explored the efficient As(V) removal by activated hydrochars with future research potential.

Study on the Hg0 removal characteristics and synergistic mechanism of iron-based modified biochar doped with multiple metals

An iron-based composite adsorbent with biochar as the support was prepared by coprecipitation and the sol-gel method. Both single-iron-based modified biochar without doping with other metals and iron-based modified biochar doped with multiple metals (Ce, Cu, Co, Mn) were synthesised. The adsorption kinetics were analysed, and temperature-programmed desorption measurements were performed to reveal the inherent difference in mechanism between the oxidation and adsorption of Hg⁰ by the modified biochar and to elucidate the key mechanism of Hg⁰ removal. The results show that the removal of Hg⁰ by the modified biochar mainly includes adsorption and oxidation processes. The adsorption process is divided into two stages, external and internal mass transfer, both of which occur via multilayer adsorption. HgO and Hg-OM are the main forms of Hg⁰ present on the modified biochar surface. Doped metal oxides can play a synergistic role in enhancing the mercury removal performance of the modified biochar.

Antimonate sequestration from aqueous solution using zirconium, iron and zirconium-iron modified biochars

Antimony (Sb) is increasingly being recognized as an important contaminant due to its various industrial applications and mining operations. Environmental remediation approaches for Sb are still lacking, as is the understanding of Sb environmental chemistry. In this study, biosolid biochar (BSBC) was produced and utilized to remove antimonate (Sb(V)) from aqueous solution. Zirconium (Zr), Zirconium-iron (Zr-Fe) and Fe-O coated BSBC were synthesized for enhancing Sb(V) sorption capacities of BSBC. The combined results of specific surface area, FTIR, SEM-EDS, TEM-EDS, and XPS confirmed that Zr and/or Zr-Fe were successfully coated onto BSBC. The effects of reaction time, pH, initial Sb(V) concentration, adsorbate doses, ionic strength, temperature, and the influence of major competitive co-existing anions and cations on the adsorption of Sb(V) were investigated. The maximum sorption capacity of Zr-O, Zr-Fe, Zr-FeCl3, Fe-O, and FeCl3 coated BSBC were 66.67, 98.04, 85.47, 39.68, and 31.54 mg/g respectively under acidic conditions. The XPS results revealed redox transformation of Sb(V) species to Sb(III) occurred under oxic conditions, demonstrating the biochar's ability to behave as an electron shuttle during sorption. The sorption study suggests that Zr-O and Zr-O-Fe coated BSBC could perform as favourable adsorbents for mitigating Sb(V) contaminated waters.

Influence of water washing treatment on Ulva prolifera-derived biochar properties and sorption characteristics of ofloxacin

The influences of water washing treatment on the properties of Ulva prolifera-derived biochar (U.P-biochar) and its sorption characteristics of ofloxacin (OFL) were investigated. The results showed that the water washing treatment significantly changed the physiochemical structures of U.P-biochars, and improved the sorption capacity of OFL. The sorption capacity of OFL by U.P-biochar was closely dependent on pyrolysis temperature (200-600 °C) and equilibrium solution pH (3-11). Different sorption mechanisms (e.g. cation exchange, electrostatic attraction, H-bond and cationic-π and π-π interactions) were dominant for specific U.P-biochars under various pH regions (acidic, neutral and alkaline). Moreover, the unwashed and washed U.P-biochars prepared at 200 °C (BC200 and BCW200) showed a higher sorption capacity of OFL at pH = 7. The two-compartment first-order model provided an appropriate description of the sorption kinetics of OFL by BC200 and BCW200 (R2 > 0.98), which revealed that the contribution ratios between the fast and slow sorption compartments (ffast/fslow, 1.55 for BC200 and 1.25 for BCW200) reduced after water washing treatment of U.P-biochar. The values of n for the Freundlich model were less than 1, which demonstrated that the sorption of OFL by BC200 and BCW200 was favourable and nonlinear. Also, the sorption of OFL by BC200 and BCW200 increased with an increase in solution temperature and the sorption process was spontaneous and endothermic. This study provides valuable information for being a primary consideration in the production and application of U.P-biochar.

Synthesis of nano-zirconium-iron oxide supported by activated carbon composite for the removal of Sb(v) in aqueous solution

In this study, nano zirconium iron oxide based on activated carbon (ZIC) was successfully prepared by using the coprecipitation method. Compared with unmodified activated carbon, ZIC increases the number of active sites by adding metal oxides and hydroxyl groups and greatly improves the adsorption capacity of Sb(v). The synthesized nanocomposites were characterized and analysed by XRD, SEM, FT-IR, VSM and other techniques. The results showed that the zirconium iron oxide particles were successfully loaded and uniformly distributed on the surface of the activated carbon, and the agglomeration phenomenon was reduced. The saturation magnetization of ZIC was 1.89 emu g⁻¹, which easily achieved solid–liquid separation under the action of an external magnetic field. In batch experiments, when the initial concentration was 1 mg L⁻¹, the dosage of ZIC was 600 mg L⁻¹, the pH value was 5.0, the contact time was 180 min, and the removal rate of Sb(v) reached 97.82%. The maximum adsorption capacity of ZIC for Sb(v) was 11.80 mg g⁻¹. Under the interference of various inorganic ions and dissolved organics, the excellent adsorption capacity was still due to ZIC. The adsorption form was multimolecular-layer adsorption, the adsorption process was an endothermic reaction, and chemical adsorption was dominant as the adsorption mechanism. ZIC has good removal efficiency and is reusable, which indicates that ZIC has prospects for practical wastewater treatment.

The adsorbent was highly effective in the removal of Sb(v). The adsorbent easily achieved solid–liquid separation under the action of an external magnetic field.