Nanoscale zero-valent iron/biochar composite as an activator for Fenton-like removal of sulfamethazine

Degradation of BTEXS with stable and pH-insensitive iron-manganese modified biochar from post pyrolysis

An efficient iron-manganese modified biochar (FMBC) was successfully synthesized as a heterogeneous Fenton-like catalyst through easy post-modification and applied for degradation of benzene, toluene, ethylbenzene, xylene isomers (ortho, para, and meta), and styrene (BTEXS) in the presence of H₂O₂. The catalyst was characterized by Brunauer-Emmett-Teller method, scanning electron microscopy, and X-ray photoelectron spectrometry. The effects of H₂O₂ concentration, FMBC dose, and initial pH on BTEXS degradation were also investigated. Results showed that degradation efficiency of FMBC for individual BTEXS varied from 83.05% to 94.12% in 3 h. Kinetic analysis showed that a first-order kinetic model with respect to BTEXS concentration could be used to explain the BTEXS degradation for FMBC/H₂O₂ system. The degradation reaction was more suitable in a wide pH range (3-10) than those in previous studies, thereby overcoming the low-efficiency problem of conventional Fenton reaction at high pH. Moreover, the doses of FMBC and H₂O₂ are a crucial factor affecting BTEXS degradation. Radical scavenger experiments revealed that ∙OH, ∙O₂^-, and ¹O₂ participated in the degradation process, and ∙OH was the major contributor. The synthesized catalyst is durable with stable BTEXS removal efficiency after seven consecutive cycles. The removal efficiency of BTEXS by FMBC in produced water reached 93.23% in 12 h, indicating FMBC has practical value.

Nano zero-valent iron on activated carbon cloth support as Fenton-like catalyst for efficient color and COD removal from melanoidin wastewater

To reduce undesired iron leaching in Fenton reaction and to realize reusability of catalyst, chitosan-coated activated carbon cloth support loaded with nano zero-valent iron (ACC-CH-nZVI) was applied as a heterogeneous Fenton catalyst to treat melanoidin wastewater. Chitosan coating on ACC by chemical crosslinking results in 6% chitosan on ACC subsequently loading 3.5% iron. At optimum conditions, ACC-CH-nZVI leads to 88.4% and 76.2% of color and chemical oxygen demand (COD) removal, respectively, upon treating synthetic melanoidin wastewater of 8000 mg/l COD. The corresponding weight ratio of consumed H₂O₂ to COD is 1.02, far below the stoichiometric ratio 2.125, indicating the economic value of this catalyst. Reusability of ACC-CH-nZVI is demonstrated for five cycles of treatment with minimal iron leaching (<2%). The high removal efficiency and very low levels of iron leaching suggests that ACC-CH-nZVI is a highly efficient and cost-effective catalyst for Fenton-like oxidation of non-biodegradable organic wastes in water.

Activation of persulfate by nanoscale zero-valent iron loaded porous graphitized biochar for the removal of 17β-estradiol: Synthesis, performance and mechanism

In this work, the porosity, graphitization and iron doping of biochar were realized simultaneously by the pyrolysis of biomass and potassium ferrate (K₂FeO₄), then the iron-doped graphitized biochar was reduced to synthesize nanoscale zero-valent iron loaded porous graphitized biochar (nZVI/PGBC). 17β-estradiol (E2) is an environmental endocrine disruptor that can cause great harm to the environment in small doses. Experiments illustrated that nZVI/PGBC (100 mg/L) could completely remove E2 (3 mg/L) within 45 min by activating sodium persulfate (PS, 400 mg/L). The E2 removal efficiency of nZVI/PGBC was obviously superior to that of pristine biochar (BC), iron-doped graphitized biochar (Fe/GBC), nanoscale zero-valent iron (nZVI) and porous graphitized biochar (PGBC). The removal efficiency could be affected by reaction conditions, including reaction temperature, acidity, dosage of catalyst and oxidant and water matrix. Quenching experiments and electron spin resonance (ESR) demonstrated that SO₄^-· and HO were both responsible for E2 degradation. This study indicated that Fe⁰ and Fe²⁺ were the main catalytic active substances, while the catalytic ability of PGBC was not obvious. The reaction mechanism was proposed, that is, PS was activated by electrons provided by the redox reaction between Fe²⁺ and Fe³⁺, and PGBC acted as the carrier of nZVI, the adsorbent of E2 and the mediator of electron-transfer. This study demonstrates that nZVI/PGBC can be used as an effective activator for PS to remove organic pollutants in water.

Self-Assembled Nano-Fe3C Embedded in Reduced Graphene Oxide Aerogel with Efficient Fenton-Like Catalysis

Aiming at the removal of refractory organic pollutants in aqueous solution, self-assembled nano-Fe3C embedded in reduced graphene oxide (nano-Fe3C@RGO) aerogel was prepared by hydrothermal synthesis and high temperature treatment, and characterized by SEM, HRTEM, pore size distribution, XRD, XPS and FTIR. The results showed that the aerogel was porous, and most of the Fe3C particles were less than 100 nm in size. They were evenly dispersed and embedded in the RGO aerogel. Furthermore, the mapping images confirmed that the elements of carbon, nitrogen and iron were homogeneously distributed. Moreover, the specific surface area of the aerogel was up to 324.770 m2/g and most of the pore sizes were between 5 and 10 nm. The formation of nano-Fe3C was identified by XRD pattern and HRTEM. Analysis of an XPS spectrum indicates that the nano-Fe3C was embedded in the graphene layer. The aerogel contained a large number of functional groups, including -NH2-NH and -C=O, etc., which greatly strengthened the adsorption of organics. Finally, the Fenton-like catalytic degradation properties of the self-assembled nano-Fe3C@RGO aerogel were investigated by testing the removal of methyl orange from the aqueous solution. The results showed that the value of Ct/C0 decreased to 0.050 after 240 min, suggesting a high degradation rate was obtained. Meanwhile, the chemical reaction was verified in accordance with the first-order kinetic model, and the higher temperature was beneficial to the catalytic degradation. At the same time, methyl orange was degraded into small molecules by the hydroxyl and superoxide radicals generated during the reactions. Therefore, the self-assembled nano-Fe3C@RGO aerogel, as a novel Fenton-like catalyst, introduces a new approach in the field of treatment of refractory organic wastewater.

A heterogeneous fenton-like system with green iron nanoparticles for the removal of bisphenol A：Performance, kinetics and transformation mechanism

Green synthesized iron nanoparticles have been received increasing attention due to its advantages of a simple, rapid and cost-effective synthesis. In this study, green iron nanoparticles by grape seed extracts (GS-Fe-NPs) were used as a heterogeneous catalyst of Fenton-like system to degrade bisphenol A (BPA) in the aqueous solution. The properties of GS-Fe-NPs before and after reaction were characterized by Scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction respectively. Effect factors, including initial pH value, initial BPA concentration, GS-Fe-NPs dosage, H₂O₂ dose and temperature on the degradation were investigated systematically. Good performances on the BPA degradation were observed over the wider pH range (3.0-11.0) in the GS-Fe-NPs/H₂O₂ system. At solution initial pH 6.9 (not adjusted), the BPA degradation efficiency could achieve 96.4% with GS-Fe-NPs 0.30 g/L and H₂O₂ 1.0 mol/L at 308 K. Furthermore, quenching experiments confirmed that OH was the main free radical and its contribution to the BPA degradation varied with the initial pH. The kinetics behavior of BPA degradation had good agreements with the pseudo-first-order model (R₁² 0.9710-0.9997), suggesting that the degradation of BPA is dominated by redox process. Based on the identified intermediates by liquid chromatography/mass spectrometry, the possible degradation pathways and BPA removal mechanism in the GS-Fe-NPs/H₂O₂ system were proposed. It provides a simple and effective water treatment method for BPA contaminated water.

Application of biochar in advanced oxidation processes: supportive, adsorptive, and catalytic role

The advanced oxidation processes (AOPs), especially sulphate radical (SO₄^•-)-based AOPs (SR-AOPs), have been considered more effective, selective, and prominent technologies for the removal of highly toxic emerging contaminants (ECs) due to wide operational pH range and relatively higher oxidation potential (2.5-3.1 V). Recently, biochar (BC)-based composite materials have been introduced in AOPs due to the dual benefits of adsorption and catalytic degradation, but the scientific review of BC-based catalysts for the generation of reactive oxygen species (ROSs) through radical- and non-radical-oriented routes for EC removal was rarely reported. The chemical treatments, such as acid/base treatment, chemical oxidation, surfactant incorporation, and coating and impregnation of minerals, were applied to make BC suitable as supporting materials (SMs) for the loading of Fenton catalysts to boost up peroxymonosulphate/persulphate/H₂O₂ activation to get ROSs including ^•OH, SO₄^•-, ¹O₂, and O₂^•- for targeted pollutant degradation. In this review, all the possible merits of BC-based catalysts including supportive, adsorptive, and catalytic role are summarised along with the possible route for the development prospects of BC properties. The limitations of SR-AOPs especially on production of non-desired oxyanions, as well as disinfection intermediates and their potential solutions, have been identified. Lastly, the knowledge gap and future-oriented research needs are highlighted.

Application of zero-valent iron coupled with biochar for removal of perfluoroalkyl carboxylic and sulfonic acids from water under ambient environmental conditions

Advanced oxidation and reduction processes have been intensively investigated as potential methods to promote the decomposition of perfluoroalkyl substances (PFASs). However, extreme operational conditions such as highly acidic pH, high temperature, and high pressure are required to promote degradation reactions, which makes these technologies costly and less feasible for full-scale applications. The objective of this study was to evaluate the effectiveness of zero-valent iron (ZVI) alone and a mixture of ZVI and biochar (ZVI + BC) for removal of seven target PFASs from water under ambient environmental conditions. Target PFASs included three perfluoroalkyl carboxylic acids (PFCAs) [perfluorooctanoic acid (PFOA, C8-PFCA), perfluoroheptanoic acid (C7-PFCA), and perfluorohexanoic acid (C6-PFCA)] and four perfluoroalkyl sulfonic acids (PFSAs) [perfluorooctane sulfonic acid (PFOS, C8-PFSA), perfluoroheptane sulfonic acid (C7-PFSA), perfluorohexane sulfonic acid (C6-PFSA), and perfluorobutane sulfonic acid (C4-PFSA)]. Batch test results show that PFSAs (up to 94% removal) were more effectively removed than PFCAs (up to 60% removal) when utilizing either ZVI or (ZVI + BC). About 20-60% of input PFOA (~18,550 μg L^-1) and 90-94% of input PFOS (~18,580 μg L^-1) were removed by ZVI alone or the mixture of (ZVI + BC). The removal efficiencies of PFCAs and PFSAs by reactive media increased with increasing chain length, from 0 to 17% for short-chain PFCAs (C6-C7) and 20 to 70% for short-chain PFSAs (C4-C7). About 5-10% of input PFOA and PFOS was partially defluorinated by ZVI alone as indicated by F^- release; however, the defluorination efficiency may be underestimated due to the sorption of F^- by the reactive media. Overall, the reactive mixture (ZVI + BC) may be an effective and environmentally sustainable material for removing PFASs from water under ambient environmental conditions.

Aging of zero-valent iron-based nanoparticles in aqueous environment and the consequent effects on their reactivity and toxicity

A fundamental understanding of the long-term fate of nanoscale zero-valent iron (nZVI)-based particles in aqueous environment and the corresponding impacts on their reactivity and toxicity is essential for the responsible use and management of the nanoparticles in environmental applications. This paper comprehensively reviews the physicochemical transformations of nZVI-based particles and the consequent effects on the particle's reactivity and toxicity. The corrosions of nZVI in water under both anaerobic and aerobic conditions are summarized. The transformation of contaminant-bearing nZVI is also discussed. Besides, the factors influencing the transformation of nZVI (i.e., pH, typical anions and cations, natural organic matter, surface stabilizers, bimetal decoration, and sulfidation treatment) are summarized and discussed. In addition, the effects of particle aging on its reactivity and toxicity are discussed. Generally, the aging of nZVI-based particles would have negative impact on the removal of contaminants, especially for the degradation of organic pollutants. However, the aging process of nZVI-based particles would cause a significant reduction in their toxicity. It is suggested that the nZVI-based particles would finally transform to less toxic or benign materials (i.e., iron (oxyhydr)oxides) over time. Finally, future perspectives are proposed to better quantify and predict the transformation of nZVI-based particles in aqueous environment. PRACTITIONER POINTS: The corrosion rates and products of nZVI in water varied much under anaerobic and aerobic conditions. Typical anions and cations, natural organic matter, and iron types are critical factors influencing the physicochemical transformation of nZVI. The aging of nZVI would have negative impact its reactivity, especially for the degradation of organic pollutants. Although the fresh nZVI exhibits obvious toxicity, the aging process would cause a significant reduction in its toxicity.

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.

Glucose enhanced the oxidation performance of iron-manganese binary oxides: Structure and mechanism of removing tetracycline

In this work, iron-manganese binary oxides (FMO) modified with different proportions of glucose addition (FMOCx) by co-precipitation method showed good activity in activating hydrogen peroxide (H₂O₂) for tetracycline degradation. The structure and surface characterizations of the FMO and FMOCx were measured by XRD, FTIR, TEM, BET and XPS. With increased glucose addition, FMOCx has more surface functional groups such as -OH and -COOH, particle size decreases, surface area gradually increases, and the ratio of high valence iron and manganese also increases. In addition, the glucose might be oxidized by KMnO₄ to form amorphous carbon on the catalyst surface. Glucose modified iron-manganese binary oxides FMOC3 (with 0.003 mol glucose added) showed the highest efficiency removal capability for tetracycline up to 85%, which attribute to it has a larger surface area, more surface functional groups and higher surface active Mn(IV) site content. The results also demonstrated that FMOC3 could efficiently activate hydrogen peroxide. This study proves that glucose modified iron-manganese binary oxides (FMOCx) can offered a possibility of degradation of refractory organic pollutants as an environmentally friendly catalyst in the absence of H₂O₂ or not.

Effective removal of two fluoroquinolone antibiotics by PEG-4000 stabilized nanoscale zero-valent iron supported onto zeolite (PZ-NZVI)

In this work, nanoscale zero-valent iron (NZVI) was synthesized via liquid phase reduction method with surfactant polyethylene glycol (PEG-4000) modified and supported onto zeolite to prepare PZ-NZVI composite. SEM-EDS, XPS, BET.etc. characterizations indicated that the sphere NZVI particles were loaded on the zeolite successfully and the aggregation was restrained. The adsorption performance of PZ-NZVI for norfloxacin (NOR) or ofloxacin (OFL), two typical fluoroquinolones (FQs), from water was conducted. The equilibrium studies were demonstrated using Langmuir, Freundlich, Temkin and Elovich isotherms and better agreement was attained with the Temkin model. Compared with NZVI and zeolite, PZ-NZVI had higher FQs removal efficiency, and the Langmuir maximum adsorption capacity was 54.67 mg g^-1 (NOR) and 48.88 mg g^-1 (OFL). The kinetic parameters displayed that two FQs adsorption onto PZ-NZVI followed pseudo-second-order kinetic model. The thermodynamic analysis suggested the adsorption process was spontaneous and exothermic. In addition, the adsorption tests were executed at different influence factors and the adsorbent PZ-NZVI was suitable for a wide pH range (4-10) with the FQs (10 mg L^-1) removal efficiency above 90% in 1 h. Furthermore, it was found that PZ-NZVI can be effortlessly separated from mixed solutions using external magnetic field. Finally, the process of FQs adsorbed onto PZ-NZVI was attributed to the surface complexion (forming bidentate complexes), hydrophobic interaction, pore filling and electrostatic interaction.

Assessment of biochar and/or nano zero-valent iron for the stabilisation of Zn, Pb and Cd: A temporal study of solid phase geochemistry under changing soil conditions

The remediation of a soil contaminated with Zn, Pb and Cd was tested by using biochar (BC), nano zero-valent iron (nZVI) and a combination of these two (BC + nZVI). Each amendment was individually applied to the soil at 2 wt%. We tested the influence of (i) the used amendments, (ii) time, and (iii) soil moisture conditions on the metal availability and soil physico-chemical parameters using various extraction methods, as well as soil pore water samplings. We found that metal availability was mainly affected by pH under the influence of time and water content. Among the tested treatments, BC was the most successful, resulting in the lowest amounts of the target metals in the pore water and the smallest temporal changes in metal concentrations and pH in the soil. The use of nZVI efficiently decreased water-extractable Pb in the short- and long-term. The BC + nZVI treatment also yielded promising results regarding the immobilisation of the studied metals. Time provoked a general decrease in pH, which occasionally increased the available metal concentrations. Raising the soil water content increased the pH and subsequently lowered the available metal concentrations in the pore water. The mechanisms of metal stabilisation were further investigated by SEM/EDS. The results indicated that the used soil amendments enhanced the binding of Zn, Pb, and Cd on Fe/Mn/Al oxides/hydroxides, which in turn resulted in the stabilisation of the target metals.

Synergistic construction of green tea biochar supported nZVI for immobilization of lead in soil: A mechanistic investigation

Biochar-based nanocomposites with functional materials provide an excellent prospect in reactivity and stability. Most biochar reported have no reusability upon aging and offer the risk of release of immobilized components after short-term immobilization. To overcome this, we developed nano zero-valent iron (nZVI) impregnated magnetic green tea biochar (nZVI@GTBC) and studied its performance in immobilizing Pb and long-term effectiveness in the soil. The reactive nZVI units were obtained from iron oxide solution by reducing with polyphenol solution (green tea extract) and were successively stabilized by impregnation onto the remaining green tea waste matrix through co-precipitation technique. Finally, the magnetic biochar was developed from the above nZVI impregnated green tea waste through oven drying and slow pyrolysis technique in different temperature range (150-650 °C). The synthesized nZVI@GTBC biochar was characterized and studied by XRD, FTIR, Raman, UV-Vis, TG/DSC, XPS, SEM, and TEM. The nZVI@GTBC obtained with a particle size of 130 nm and surface charge of +2.8 C/m² at 450 °C. Moreover, colloidal stability and mobility experiments were considered to explain the transport behavior and stability of bare nZVI and magnetic nZVI@GTBC in the soil. The immobilization of Pb by pristine nZVI, GTBC, and nZVI@GTBC was compared and explained under different soil pH conditions. The bioavailability of Pb content before and after immobilization was investigated through leaching experiments. Further, thirty days of soil incubation were carried out to examine different species of Pb according to the Tessier sequential extraction scheme. The study suggested that nZVI@GTBC enhanced the immobilization efficiency by 19.38% in comparison with pristine nZVI and 57.14% in comparison with bare GTBC biochar.

Influence of humic acid and its different molecular weight fractions on sedimentation of nanoscale zero-valent iron

The effects of humic acid (HA) and its different molecular weight (MW) fractions on the sedimentation of nanoscale zero-valent iron (NZVI) in the absence and presence of cations (i.e., Na⁺/Mg²⁺/Ca²⁺) were investigated. Ultrafiltration (UF) was used as the method of fractionation to obtain four different MW fractions (separated by ultrafiltration membranes of 10 kDa, 50 kDa, and 100 kDa). Differing sedimentation behavior was observed for NZVI with different MW fractions of HA. Generally, the degree of settling of NZVI particles in the presence of high MW fractions of HA was lower than that of low MW fractions of HA and that without HA. The results were mainly attributed to the steric stabilization provided by the high MW fractions of HA. The presence of Na⁺/Mg²⁺/Ca²⁺ alone had insignificant influence on the settling of NZVI, but both Mg²⁺ and Ca²⁺ exerted an obvious influence on the settling of NZVI in the co-presence of HA. The settling behavior of NZVI was further examined in the co-presence of different MW fractions of HA and Ca²⁺. The co-presence of low MW HA fractions and Ca²⁺ led to a lower settling of NZVI. This might be due to the formation of a layer of HA-Ca²⁺ complex on the particle surface, providing stronger steric stabilization. Nevertheless, in the co-presence of high MW HA fractions and Ca²⁺, the settling of NZVI was initially reduced but accelerated with time, which might be due to the gradual aggregation of NZVI with time resulted from the bridging effect of HA-Ca²⁺ complex.

Experimental and theoretical aspects of biochar-supported nanoscale zero-valent iron activating H2O2 for ciprofloxacin removal from aqueous solution

Ciprofloxacin has been frequently detected in water environment, and its removal has become a significant public concern. Biochar-supported nanoscale zero-valent iron (BC/nZVI) to activate hydrogen peroxide (H₂O₂) has many advantages on promoting the removal of organic contaminants. In this paper, the BC/nZVI activating H₂O₂ degradation of ciprofloxacin was systematically investigated by experimental and theoretical approaches. The morphologies and property analysis showed that nZVI particles distributed uniformly on the biochar surface, which mainly include ^-OH, >CO and COC and CO groups. Different reaction conditions were compared to define the optimal conditions for ciprofloxacin removal in BC/nZVI/H₂O₂ system. More than 70% of ciprofloxacin was removed in the optimal conditions: acidic condition (pH 3∼4), low doses of H₂O₂ (20 mM), and temperature of 298 K. The hydroxyl radical (^•OH) oxidation was the primary pathway in BC/nZVI/H₂O₂ degradation of ciprofloxacin process. The theoretical calculation indicated that hydrogen atom abstraction (HAA) pathways were the dominant oxidation pathways contributing 92.3% in overall second‒order rate constants (k) of ^•OH and ciprofloxacin. The current results are valuable to evaluate the application of BC/nZVI activating H₂O₂ degradation of ciprofloxacin and other fluoroquinolone antibiotics in water treatment plants.

Biochar-Supported FeS/Fe3O4 Composite for Catalyzed Fenton-Type Degradation of Ciprofloxacin

The Fenton-type oxidation catalyzed by iron minerals is a cost-efficient and environment-friendly technology for the degradation of organic pollutants in water, but their catalytic activity needs to be enhanced. In this work, a novel biochar-supported composite containing both iron sulfide and iron oxide was prepared, and used for catalytic degradation of the antibiotic ciprofloxacin through Fenton-type reactions. Dispersion of FeS/Fe3O4 nanoparticles was observed with scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). Formation of ferrous sulfide (FeS) and magnetite (Fe3O4) in the composite was validated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Ciprofloxacin (initial concentration = 20 mg/L) was completely degraded within 45 min in the system catalyzed by this biochar-supported magnetic composite at a dosage of 1.0 g/L. Hydroxyl radicals (·OH) were proved to be the major reactive species contributing to the degradation reaction. The biochar increased the production of ·OH, but decreased the consumption of H2O2, and helped transform Fe3+ into Fe2+, according to the comparison studies using the unsupported FeS/Fe3O4 as the catalyst. All the three biochars prepared by pyrolysis at different temperatures (400, 500 and 600 °C) were capable for enhancing the reactivity of the iron compound catalyst.

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

Biochar supported nano zero-valent iron (BC-nZVI) synthesized through liquid phase reduction method was used to activate persulfate (PS) for the removal of decabromodiphenyl ether (BDE209) in the soil. The morphology, structure and composition of BC-nZVI were determined by SEM, XRD, XPS and FTIR. Batch experiments were carried out to investigate the effect of different factors, such as the molar ratio of PS to BC-nZVI, pH value of PS solution and reaction temperature, on the degradation efficiency of BDE209. Results showed that when the molar ratio of PS/BC-nZVI was 3:1, pH value was 3, reaction temperature was 40 °C, 82.06% of BDE209 could be removed within 240 min. The process fitted pseudo-first-order kinetics model well and the apparent activation energy (Ea) was 48.92 kJ mol^-1, indicating that the process was controlled by surface reaction. The quenching experiments showed that ·SO₄^- was predominate radical species in the degradation process in acid and neutral condition. However, ·OH played more important role in alkaline condition. GC-MS was used to determine the reaction products for inferring the degradation pathway of BDE209 in soil by BC-nZVI/PS system.

Influence of feedstocks and modification methods on biochar's capacity to activate hydrogen peroxide for tetracycline removal

Three types of raw biochar (i.e. CBC, OBC, PBC produced from cornstalk, orange peel and peanut hull, respectively) and the modified ones (i.e., KMnO₄-, KOH- and H₃PO₄-treatment) were employed to activate H₂O₂ for the removal of tetracycline (TC). The effects of pyrolysis temperatures, H₂O₂ concentration and initial pH were examined. TC removal by raw biochars w/o H₂O₂ was dependent on the feedstock and pyrolysis temperature of biochar, but the removal efficiency was still quite low under optimum conditions. The KMnO₄-treatment significantly enhanced the adsorption of TC on all three biochars, but only enhanced the TC removal by CBC + H₂O₂. The KOH-treatment had insignificant effect on the adsorption of TC on biochar, but improved the performance of CBC/PBC + H₂O₂. The H₃PO₄-treatment had a negative impact on TC removal by biochar w/o H₂O₂. Overall, H₂O₂ could either enhance or decrease the TC removal by biochar, depending on biochar type, H₂O₂ concentration and solution pH.

Removal of Phenol from Steel Plant Wastewater in Three Dimensional Electrochemical (TDE) Process using CoFe2O4@AC/H2O2

This study investigated the removal of phenol from steel industry wastewater by three dimensional electrochemical (TDE) process using CoFe2O4 nanobiocomposite based activated carbon in the presence of H2O2 (EC-CoFe2O4@AC-H2O2). In this study, CoFe2O4 nanobiocomposite-foundation activated carbon (CoFe2O4@AC) was used as microelectrode, adsorbent, and activator for peroxide hydrogen. The removal efficiency of phenol and COD was investigated through the parameters of pH, contact time, CoFe2O4@AC dosage, current density, and H2O2 concentration. The highest removal rates of phenol and COD were >99% and 98%, respectively. Also, steel plant wastewater under the optimal conditions of pH = 6.5, current density = 15 mA cm−2, contact time = 25 min, H2O2 concentration of 1.0 mM, and CoFe2O4@AC dose = 0.3 g L−1. Kinetic analysis revealed that the adsorption experimental data was best fitted by the pseudo-first-order model.

Effects of different scrap iron as anode in Fe-C micro-electrolysis system for textile wastewater degradation

The degradation of organic contaminants in actual textile wastewater was carried out by iron carbon (Fe-C) micro-electrolysis. Different Fe-C micro-electrolysis systems (SIPA and SISA) were established by using scrap iron particle (SIP) and scrap iron shaving (SIS) as anode materials. The optimal condition of both systems was obtained at the initial pH of 3.0, dosage of 30 g/L and Fe/C mass ratio of 1:1. Commercial spherical Fe-C micro-electrolysis material (SFC) was used for comparison under the same condition. The results indicated that total organic carbon (TOC) and chroma removal efficiencies of SIPA and SISA were superior to that of SFC. Total iron concentration in solution and XRD analysis of electrode materials revealed that the former showed relatively high iron corrosion intensity and the physicochemical properties of scrap iron indeed affected the treatment capability. The UV-vis and 3DEEM analysis suggested that the pollutants degradation was mainly attributed to the combination of reduction and oxidation. Furthermore, the potential degradation pathways of actual textile wastewater were illustrated through the GC-MS analysis. Massive dyes, aliphatic acids, and textile auxiliaries were effectively degraded, and the SIPA and SISA exhibited higher performance on the degradation of benzene ring and dechlorination than that by SFC. In addition, SIPA and SISA exhibited high stability and excellent reusability at low cost. Graphical abstract.

Biochar-supported nZVI (nZVI/BC) for contaminant removal from soil and water: A critical review

The promising characteristics of nanoscale zero-valent iron (nZVI) have not been fully exploited owing to intrinsic limitations. Carbon-enriched biochar (BC) has been widely used to overcome the limitations of nZVI and improve its reaction with environmental pollutants. This work reviews the preparation of nZVI/BC nanocomposites; the effects of BC as a supporting matrix on the nZVI crystallite size, dispersion, and oxidation and electron transfer capacity; and its interaction mechanisms with contaminants. The literature review suggests that the properties and preparation conditions of BC (e.g., pore structure, functional groups, feedstock composition, and pyrogenic temperature) play important roles in the manipulation of nZVI properties. This review discusses the interactions of nZVI/BC composites with heavy metals, nitrates, and organic compounds in soil and water. Overall, BC contributes to the removal of contaminants because it can attenuate contaminants on the surface of nZVI/BC; it also enhances electron transfer from nZVI to target contaminants owing to its good electrical conductivity and improves the crystallite size and dispersion of nZVI. This review is intended to provide insights into methods of optimizing nZVI/BC synthesis and maximizing the efficiency of nZVI in environmental cleanup.

Removal of chloramphenicol in aqueous solutions by modified humic acid loaded with nanoscale zero-valent iron particles

As a natural organic carbon skeleton, humic acid (HA) was loaded with nanoscale zero-valent iron (nZVI) Particles to remove chloramphenicol (CAP) from aqueous solution. The pore morphology and structure, the type, the distribution and valence state of element, and the class of functional groups on the surface of the material were shown by SEM/EDS, XPS, BET and FTIR. When the load ratio of nZVI on HA was 1:30, the iron content in the material was minimized, the specific gravity of the economic material-HA was increased, and the removal efficiency of CAP was 80.0% or higher. In addition, the mass ratio of nZVI on HA, the dosage of nZVI/HA-30, the initial pH and CAP concentration of the solution, these four general factors, played an important role in the efficiency and equilibrium time of the CAP removal. The removal efficiency of CAP by nZVI/HA-30 was 84.2% when the dosage was 1.0 g (100 mL)^-1, the initial concentration of CAP was 30 mg L^-1 and the pH was 3. The reaction pathway and removal mechanism of ZVI/HA-30 were studied by the concentration of total and ferrous iron ions in the solution, UV-Vis and MS. The CAP was continuously denitrified and dechlorinated, decomposed into easily degradable substances by nZVI particles supported on HA, which was consistent with the first-order kinetic model within 5 min. This newly synthesized material was economical and efficient, easy to store, effectively prevented agglomeration and passivation of nZVI, and had a good application prospect for removing contaminants from water.

Toxicity of sulfide-modified nanoscale zero-valent iron to Escherichia coli in aqueous solutions

Sulfide-modified nanoscale zero-valent iron (S/nZVI) has been widely studied for groundwater remediation, but the potential environmental risks are poorly understood. This study examined the toxicity of S/nZVI to Escherichia coli in aqueous solutions. The sulfidation could reduce toxicity of nZVI, and S/nZVI exhibited a weaker toxicity at lower Fe/S molar ratio, resulting from the lower Fe⁰ content and higher sulfate and iron oxide. The toxicity of S/nZVI was significantly alleviated in the presence of N-Acetyl-L-cysteine (a scavenger for reactive oxygen species (ROS)), revealing that the ROS-induced oxidative stress was the principal mechanism. Moreover, Transmission Electron Microscopy images elucidated that the membranes of S/nZVI-treated cells were disrupted and S/nZVI existed on E. coli surface and in the cytoplasm. S/nZVI might have interacted with the amine, carboxyl, and ester groups on E. coli cell surface, as demonstrated by Fourier Transform Infrared Spectroscopy analysis. However, the presence of individual groundwater component (e.g., Ca²⁺, SO₄^2-, HCO₃^- and humic acid) could more or less alleviate the toxicity of S/nZVI. Furthermore, S/nZVI only exhibited slight toxic effect (<0.15-log after 1 h) in the presence of the mixed components. The same faint toxicity was observed for the aged S/nZVI, indicating that S/nZVI could lose its toxicity over time.

Integration of nanoscale zero-valent iron and functional anaerobic bacteria for groundwater remediation: A review

The technology of integrating nanoscale zero-valent iron (nZVI) and functional anaerobic bacteria has broad prospects for groundwater remediation. This review focuses on the interactions between nZVI and three kinds of functional anaerobic bacteria: organohalide-respiring bacteria (OHRB), sulfate reducing bacteria (SRB) and iron reducing bacteria (IRB), which are commonly used in the anaerobic bioremediation. The coupling effects of nZVI and the functional bacteria on the contaminant removal in the integrated system are summarized. Generally, nZVI could create a suitable living condition for the growth and activity of anaerobic bacteria. OHRB and SRB could synergistically degrade organic halides and remove heavy metals with nZVI, and IRB could reactive the passivated nZVI by reducing the iron (hydr)oxides on the surface of nZVI. Moreover, the roles of these anaerobic bacteria in contaminant removal coupling with nZVI and the degradation mechanisms are illustrated. In addition, this review also discusses the main factors influencing the removal efficiency of contaminants in the integrated treatment system, including nZVI species and dosage, inorganic ions, organic matters, pH, type of pollutants, temperature, and carbon/energy sources, etc. Among these factors, the nZVI species and dosage play a fundamental role due to the potential cytotoxicity of nZVI, which might exert a negative impact on the performance of this integrated system. Lastly, the future research needs are proposed to better understand this integrated technology and effectively apply it in groundwater remediation.

Synergistic degradation of PNP via coupling H2O2 with persulfate catalyzed by nano zero valent iron

Simultaneous activation of H₂O₂ and persulfate by nanoscaled Fe⁰ shows synergistic effect for degradation of p-nitrophenol with generating both hydroxyl and sulfate radicals in a wide initial pH range.

Effective Degradation of Rh 6G Using Montmorillonite-Supported Nano Zero-Valent Iron under Microwave Treatment

Nano zero-valent iron has drawn great attention for the degradation of organic dyes due to its high reactivity, large specific surface area, lightweight, and magnetism. However, the aggregation and passivation of iron nanoparticles may prohibit the wide use of it. A new composite material was prepared by loading nano zero-valent iron (nZVI) on montmorillonite (MMT) to overcome the above shortcomings and it was further used for the removal of Rhodamine 6G (Rh 6G) under microwave treatment in the present work. The effects of various parameters, including the initial concentration of Rh 6G, microwave power, and pH value were investigated. The new composite material (nZVI/MMT) showed an excellent degradation ability for removing Rh 6G, and the removal amount reached 500 mg/g within 15 min. The degradation rate reached 0.4365 min⁻¹, significantly higher than most previous reports using other removal methods for Rh 6G.