The degradation of decabromodiphenyl ether in the e-waste site by biochar supported nanoscale zero-valent iron /persulfate

Biochars-inlaided nano zero-valent iron reactors: A tool for visualized analysis of soil-nanomaterials micro-interfacial interaction in soil remediation process

It is a great challenge to depict the evolution process of soil-nanomaterials micro-interfaces during soil remediation. A novel biochar loaded nano zero-valent iron (BC-nZVI) reactor with low density, high reactivity and suitable magnetism was prepared using the method we established. Fe0 nanoparticles (NPs) with the size <10 nm uniformly embedded in a layer of porous carbon networks, which attached firmly in the pores and outer surface of biochars. The BC-nZVI reactors efficiently degraded and mineralized pentachlorophenol (PCP) in soil in a wide pH range within 72 h at room temperature. BC-nZVI were easily collected from soil using sieving method or floating technology followed with magnetic separation. The evolution of interfacial properties of BC-nZVI was measured using XPS, Raman spectroscopy, XRD and SEM-EDS. Even supported by BCs, aggregation and oxidation of Fe NPs inevitably took place on the outer surface of BC-nZVI in PCP remediation process. For BC-nZVIFeSO4 prepared via traditional impregnation and carbothermal method, severe agglomeration and various aging products of Fe NPs were seen in the pores as well. Due to the protection of porous carbon networks, Fe NPs aggregation was greatly mitigated in the pores of BC-nZVI and the Fe2+/Fe3+ ratio on BC-nZVI surface was still as high as the fresh one. Meanwhile, about 10-20 % of carbon matrix was oxidized and turned into amorphous carbon. The Fe NPs corrosion products, broken carbon phase, and K+ of BC-nZVI reactors were released into soil and had little effect or even enhanced the soil bacterial community diversity and biomass. However, the BC-nZVI itself showed certain adverse effect to soil microbes.

Surfactant-assisted biodegradation of nitrobenzene in groundwater by sulfided nano-zero valent iron activated persulfate: Synergistic effect, mechanism, and application

Groundwater contamination by dense non-aqueous phase liquids (DNAPLs), particularly nitrobenzene, represents a significant environmental challenge due to their chemical stability, persistence, and low solubility. This study aims to develop a synergistic approach for the biodegradation of nitrobenzene in groundwater, leveraging a combined system of Tween 80-assisted solubilization, sulfidized nano-zero valent iron (S-nZVI), and persulfate (PS) activation. The reduction process is facilitated by S-nZVI, while PS activation generates strong oxidizing radicals, and Tween 80 enhances nitrobenzene solubilization, thus improving the overall treatment efficacy. Laboratory experiments, including both batch and column studies, were conducted to evaluate the performance of this approach. Furthermore, a persulfate slow-release gel system was introduced to provide sustained activation, leading to improved long-term degradation efficiency. The results demonstrated that the synergistic combination of S-nZVI, PS, and Tween 80 led to significantly enhanced degradation of nitrobenzene and its byproduct aniline, achieving degradation rates of up to 96.74% for nitrobenzene and 100% for aniline after 6 h under optimal conditions. Additionally, the oxidation rate of aniline reached 91.53% within 5 min when the optimal dosage of 1.2 mM PS was used. The Tween-80/S-nZVI/PS slow-release gel system further achieved cumulative degradation rates of 87.49% for nitrobenzene over 14 pore volumes in a column study, demonstrating its potential for practical applications in groundwater remediation. These findings provide a promising new direction for the remediation of contaminated groundwater.

Activation of persulfate by a layered double oxide supported sulfidated nano zero-valent iron for efficient degradation of 2,2',4,4'-tetrabromodiphenyl ether in soil

The nano zero-valent iron (nZVI) activated persulfate (PS) is recognized as a promising approach to degrade 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), which is ubiquitous in the soil at electronic waste sites. However, all the reported studies were performed in liquids, gaps in the real behaviour and microbial contribution to the degradation of BDE-47 in soil media need to be urgently filled. The removal efficiency of BDE-47 is low using traditional nZVI as activator because of its aggregation and corrosion. Herein, we designed a novel layered double oxide supported sulfidated nano zero-valent iron (S-nZVI@LDO) composite and explored the performance of S-nZVI@LDO/PS to remediate BDE-47 contaminated soil. The results showed that S-nZVI@LDO has excellent stability and superior reduction capability. It could couple PS to achieve a rapid and efficient degradation of BDE-47, and the removal efficiency reached 92.31 % (5 mg/kg) within 6 h, which was much higher than that of n-ZVI/PS (53.38 %) or S-nZVI/PS (75.69 %). The kinetic constant of BDE-47 degradation by S-nZVI@LDO/PS was 23.6 and 3.7 times higher than that by single S-nZVI@LDO and nZVI/PS, respectively. It is attributable to the efficient production of SO4•-, •OH, O2•-, and 1O2 in the system, in which SO4•- and •OH dominated. The bioinformatic analysis demonstrate that soil remediation by S-nZVI@LDO/PS significantly enriched aromatic compounds-degrading bacteria and increased the abundance of hydrocarbon degradation functions. Microbial degradation may play important roles in the BDE-47 degradation and soil quality recovery. The identification of degradation pathways suggests that BDE-47 was degraded to very low-toxic products based on GHS toxicity prediction through a series process of debromination, hydroxylation, cleavage central oxygen, and ring opening, or even completely mineralized. The findings may provide significant implications for the in-situ clean-up of brominated flame retardants in contaminated soil using S-nZVI@LDO/PS Fenton-like system.

Advancements and Challenges in Nanoscale Zero-Valent Iron-Activated Persulfate Technology for the Removal of Endocrine-Disrupting Chemicals

Endocrine-disrupting chemicals are a new class of pollutants that can affect hormonal metabolic processes in animals and humans. They can enter the aquatic environment through various pathways and gradually become enriched, thus posing a serious threat to the endocrine and physiological systems of both animals and humans. Nano zero-valent iron has promising applications in endocrine disruptor removal due to its excellent reducing properties and high specific surface area. However, given the dispersed focus and fragmented results of current studies, a comprehensive review is still lacking. In this paper, it was analyzed that the types of endocrine disruptors and their emission pathways reveal the sources of these compounds. Then, the main technologies currently used for endocrine disruptor treatment are introduced, covering physical, chemical, and biological treatment methods, with a special focus on persulfate oxidation among advanced oxidation technologies. Also, the paper summarizes the various activation methods of persulfate oxidation technology and proposes the nZVI-activated persulfate technology as the most promising means of treatment. In addition, this paper reviews the research progress of different modification methods of nZVI in activating persulfate for the removal of EDCs. Finally, the discussion includes recycling studies of nZVI/PS technology and emphasizes the urgency and importance of endocrine disruptor treatment. The review of this paper provides further scientific basis and technical support for nZVI/PS technology in the field of endocrine disruptor management.

Exploring nanomaterial-modified biochar for environmental remediation applications

Environmental pollution, particularly from heavy metals and toxic elements, poses a significant threat to both human health and ecological systems. While various remediation technologies exist, there is an urgent need for cost-effective and sustainable solutions. Biochar, a carbon-rich product derived from the pyrolysis of organic matter, has emerged as a promising material for environmental remediation. However, its pristine form has limitations, such as low adsorption capacities, a relatively narrow range of pH adaptability which can limit its effectiveness in diverse environmental conditions, and a tendency to lose adsorption capacity rapidly in the presence of competing ions or organic matters. This review aims to explore the burgeoning field of nanomaterial-modified biochar, which seeks to overcome the limitations of pristine biochar. By incorporating nanomaterials, the adsorptive and reactive properties of biochar can be significantly enhanced. Such modifications, especially biochar supported with metal nanoparticles (biochar-MNPs), have shown promise in various applications, including the removal of heavy metals, organic contaminants, and other inorganic pollutants from aqueous environments, soil, and air. This review provides a comprehensive overview of the synthesis techniques, characterization methods, and applications of biochar-MNPs, as well as discusses their underlying mechanisms for contaminant removal. It also offers insights into the advantages and challenges of using nanomaterial-modified biochar for environmental remediation and suggests directions for future research.

Persulfate activation with biochar supported nanoscale zero- valent iron: Engineering application for effective degradation of NCB in soil

Nitrochlorobenzene (NCB) is very common in pesticide and chemical industries, which has become a major problem in soil environment. However, the remediation of NCB contaminated soil is received finite concern. Using biochar as a substrate for nanoscale-zero valent iron (nZVI/p-BC) to activate peroxodisulfate (PDS), a novel heterogeneous oxidative system had been applied in the current study to remediate NCB contaminants in soil. The degradation efficiencies and kinetics of m-NCB, p-NCB, and o-NCB by various systems were contrasted in soil slurry. Key factors including the dosage of nZVI/p-BC, the molar ratio of nZVI/PDS, initial pH and temperature on degradation of NCB were further examined. The results confirmed that the nZVI/p-BC/PDS displayed the remarkable performance for removing NCB compared with other systems. Higher temperature with nZVI/PDS molar ratio of 2:1 under the acidic condition favored the reduction of NCB. The treatment for NCB with optimal conditions were evaluated for the engineering application. The mechanism of nZVI/p-BC/PDS indicated that electron transfer between p-BC and nZVI was responsible for activation of PDS, generating active species (SO4•-, •OH and 1O2) via both the free and non-free radical pathways. Experimental results revealed prominent availability of nZVI/p-BC/PDS system in remediation of actual contaminated field by NCB.

Magnetic Fe-doped silicon carbide induced microwave activated persulfate for decabromodiphenyl ether removal: Mechanism and unique degradation pathway

In this work, the magnetic nanocomposite Fe@SiC was prepared by a hydrothermal method and determined by SEM, XRD, XPS, FTIR and VNA. Fe3O4 particles were loaded onto SiC with great success, and the synthesized composites had favorable microwave absorption properties. Fe@SiC was used to activate persulfate in a microwave field for the degradation of BDE209 in soil. Specifically, the synergistic interaction between microwaves and Fe@SiC showed excellent catalytic performance in activating PS to degrade BDE209 (90.1% BDE209 degradation in 15 min). The presence of •OH, O2•- and 1O2 was demonstrated based on quench trapping and EPR experiments. LC‒MS was applied to determine the intermediates and propose the possible degradation pathway for BDE209 in the MW/Fe@SiC/PS system, and it was found that BDE209 produced almost no lower brominated diphenyl ethers. Therefore, the toxicity of BDE209 was found to be reduced using toxicity assessment software. Overall, this work provides an effective approach for the degradation of BDE209 in environmental remediation.

An overview of electrokinetically enhanced chemistry technologies for organochlorine compounds (OCs) remediation from soil

In recent years, electrokinetic (EK) remediation technology has gained significant attention among researchers. This technology has proven effective in the remediation of low-permeability polluted soil. Organochlorines (OCs) are highly toxic, persistent, bioaccumulative, and capable of long-distance migration. They can also accumulate through the food chain, posing significant environmental risks. This paper provides a review of the reaction mechanism of combining chemical technology with EK remediation for the removal of several typical OCs. Furthermore, the factors influencing the efficiency of EK remediation, such as pH and ζ potential, voltage gradients, electrode materials, electrolytes, electrode arrangements, and soil types, are summarized. The paper also presents an overview of recent advancements in the methods of combining chemical technology with EK remediation for the treatment of OCs contaminated soil. Specifically, the research progress in surfactants-combined EK technology, chemical oxidation-combined EK technology, chemical reduction-combined EK technology, and chemical adsorption-combined EK technology is summarized. These findings serve as a foundation for ongoing and future research endeavors in the field. Further exploration and investigation in this area are essential for advancing the field and improving environmental remediation strategies.

Simultaneous remediation of co-contaminated soil by ball-milled zero-valent iron coupled with persulfate oxidation

The problem of co-contaminated soil at e-waste dismantling sites is serious and constitutes a critical threat to human health and the ecological environment. Zero-valent iron (ZVI) has been proven to be effective in the stabilization of heavy metals and the removal of halogenated organic compounds (HOCs) from soils. However, for the remediation of co-contamination of heavy metals with HOCs, ZVI has disadvantages such as high remediation cost and inability to take into account both pollutants, which limits its large-scale application. In this paper, boric acid and commercial zero-valent iron (cZVI) were used as raw materials to prepare boric acid-modified zero-valent iron (B-ZVI^bm) through a high-energy ball milling strategy. B-ZVI^bm coupled with persulfate (PS) to achieve simultaneous remediation of co-contaminated soil. The synergistic treatment of PS and B-ZVI^bm resulted in the removal efficiency of 81.3% for decabromodiphenyl ether (BDE209) and the stabilization efficiencies of 96.5%, 99.8%, and 28.8% for Cu, Pb, and Cd respectively in the co-contaminated soil. A series of physical and chemical characterization methods showed that the oxide coat on the surface of B-ZVI^bm could be replaced by borides during ball milling. The boride coat facilitated the exposure of the Fe⁰ core, promoted the corrosion of ZVI and the orderly release of Fe²⁺. The analysis of the morphological transformation of heavy metals in soils revealed that most of the heavy metals in the exchangeable, carbonate-bound state were transformed into the residue state, which was the key mechanism for the remediation of heavy metal-contaminated soils with B-ZVI^bm. The analysis of BDE209 degradation products showed that BDE209 was degraded to lower brominated products and further mineralized by ZVI reduction and free radical oxidation. In general, B-ZVI^bm coupled with PS is a good recipe for synergistic remediation of co-contaminated soils with heavy metals and HOCs.

Remediation of polybrominated diphenyl ethers contaminated soil in the e-waste disposal site by ball milling modified zero valent iron activated persulfate

Hydrophobic organic compounds (HOCs) in e-waste disposal sites are difficult to remove effectively. There is little reported about zero valent iron (ZVI) coupled with persulfate (PS) to achieve the removal of decabromodiphenyl ether (BDE209) from soil. In this work, we have prepared the flake submicron zero valent iron by ball milling with boric acid (B-mZVI^bm) at a low cost. Sacrifice experiments results showed that 56.6% of BDE209 was removed in 72 h with PS/B-mZVI^bm, which was 2.12 times than that of micron zero valent iron (mZVI). The morphology, crystal form, atomic valence, composition, and functional group of B-mZVI^bm were determined by SEM, XRD, XPS, and FTIR, and the results indicated that the oxide layer on the surface of mZVI is replaced by borides. The results of EPR indicated that hydroxyl radical and sulfate radical played the dominant role in the degradation of BDE209. The degradation products of BDE209 were determined by gas chromatography-mass spectrometry (GC-MS), accordingly, the possible degradation pathway was further proposed. The research suggested that ball milling with mZVI and boric acid is a low-cost means of preparing highly active zero valent iron materials. And the mZVI^bm has promising applications in improving the activation efficiency of PS and enhancing the removal of the contaminant.

Nitrogen-doped biochar (N-doped BC) and iron/nitrogen co-doped biochar (Fe/N co-doped BC) for removal of refractory organic pollutants

The presence of refractory organic pollutants (ROPs) in the ecosystem is a serious concern because of their impact on environmental constituents as well as their known or suspected ecotoxicity and adverse health effects. According to previous studies, carbonaceous materials, such as biochar (BC), have been widely used to remove pollutants from ecosystems owing to their desirable features, such as relative stability, tunable porosity, and abundant functionalities. Nitrogen (N)-doping and iron/nitrogen (Fe/N) co-doping can tailor BC properties and provide supplementary functional groups as well as extensive active sites on the N-doped and Fe/N co-doped BC surface, which is advantageous for interaction with and removal of ROPs. This review investigates the impact of N-doped and Fe/N co-doped BC on the removal of ROPs through adsorption, activation oxidation, and catalytic reduction due to the synergistic Fe, N, and BC features that modify the physicochemical properties, surface functional groups, and persistent free radicals of BC to aid in the degradation of ROPs. Owing to the attractive properties of N-doped and Fe/N co-doped BCs for the removal of ROPs, this review focuses and evaluates previous experimental investigations on the manufacturing (including precursors and influencing parameters during manufacturing) and characterizations of N-doped and Fe/N co-doped BCs. Additionally, the effective applications and mechanisms of N-doped and Fe/N co-doped BCs in adsorption, activation oxidation, and reductive remediation of ROPs are investigated herein. Moreover, the application of N-doped and Fe/N co-doped BC for progressive environmental remediation based on their effectiveness against co-pollutants, regeneration, stability, affordability, and future research prospects are discussed.

Reduction of Hexavalent Chromium from Soil of the Relocated Factory Area with Rice Straw Hydrothermal Carbon Modified by Nano Zero-Valent Iron (nZVI)

In order to reduce the content of Cr(VI) in the soil of the relocated chromium salt factory, the rice straw-derived hydrothermal carbon was prepared by hydrothermal method and loaded with nano zero-valent iron generated by liquid phase reduction, which effectively alleviated the self-aggregation problem of nano zero-valent iron (nZVI) in the treatment of Cr(VI) and improved the Cr(VI) reduction rate without changing the soil structure. The reduction effect of Cr(VI) in soil by key influencing factors such as carbon-iron ratio, initial pH value, and initial temperature was investigated. The results showed that nZVI modified hydro-thermal carbon composite (named RC-nZVI) had a good reduction effect on Cr(VI). Scanning electron microscope (SEM) and energy spectrum analysis showed that nZVI was evenly distributed on the surface of hydrothermal carbon, which effectively reduced the agglomeration of iron. Under the conditions of C/Fe = 1:2, 60 °C, with pH of 2, the average Cr(VI) content in soil decreased from 182.9 mg kg-1 to 21.6 mg kg-1. Adsorption kinetics of Cr(VI) by RC-nZVI fit well with the pseudo-second-order model, and the kinetic velocity constant revealed that Cr(VI) reduction rate decreased with increasing initial Cr(VI) concentration. Cr(VI) reduction by RC-nZVI was mainly dominated by chemical adsorption.

In situ formed CaSO4 on waste dander biochar to inhibit the mineralization of soil organic carbon

In order to reduce CO2 emissions, as well as realize the resource utilization of waste dander (WD) and the goal of international "peak carbon dioxide emissions" and "carbon neutrality", Biochar was prepared with WD via pyrolysis technology, achieving CaSO4 in situ generated on its surface, which could be used to inhibit soil organic carbon (SOC) from mineralizing and enhance soil carbon sequestration ability. The characterization results showed that the unstable carbon (C) structures as well as more conjugated structures were generated on Ca-BC, obtaining an increased C sequestration of Ca-BC to 21.70 %. With the application of Ca-BC, the mineralization rate of SOC was reduced to 0.451 mg CO2/(g·d), and the soil moisture content, pH and TOC content were increased to 45.48 %, 7.96 and 47.19 %. In addition, the bioinformatics analysis and redundancy analysis revealed that the application of Ca-BC promoted bacteria to convert into the stable C-dominant phyla (Firmicutes).

Roles of soil active constituents in the degradation of sulfamethoxazole by biochar/persulfate: Contrasting effects of iron minerals and organic matter

The biochar/persulfate (BC/PS) has been extensively applied in the degradation of organic contaminants in the aqueous solutions. However, much less work has been done on the degradation of organic contaminants in soil by BC/PS, especially on the unclear roles of soil active constituents in the degradation. This study was conducted to investigate the degradation of sulfamethoxazole (SMX) in two soils through PS oxidation activated by biochar. Biochar was produced via the pyrolysis of peanut shell at 400 °C and 700 °C, which was denoted as BC400 and BC700, respectively. Two soils used were red soil and paddy soil, mainly differing in iron minerals and organic matter. Both biochar promoted SMX degradation (42.6 %-90.7 %) in two soils, compared to PS alone (20.9 %-41.7 %). In BC400/PS system, the free radicals were the dominant reactive species for SMX degradation, while the electron transfer pathway played a vital role in the SMX degradation by BC700/PS. Higher SMX degradation was observed in red soil (41.7 %-97.8 %) than that in paddy soil (20.3 %-94.8 %), which was ascribed to the promotion of iron minerals in red soil yet the inhibition of organic matter in paddy soil. Specifically, the reaction between ≡Fe(III)/≡Fe(II) and PS on the surface of iron minerals in red soil generated more SO₄^•- and ^•OH, resulting in the enhanced SMX degradation. However, the consumption of free radicals and suppression of electron transfer pathway by organic matter in paddy soil inhibited SMX degradation. As the comparative carbonaceous materials to biochar, graphite exerted no obvious degradation effect, whereas activated carbon exhibited the comparable promoting efficacy to BC700. Both biochar, especially BC700, significantly (p < 0.05) alleviated the adverse effects of PS treatment on wheat (Triticum aestivum L.) growth. Overall, this study demonstrates that biochar/persulfate was effective in SMX degradation in soil and the degradation was affected by soil iron minerals and organic matter, which should be paid more attention in the persulfate remediation of organic contaminated soils at a specific site.

Catalytic degradation of brominated flame retardants in the environment: New techniques and research highlights

Due to the extensive commercial use of brominated flame retardants (BFRs), human beings are chronically exposed to BFRs, causing great harms to human health, which imposes urgent demands to degrade them in the environment. Among various degradation techniques, catalytic degradation has been proven to be outstanding because of its rapidness and effectiveness. Therefore, much attention has been given to catalytic degradation, especially the extensively studied photocatalytic degradation and nanocatalytic reduction techniques. Recently, some novel advanced catalytic techniques have been developed and show excellent catalytic degradation efficiency for BFRs, including natural substances catalytic degradation, new Fenton catalytic degradation, new chemical reagent catalytic degradation, new material catalytic degradation, electrocatalytic degradation, plasma catalytic degradation, and composite catalytic degradation systems. In addition to the common features of traditional catalytic techniques, these novel techniques possess their own specific advantages in various aspects. Therefore, this review summarized the degradation mechanism of BFRs by the above new catalytic degradation methods under the laboratory conditions, simulated real environment, and real environment conditions, and further evaluated their advantages and disadvantages, aiming to provide some research ideas for the catalytic degradation of BFRs in the environment in the future. We suggested that more attention should focus on features of novel catalytic techniques, including eco-friendliness, cost-effectiveness, and pragmatic usefulness.

Application of persulfate-based oxidation processes to address diverse sustainability challenges: A critical review

Over the past years, persulfate (PS) is widely applied due to their high versatility and efficacy in decontamination and sterilization. While treatment of organic chemicals, remediation of soil and groundwater, sludge treatment, disinfection on pathogen microorganisms have been covered by most published reviews, there are no comprehensive and specific reviews on its application to address diverse sustainability challenges, including solid waste treatment, resources recovery and regeneration of ecomaterials. PS applications mainly rely on direct oxidation by PS itself or the reactive sulfate radical (SO₄^•-) or hydroxyl radical (^•OH) from the activation of peroxodisulfate (PDS, S₂O₈^2-) or peroxymonosulfate (PMS, HSO₅^-) in SO₄^•--based advanced oxidation processes (SO₄^•--AOPs). From a broader perspective of environmental cleanup and sustainability, this review summarizes the various applications of PS except pollutant decontamination and elaborates the possible reaction mechanisms. Additionally, the differences between PS treatment and conventional technologies are highlighted. Challenges, research needs and future prospect are thus discussed to promote the development of the applications of PS-based oxidation processes in niche environmental fields. In all, this review is a call to pay more attention to the possibilities of PS application in practical resource reutilization and environmental protection except widely reported pollutant degradation.

Applications and influencing factors of the biochar-persulfate based advanced oxidation processes for the remediation of groundwater and soil contaminated with organic compounds

Biochar (BC) is a low-cost material rich in carbon, which is being used increasingly as a catalyst in persulfate-based advanced oxidation processes (PS-AOPs) for the remediation of groundwater and soil contaminated with organic compounds. In this work, a general summary of preparation methods and applications of various BC (i.e., pristine BC, magnetic BC, and chemically modified BC) in PS-AOPs is presented. Different influence factors (e.g., pH, anions, natural organic matter) for the degradation of organic compounds are discussed. Meanwhile, the influence of external energy (e.g., solar irradiation, UV-Vis, ultrasonic) is also mentioned. Furthermore, the advantage of different BC in PS-AOPs are compared. Finally, potential problems, challenges, and prospects in the application of biochar-persulfate based advanced oxidation processes (BCPS-AOPs) are discussed in the conclusion and perspective.

Direct 3D printing of zero valent iron@polylactic acid catalyst for tetracycline degradation with magnetically inducing active persulfate

Catalyst stability has become a challenging issue for advanced oxidation processes (AOPs). Herein, we report an alternative method based on 3D printing technology to obtain zero-valent iron polylactic acid prototypes (ZVI@PLA) in a single step and without post etching treatment. ZVI@PLA was used to activate persulfate (PS) for the removal of Tetracycline (TC) in recirculating mode under two different heating methodologies, thermal bath and contactless heating promoted by magnetic induction (MIH). The effect of both heating methodologies was systematically analysed by comparing the kinetic constant of the degradation processes. It was demonstrated that the non-contact heating of ZVI by MIH reactivates the surface of the catalyst, renewing the surface iron content exposed to the pollutant solution, which makes the ZVI@PLA catalyst reusable up to 10 cycles with no efficiency reduction. In contrast, by using a conventional thermal bath, the kinetic constant gradually decreases over the 10 cycles, because of the superficial iron consumption, being the kinetic constant 5 times lower in the 10th run compared to MIH experiment. X-ray diffraction and Mössbauer spectroscopy confirmed the presence of metallic iron embedded in the ZVI@PLA prototype, whose crystalline structure remained unchanged for 10th cycles of MIH. Moreover, it was proven that with no contact heating technology at low magnetic fields (12.2 mT), the solution temperature does not increase, but only the surface of the catalyst does. Under these superficial heated conditions, kinetic rate is increased up to 0.016 min^-1 compared to the value of 0.0086 min^-1 obtained for conventional heating at 20 °C. This increase is explained not only by PS activation by iron leaching but also by the contribution of ZVI in the heterogeneous activation of persulfate.

Highly efficient debromination of 4,4'-dibrominated diphenyl ether by organic palygorskite-supported Pd/Fe nanoparticles

Organic palygorskite (OP)-supported Pd/Fe nanoparticles composite (OP-Pd/Fe) was prepared by stepwise reduction method. The removal capacity of 4,4'-dibrominated diphenyl ether (BDE15) by OP-Pd/Fe was compared with other various materials. For better understanding the possible mechanism, the synthesized and reacted OP-Pd/Fe materials were characterized by TEM, SEM, XRD, and XPS, respectively. The effects of major influencing parameters on the degradation of BDE15 were also studied. Benefit from the synergistic effect of the carrier and bimetallic nanoparticles, BDE15 could be completely debrominated into diphenyl ether (DE) under suitable conditions. A two-stage adsorption/debromination removal mechanism was proposed. The degradation of BDE15 with OP-Pd/Fe was mainly stepwise debromination reaction, and hydrogen transfer mode was assumed as the dominated debromination mechanism. The removal process fitted well to the pseudo first-order kinetic equation. The observed rate constants increased with increasing Pd loading and OP-Pd/Fe dosage while decreased with increasing initial BDE15 concentration, the tetrahydrofuran/water ratio, and the initial pH of the solution. The work provides a new approach for the treatment of PBDEs pollution.

Highly efficient remediation of decabromodiphenyl ether-contaminated soil using mechanochemistry in the presence of additive and its mechanism

Mechanochemistry has been proved to be an effective method to remediation of organic-contaminated sites. However, the high ball-to-powder mass ratio (C_R) limits the large-scale application of mechanochemistry. In this study, co-milling additives were introduced to enhance the mechanochemical degradation of decabromodiphenyl ether (BDE209)-contaminated soil under the condition of low C_R. Based on additive screening experiments, sodium borohydride was selected as the ideal additive to assist the mechanochemical degradation of BDE209, and the resulting removal efficiency was approximately 100% with 2 h of ball milling at a rotational speed of 550 rpm. The main degradation intermediates and degradation pathway of BDE209 were identified using gas chromatography-tandem mass spectrometry. It was proposed that the degradation of BDE209 by sodium borohydride-assisted mechanochemistry was a concurrent process of stepwise and multistage debromination. Meanwhile, the meta-bromine atom in BDE209 was more susceptible to debromination than those at the para and ortho positions. The evolution of the concentration of Br^- was monitored by ion chromatography, which revealed that reduction and oxidation both occurred in the removal of BDE209. This paper provides a new perspective for reducing the C_R in the mechanochemical remediation of BDE209-contaminated soil.

Highly effective removal of bisphenol A by greigite/persulfate in spiked soil: Heterogeneous soil/water system balance and degradation

The degradation of bisphenol A (BPA) in spiked soil was studied to investigate persulfate (PS) activation by the environment-friendly heterogeneous material greigite for removing organic pollutants from soil. The effects of the PS and greigite doses were investigated, and the BPA degradation rate in the lateritic red soil was lower than that in kaolin. Notably, 500 mg/kg of BPA could be effectively removed by the flower-like greigite (FLG)/PS system in 30 min. The difference in BPA degradation in kaolin and the lateritic red soil was negligible, thus indicating that the contents of components such as total organic matters in the lateritic red soil did not affect the BPA degradation rate of the FLG/PS system considerably. Furthermore, the distribution processes of BPA in the soil and liquid phase were also investigated in detail. The results showed that the water contents were a key factor in the distribution and degradation of BPA. The transfer of BPA from kaolin to the liquid phase was simpler than that from the lateritic red soil to the liquid phase. BPA might be transferred to the liquid phase first and then degraded by the FLG/PS system in that phase. Regarding BPA degradation in the lateritic red soil, BPA was degraded in the soil and liquid phases at the same time. This study proposed a pathway for BPA degradation in soil slurries by heterogeneous material/PS systems for first time, providing a deeper understanding of the degradation mechanism of organic pollutants in soil and new methods for soil remediation.

Activation of persulfate by green nano-zero-valent iron-loaded biochar for the removal of p-nitrophenol: Performance, mechanism and variables effects

In this study, with the green tea extraction solution as a reducing agent and green tea residues as a raw material of biochar, green nano zero-valent iron biochar (G-nZVI-BC) was prepared with the green synthesis method and then combined with potassium persulfate to degrade p-nitrophenol in water. Compared with zero-valent iron-loaded biochar (C-nZVI-BC) prepared by the traditional chemical liquid phase synthesis method, G-nZVI-BC containing tea polyphenols further improved dispersibility of Fe⁰ on biochar, prevented nZVI agglomeration on BC, and promoted PNP degradation. The system constructed by G-nZVI-BC/PDS showed the high oxidation resistance than the C-nZVI-BC/PDS system, thus endowing the synthesis material with long-term reactivity. Both the radical pathway and non-radical pathways contributed to catalytic degradation and free radicals played a key role. The G-nZVI-BC/PDS system realized the good removal effect on PNP in the pH range of 3.06-9.23. The reusability of G-nZVI-BC and the PNP removal effect in water body conditions indicated that G-nZVI-BC had a good application prospect in the field of water treatment.

Synthesis of zero-valent iron/biochar by carbothermal reduction from wood waste and iron mud for removing rhodamine B

This study proposes a new process to synthesize zero-valent iron/biochar (Fe⁰-BC) by carbothermal reduction using wood waste and iron mud as raw materials under different temperature. The characterization results showed that the Fe⁰-BC synthesized at 1200 °C (Fe⁰-BC-1200) possessed favorable adsorption capacity with the specific surface area of 103.18 m²/g and that the zero-valent iron (Fe⁰) particles were uniformly dispersed on the biochar surface. The removal efficiency of rhodamine B (RB) was determined to evaluate the performance of the prepared Fe⁰-BC. Fe⁰-BC-1200 presented the best performance on RB removal, which mainly ascribes to that more Fe⁰ particles generated at higher temperature. The equilibrium adsorption capacity reached 49.93 mg/g when the initial RB concentration and the Fe⁰-BC-1200 dosage were 100 mg/L and 2 g/L, respectively, and the pseudo-second-order model was suitable to fit the removal experimental data. LCMC and XRD analyses revealed that the removal mechanism included the physical adsorption of biochar and the redox reaction of Fe⁰. Moreover, copper existing in the iron mud was also reduced to Cu⁰, which was beneficial to catalyze the oxidation of iron; the degradation of RB was promoted at the same time.

Preparation and application of Fe/biochar (Fe-BC) catalysts in wastewater treatment: A review

The removal of organic pollutants from water environments is a challenging problem. Fe-based BC (Fe-BC) composites are promising catalysts for generating reactive oxygen species (ROS) for environmental remediation considering their low costs and excellent physicochemical surface characteristics. The synthesis methods, properties, applications, and the mechanism of Fe-BC for removing pollutants are reviewed. Various methods have been used to prepare Fe-BC composites, and the synthetic methods and conditions used affect the properties of the Fe-BC material, thereby influencing its pollutant removal performance. The mechanisms of pollutant removal by Fe-BC are intricate and include adsorption, degradation and reduction. Fe loading on BC could improve the performance of BC by affecting its surface area, surface functional groups and electron transfer rate. Moreover, research gaps and uncertainties that exist in the use of Fe-BC were identified. Finally, the problems that need to be solved to make Fe-BC suitable for future applications are described.

Improvement of karst soil nutrients by arbuscular mycorrhizal fungi through promoting nutrient release from the litter

How arbuscular mycorrhizal (AM) fungi affect litter nutrient release and soil properties in the nutrient-deficient karst soil, is unclear. An experiment was conducted in this study using a dual compartment device composed of a planting compartment (for the Cinnamomum camphora seedlings with or without Funneliformis mosseae fungus) and a litter compartment (with or without the litter of Arthraxon hispidus). The center baffle between the compartments was covered with a double layer of 20-µm or 0.45-µm nylon mesh, which controlled the entrance of AM mycelium into the litter compartment. The results are as follows: AM mycelium significantly increased the mass loss and carbon and nitrogen releases and decreased the nitrogen concentration in the litter. AM mycelium could significantly increase soil organic carbon, total nitrogen and availability of phosphorus during litter decomposition in the litter compartment. Redundancy analysis showed that the effect of AM mycelium on the soil organic carbon, total nitrogen in the litter compartment was closely associated with the increase in carbon and nitrogen release from litter. It was concluded that AM mycelium can enhance litter decomposition and nutrient releases, contributing to greater nutrient input to the soil and then subsequently higher soil organic carbon and nutrient content in the nutrient-poor karst soils. STATEMENT OF NOVELTYThis study firstly estimated the impacts of arbuscular mycorrhizal fungi on litter nutrient releases and soil properties through root external mycelium.

Chlortetracycline hydrochloride removal by different biochar/Fe composites: A comparative study

In the last years, the synthesis and applications of biochar/Fe composites have been extensively studied, but only few papers have systematically evaluated their removal performances. Herein, we successfully synthesized and structurally characterized Fe⁰, Fe₃C, and Fe₃O₄-coated biochars (BCs) for the removal of chlortetracycline hydrochloride (CH). Evaluation of their removal rate and affinity revealed that Fe⁰@BC could achieve better and faster CH removal and degradation than Fe₃C@BC and Fe₃O₄@BC. The removal rate was controlled by the O-Fe content and solution pH after the reaction. The CH adsorption occurred on the O C groups of Fe⁰@BC and the OC and OFe groups of Fe₃C@BC and Fe₃O₄@BC. Electron paramagnetic resonance analysis and radical quenching experiments indicated that HO and ¹O₂/ O₂^- were mainly responsible for CH degradation by biochar/Fe composites. Additional parameters, such as effects of initial concentrations and coexisting anions, regeneration capacity, cost and actual wastewater treatment were also explored. Principal component analysis was applied for a comprehensive and quantitative assessment of the three materials, indicating Fe⁰@BC is the most beneficial functional material for CH removal.

Preparation of biochar and biochar composites and their application in a Fenton-like process for wastewater decontamination: A review

Biochar is a carbon-rich material that can be obtained from pyrolysis of solid waste (e.g., agricultural solid waste and sludge from wastewater treatment plants). Biochar features low cost, large specific surface area, and strong adsorption capacity. New biochar composites can be produced via modification and loading of nano particles onto biochar. Biochar can contribute to the dispersion and stabilization of nano particles. In addition, nano particles can increase the number of surface-active sites, which improves the physicochemical properties of the material. Biochar and biochar composites have been applied widely in wastewater treatment, and have significantly enhanced the treatment performance of Fenton-like processes (activation of hydrogen peroxide and persulfate) as an advanced oxidation process for organics removal and wastewater decontamination. This paper reviews the preparation methods for biochar and biochar composites to systematically analyze the influential factors on the preparation process. The paper also comprehensively reviews the mechanisms by which biochar removes different organic pollutants. However, due to the vast number of different biochar feedstocks and their preparation methods, it is difficult to compare the properties of one biochar to another. Guidance if provided for the application of biochar and biochar composites for wastewater decontamination.

FeS2 assisted degradation of atrazine by bentonite-supported nZVI coupling with hydrogen peroxide process in water: Performance and mechanism

In this study, bentonite-supported nZVI (B-nZVI) was used as a catalyst to activate H₂O₂ for atrazine (ATZ) degradation in the presence of FeS₂. Results indicated that ATZ degradation by B-nZVI/H₂O₂ process was significantly enhanced when FeS₂ was introduced, and nearly 98% of ATZ was degraded by B-nZVI/FeS₂/H₂O₂ process within 60 min under the optimum conditions. ATZ degradation of B-nZVI/FeS₂/H₂O₂ process was much higher than the sum of B-nZVI and FeS₂/H₂O₂ processes. The presence of HCO₃^-, PO₄^3- and F^- exhibited significant negative effects on the ATZ degradation, whereas both Cu²⁺ and Ni²⁺ exhibited positive effects on that. Both citric acid (CA) and ethylenediaminetetraacetic acid (EDTA) with lower concentration enhanced ATZ degradation rate, but significant suppression effects on that with higher concentration. The degradation of ATZ and 2,4-Dichlorophenol (2,4-DCP) could be simultaneously achieved in B-nZVI/FeS₂/H₂O₂ process under certain conditions. High soluble Fe²⁺ induced an excellent decomposition of H₂O₂ by B-nZVI and FeS₂. OH was dominant radical, and contributed to nearly 86% of the overall ATZ removal. A total of five intermediate products of ATZ were identified, and ATZ degradation was achieved via de-alkylation and hydroxylation processes. An enhanced reaction mechanism for ATZ degradation by B-nZVI/FeS₂/H₂O₂ process was proposed, and B-nZVI/FeS₂/H₂O₂ process exhibited an excellect catalytic performance within four successive runs.

One-step fabrication of oxygen vacancy-enriched Fe@Ti/C composite for highly efficient degradation of organic pollutants through persulfate activation

In this work, cost-effective, magnetic carbon-supported Fe@Ti composite (Fe@Ti/Cs) with abundant active sites was synthesized by one-step carbothermal reduction of ilmenite with the assistance of microwave oven and utilized as a highly efficient persulfate (PS) activator for the wastewater purification. The coexistence of Fe^0/2+/3+, Ti^3+/4+ and oxygen vacancies on Fe@Ti/Cs was found to favor for the electron transfer to PS, which facilitate the generation of reactive oxygen species (ROS). Catalytic experiment results showed that the Fe@Ti/C-4 produced from ilmenite/carbon with a mass ratio of 4:1 exhibited the best catalytic activation performance towards PS for the degradation of Rhodamine B (RhB). Usage of merely 0.12 g/L Fe@Ti/C-4 enabled the removal of 94.01% RhB (200 mg/L) within 30 min in the PS containing system, significantly outperforming ilmenite + PS (29.29%) and carbon + PS (49.91%) systems tested under the same conditions. The physico-chemical properties of the produced Fe@Ti/Cs before and after the reaction were carefully characterized. Radical scavenging experiments and electron paramagnetic resonance (EPR) analysis were carried out to better understand the underlying mechanism. The results indicate that oxygen vacancies in Fe@Ti/C-4 promoted the electron transfer and participated in the transition metal redox cycle to generate ROS in the PS-containing system, which was highly efficient for degrading RhB into small molecules and finally enabling mineralization. This work offers a new perspective for designing highly efficient and stable PS activators with long life derived from natural ore for environmental remediation.

Remediation of hexavalent chromium in column by green synthesized nanoscale zero-valent iron/nickel: Factors, migration model and numerical simulation

In this work, green tea extracts synthesized nanoscale zero-valent iron/nickel (GT-nZVI/Ni) was prepared and the Cr(VI) contaminated soil column was remediated by GT-nZVI/Ni suspension. The influence factors including the concentration, pH value and flow rate of GT-nZVI/Ni suspension were studied. Under the conditions of pH = 4, concentration of 0.15 g/L and flow rate of 1.25 mL/h, GT-nZVI/Ni suspension had the best reduction and immobilization effect on Cr(VI) in the soil column. Na⁺ and Ca²⁺ can promote the immobilization of Cr (VI) in soil, while humic acid weakened the immobilization of Cr (VI). After GT-nZVI/Ni is injected into the soil column, the content of weak acid extractable and reduced chromium is significantly reduced, and the toxic hazard of hexavalent chromium in the soil is greatly reduced. The 1D-CDE model was used to fit the breakthrough curves of Fe(tot), Fe(aq) and Fe(0), and the migration of GT-nZVI/Ni in Cr(VI) contaminated soil was simulated and predicted. Compared with the inert solute Cl^-, the breakthrough curves of Fe (tot), Fe (aq) and Fe (0) in Cr (VI) contaminated soil column were significantly lagged, with delay coefficients of 2.465, 2.322 and 3.288, respectively. The reaction of GT-nZVI/Ni with Cr (VI) led to the decrease of Fe mobility. Finally, the outflow concentration of Fe (tot) was 0.064 g/L, and the loss was mainly due to reaction and retention in the soil. About 57.89% of GT-nZVI/Ni was retained in the soil.

In situ chemical oxidation of contaminated groundwater using a sulfidized nanoscale zerovalent iron-persulfate system: Insights from a box-type study

We report the potential of a sulfidized nanoscale zerovalent iron-persulfate (S-nZVI-PS) system for in situ chemical oxidation (ISCO) of groundwater pollutants. The study was conducted using a sand-filled rectangular box with a permeable reactive barrier of S-nZVI as a facsimile of the ISCO system. Synthetic water contaminated with a target pollutant (reactive black-5, RB-5) was continuously passed through the box. The injection of PS led to the complete removal of RB-5 and the system remained reactive for approximately 12 days. This system has a benefit that the oxidation products of S-nZVI (i.e., Fe₃O₄, Fe₂O_3, and FeSO₄) can further activate PS to retain its reactivity. In a separate trial, this method exploited oxidation, reduction, adsorption and co-precipitation mechanisms that conspired to remove two different groundwater pollutants- arsenite and 1,4-dioxane. These results confirmed the utility of S-nZVI-PS as a mediator of ISCO processes to degrade groundwater pollutants.

Study on influencing factors and mechanism of removal of Cr(VI) from soil suspended liquid by bentonite-supported nanoscale zero-valent iron

In order to clarify the mechanism and effect of bentonite-supported nanoscale zero-valent iron (nZVI@Bent) on Cr(VI) removal in soil suspended liquid, nZVI@Bent was prepared by liquid-phase reduction method in this research. A number of factors, including the mass ratio of Fe²⁺ to bentonite during preparation of nZVI@Bent, nZVI@Bent dosage, soil suspended liquid pH value and reaction temperature were assessed to determine their impact on the reduction of Cr(VI) in soil suspended liquid. The nZVI@Bent was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to analyze the mechanism of removal of Cr(VI) from the soil. The results showed that the temperature of soil suspended liquid had a significant effect on the removal efficiency. Calculated by the Arrhenius formula, nZVI@Bent removes Cr(VI) from the soil suspended liquid as an endothermic reaction with a reaction activation energy of 47.02 kJ/mol, showed that the reaction occurred easily. The removal of mechanism Cr(VI) from the soil by nZVI@Bent included adsorption and reduction, moreover, the reduction process can be divided into direct reduction and indirect reduction. According to XPS spectrogram analysis, the content of Cr(III) in the reaction product was 2.1 times of Cr(VI), indicated that the reduction effect was greater than the adsorption effect in the process of Cr(VI) removal. The experiment proved that nZVI@Bent can effectively remove Cr(VI) from soil suspension, and can provide technical support for repairing Cr(VI)-polluted paddy fields.

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.

Polyethylene glycol-stabilized nano zero-valent iron supported by biochar for highly efficient removal of Cr(VI)

In this study, polyethylene glycol (PEG)-stabilized nano zero-valent iron (nZVI) supported by biochar (BC) (PEG-nZVI@BC) was prepared to remedy Cr(VI) with high efficiency. The morphology, functional groups, and crystalline structure of PEG-nZVI@BC composites were characterized, revealing that when PEG was added, a large number of -OH functional groups were introduced, and nZVI was effectively dispersed on the BC surface with a smaller particle size. The results of Cr(VI) remediation experiments showed Cr(VI) removal rate by PEG-nZVI@BC (97.38%) was much greater than that by BC-loaded nZVI (nZVI@BC) (51.73%). The pseudo second-order and Sips isotherm models provide the best simulation for Cr(VI) removal experimental data, respectively. The main remediation mechanism of Cr(VI) was reduction and co-precipitation of Cr-containing metal deposits onto PEG-nZVI@BC. Ecotoxicity assessment revealed PEG-nZVI@BC (1.00 g/L) has little influence on rice germination and growth, but resisted the toxicity of Cr(VI) to rice. The modified Community Bureau of Reference (BCR) sequential extraction showed pyrolysis could increase the percentage of oxidizable and residual Cr and diminish the environmental risk of Cr release from post-removal composites.