Dissimilatory Fe(III) reduction characteristics of paddy soil extract cultures treated with glucose or fatty acids

Dissimilatory Fe(Ⅲ) reduction is a universal process with irreplaceable biological and environmental importance in anoxic environments. Our knowledge about Fe(Ⅲ) reduction predominantly comes from pure cultures of dissimilatory Fe(Ⅲ) reducing bacteria (DFRB). The objective of this study was to compare the effects of glucose and a selection of short organic acids (citrate, succinate, pyruvate, propionate, acetate, and formate) on Fe(Ⅲ) reduction via the anaerobic culture of three paddy soil solutions with Fe(OH)3 as the sole electron acceptor. The results showed significant differences in Fe(Ⅲ) reduction among the three paddy soil solutions and suhstrate types. Bacteria from the Sichuan paddy soil responded quickly to substrate supply and showed higher Fe(Ⅲ) reducing activity than the other two soil types. Bacteria in the Jiangxi paddy soil culture solution could not use propionate as a source of electrons for Fe(Ⅲ) reduction. Similarly, bacteria in the Jilin paddy soil culture could not use succinate effectively. Pyruvate was readily used by cultures from all three paddy soil solutions, thus indicating that there were some similarities in substrate utilization by bacteria for Fe(Ⅲ) reduction. The use of glucose and citrate as substrate for dissimilatory Fe(Ⅲ) reduction indicates important ecological implications for this type of anoxic respiration.     

Effect of Fe(Ⅲ) on the bromate reduction by humic substances in aqueous solution

Humic substances are ubiquitous redox-active organic compounds of environment.In this study,experiments were conducted to determine the reduction capacity of humic acid in the matrix of bromate and Fe(Ⅲ) solutions and the role of Fe(Ⅲ) in this redox process.The results showed that the humic acid regenerated Fe(Ⅱ) and reduced bromate abiotically.The addition of Fe(Ⅲ) could accelerate the bromate reduction rate by forming humic acid-Fe(Ⅲ) complexes.Iron species acts as electron mediator and catalyst for the bromate reduction by humic acid,in which humic acid transfers electrons to the complexed Fe(Ⅲ) to form Fe(Ⅱ),and the regenerated Fe(Ⅱ) donate the electrons to bromate.The kinetics study on bromate reduction further indicated that bromate reduction by humic acid-Fe(Ⅲ) complexes is pH dependent.The rate decreased by 2-fold with the increase in solution pH by one unit.The reduction capacity of Aldrich humic acid was observed to be lower than that of humic acid or natural organic matter of Suwanne River,indicating that such redox process is expected to occur in the environment.     

Simultaneous Fe(Ⅲ) reduction and ammonia oxidation process in Anammox sludge

In recent years, there have been a number of reports on the phenomenon in which ferric iron(Fe(Ⅲ)) is reduced to ferrous iron [Fe(Ⅱ)] in anaerobic environments, accompanied by simultaneous oxidation of ammonia to NO2-, NO3-, or N2.However, studies on the relevant reaction characteristics and mechanisms are rare. Recently, in research on the effect of Fe(Ⅲ) on the activity of Anammox sludge, excess ammonia oxidization has also been found.Hence, in the present study, Fe(Ⅲ) was used to serve as the electron acceptor instead of NO2-,and the feasibility and characteristics of Anammox coupled to Fe(Ⅲ) reduction(termed Feammox) were investigated. After 160 days of cultivation, the conversion rate of ammonia in the reactor was above 80%, accompanied by the production of a large amount of NO3-and a small amount of NO2-. The total nitrogen removal rate was up to 71.8%. Furthermore,quantities of Fe(Ⅱ) were detected in the sludge fluorescence in situ hybridization(FISH) and denaturated gradient gel electrophoresis(DGGE) analyses further revealed that in the sludge, some Anammox bacteria were retained, and some microbes were enriched during the acclimatization process. We thus deduced that in Anammox sludge, Fe(Ⅲ) reduction takes place together with ammonia oxidation to NO2-and NO3-along with the Anammox process.     

Bacterial reduction and release of adsorbed arsenate on Fe(Ⅲ)-, Al- and coprecipitated Fe(Ⅲ)/Al-hydroxides

Mobilization of arsenic under anaerobic conditions is of great concern in arsenic contaminated soils and sediments. Bacterial reduction of As(V) and Fe(Ⅲ) influences the cycling and partitioning of arsenic between solid and aqueous phase. We investigated the impact of bacterially mediated reductions of Fe(Ⅲ)/Al hydroxides-bound arsenic(V) and iron(Ⅲ) oxides on arsenic release. Our results suggested that As(V) reduction occurred prior to Fe(Ⅲ) reduction, and Fe(Ⅲ) reduction did not enhance the release of arsenic. Instead, Fe(Ⅲ) hydroxides retained their dissolved concentrations during the experimental process, even though the new iron mineral-magnetite formed. In contrast, the release of reduced As(Ⅲ) was promoted greatly when aluminum hydroxides was incorporated. Thus, the substitution of aluminum hydroxides may be responsible for the release of arsenic in the contaminated soils and sediments, since aluminum substitution of Fe(Ⅲ) hydroxides universally occurs under natural conditions.     

Enhanced removal of Cr(Ⅵ) by biochar with Fe as electron shuttles

Biochar is extensively used as an effective soil amendment for environmental remediation.In addition to its strong contaminant sorption capability, biochar also plays an important role in chemical transformation of contaminant due to its inherent redox-active moieties.However, the transformation efficiency of inorganic contaminants is generally very limited when the direct adsorption of contaminants on biochar is inefficient. The present study demonstrates the role of Fe ion as an electron shuttle to enhance Cr(Ⅵ) reduction by biochars. Batch experiments were conducted to examine the effects of Fe(Ⅲ) levels,pyrolysis temperature of biochar, initial solution pH, and biochar dosage on the efficiency of Cr(Ⅵ) removal. Results showed a significant enhancement in Cr(Ⅵ) reduction with an increase in Fe(Ⅲ) concentration and a decrease of initial pH. Biochar produced at higher pyrolysis temperatures(e.g., 700°C) favored Cr(Ⅵ) removal, especially in the presence of Fe(Ⅲ), while a higher biochar dosage proved unfavorable likely due to the agglomeration or precipitation of biochar. Speciation analysis of Fe and Cr elements on the surface of biochar and in the solution further confirmed the role of Fe ion as an electron shuttle between biochar and Cr(Ⅵ). The present findings provide a potential strategy for the advanced treatment of Cr(Ⅵ) at low concentrations as well as an insight into the environmental fate of Cr(Ⅵ) and other micro-pollutants in soil or aqueous compartments containing Fe and natural or engineered carbonaceous materials.     

Effect of Fe（Ⅲ） on the bromate reduction by humic substances in aqueous solution

Humic substances are ubiquitous redox-active organic compounds of environment. In this study, experiments were conducted to determine the reduction capacity of humic acid in the man-ix of bromate and Fe（Ⅲ） solutions and the role of Fe（Ⅲ） in this redox process. The results showed that the humic acid regenerated Fe（Ⅱ） and reduced bromate abiotically. The addition of Fe（Ⅲ） could accelerate the bromate reduction rate by forming humic acid-Fe（Ⅲ） complexes. Iron species acts as electron mediator and catalyst for the bromate reduction by humic acid, in which humic acid transfers electrons to the complexed Fe（Ⅲ） to form Fe（Ⅱ）, and the regenerated Fe（Ⅱ） donate the electrons to bromate. The kinetics study on bromate reduction further indicated that bromate reduction by humic acid-Fe（Ⅲ） complexes is pH dependent. The rate decreased by 2-fold with the increase in solution pH by one unit. The reduction capacity of Aldrich humic acid was observed to be lower than that of humic acid or natural organic matter of Suwanne River, indicating that such redox process is expected to occur in the environment.     

Photo-induced transformations of Hg(Ⅱ) species in the presence of Nitzschia hantzschiana,ferric ion,and humic acid

Effects of algae Nitzschia hantzschiana, Fe(Ⅲ) ions, humic acid, and pH on the photochemical reduction of Hg(Ⅱ) using the irradiation of metal halide lamps (λ 365 nm, 250 W) were investigated. The photoreduction rate of Hg(Ⅱ) was found to increase with increasing concentrations of algae, Fe(Ⅲ) ions, and humic acid. Alteration of pH value affected the photoreduction of Hg(Ⅱ) in aqueous solution with or without algae. The photoreduction rate of Hg(II) decreased with increasing initial Hg(Ⅱ) concentration in aqueous solution in the presence of algae. The photochemical kinetics of initial Hg(Ⅱ) and algae concentrations on the photoreduction of Hg(Ⅱ) were studied at pH 7.0. The study on the total Hg mass balance in terms of photochemical process revealed that more than 42% of Hg(Ⅱ) from the algal suspension was reduced to volatile metallic Hg under the conditions investigated.     

Preliminary study on the electrocatalytic performance of an iron biochar catalyst prepared from iron-enriched plants

Eichhornia crassipes is a hyperaccumulator of metals and has been widely used to remove metal pollutants from water, but disposal of contaminated plants is problematic.Biochar prepared from plants is commonly used to remediate soils and sequester carbon.Here, the catalytic activity of biochar prepared from plants enriched with iron was investigated as a potentially beneficial use of metal-contaminated plants.In a 30-day hydroponic experiment, E.crassipes was exposed to different concentrations of Fe(Ⅲ)(0, 4, 8, 16, 32 and 64 mg/L), and Fe-biochar(Fe-BC) was prepared by pyrolysis of the plant roots.The biochar was characterized using X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive X-ray spectrometry(EDS), Brunauer–Emmett–Teller(BET) analysis, X-ray photoelectron spectroscopy(XPS) and atomic absorption spectrometry(AAS).The original root morphology was visible and iron was present as γ-Fe_2O_3 and Fe_3O_4.The biochar enriched with Fe(Ⅲ) at 8 mg/L(8-Fe-BC) had the smallest specific surface area(SSA, 13.54 m~2/g) and the highest Fe content(27.9 mg/g).Fe-BC catalytic activity was tested in the electrocatalytic reduction of H_2O_2 using cyclic voltammetry(CV).The largest reduction current(1.82 mA/cm~2) was displayed by 8-Fe-BC, indicating the highest potential catalytic activity.We report here, for the first time, on the catalytic activity of biochar made from iron-enriched plants and demonstrate the potential for reusing metalcontaminated plants to produce a biochar catalyst.     

Maghemite(γ-Fe_2O_3) nanoparticles enhance dissimilatory ferrihydrite reduction by Geobacter sulfurreducens: Impacts on iron mineralogical change and bacterial interactions

Microbially mediated bioreduction of iron oxyhydroxide plays an important role in the biogeochemical cycle of iron.Geobacter sulfurreducens is a representative dissimilatory ironreducing bacterium that assembles electrically conductive pili and cytochromes.The impact of supplementation withγ-Fe_2O_3 nanoparticles(NPs)(0.2 and 0.6 g)on the G.sulfurreducens-mediated reduction of ferrihydrite was investigated.In the overall performance of microbial ferrihydrite reduction mediated byγ-Fe_2O_3 NPs,stronger reduction was observed in the presence of direct contact withγ-Fe_2O_3 NPs than with indirect contact.Compared to the production of Fe(Ⅱ)derived from biotic modification with ferrihydrite alone,increases greater than 1.6-and 1.4-fold in the production of Fe(Ⅱ)were detected in the biotic modifications in which direct contact with 0.2 g and 0.6 gγ-Fe_2O_3 NPs,respectively,occurred.X-ray diffraction analysis indicated that magnetite was a unique representative iron mineral in ferrihydrite when active G.sulfurreducens cells were in direct contact withγ-Fe_2O_3 NPs.Because of the sorption of biogenic Fe(Ⅱ)ontoγ-Fe_2O_3 NPs instead of ferrihydrite,the addition ofγ-Fe_2O_3 NPs could also contribute to increased duration of ferrihydrite reduction by preventing ferrihydrite surface passivation.Additionally,electron microscopy analysis confirmed that the direct addition ofγ-Fe_2O_3 NPs stimulated the electrically conductive pili and cytochromes to stretch,facilitating long-range electron transfer between the cells and ferrihydrite.The obtained findings provide a more comprehensive understanding of the effects of iron oxide NPs on soil biogeochemistry.     

A collaborative strategy for enhanced reduction of Cr(Ⅵ) by Fe(0) in the presence of oxalate under sunlight:Performance and mechanism

Nanometer-size zero-valent iron(NZVI) is an efficient reducing agent,but its surface is easily passivated with an oxide layer,leading to reaction inefficiency.In our study,oxalate(OA) was introduced into this heterogeneous system of NZVI,which could form ferrioxalate complexes with the NZVI surface-bound Fe~(3+) and dissolved Fe~(3+) in the solution.Photolysis of ferrioxalate complexes can facilitate the generation of Fe~(2+) from Fe~(3+)and CO_2~(·-) radical,both species have strong reduction capacity.Hence,a "photo-oxalate-Fe(0)"system through sunlight induction was established,which not only prohibited the formation of a surface passivation layer,but also displayed a synergetic mechanism of ferrioxalate photolysis to enhance reduction,exhibiting remarkably higher degradation activity(several times faster) toward the model pollutant Cr(Ⅵ) than the mechanism with NZVI alone.Factor tests suggested that both NZVI dosage and OA content markedly affected the reduction rate.Low pH was beneficial to the reduction efficiency.Moreover,recyclability experiment showed that the reduction rate decreased from 0.21706 to 0.03977 min~(-1) after three cycles of reuse due to the NZVI losing reaction activity generally,but the system still maintained considerable reduction capacity.Finally,a mechanism was revealed whereby NZVI would transform to Fe oxides after the exhaustion of its reductive power,and the photolysis of ferrioxalate to promote the cycling of iron species played the predominant role in providing extra reduction ability.These features confirm that introduction of OA into Cr(Ⅵ) reduction by NZVI through sunlight induction is advantageous and promising.     

Influence of the structure and composition of Fe–Mn binary oxides on rGO on As(Ⅲ) removal from aquifers

Fe–Mn binary oxide(FMBO) possesses high efficiency for As(Ⅲ) abatement based on the good adsorption affinity of iron oxide and the oxidizing capacity of Mn(Ⅳ), and the composition and structure of FMBO play important roles in this process.To compare the removal performance and determine the optimum formula for FMBO, magnetic graphene oxide(MRGO)–FMBO and MRGO–MnO_2 were synthesized with MRGO as a carrier to improve the dispersity of the adsorbents in aquifers and achieve magnetic recycling.Results indicated that MRGO–FMBO had higher As(Ⅲ) removal than that of MRGO–MnO_2,although the ratios of Fe and Mn were similar, because the binary oxide of Fe and Mn facilitated electron transfer from Mn(Ⅳ) to As(Ⅲ), while the separation of Mn and Fe on MRGO–MnO_2 restricted the process.The optimal stoichiometry x for MRGO–FMBO(Mn_xFe_(3-x)O_4) was 0.46, and an extraordinary adsorption capacity of 24.38 mg/g for As(Ⅲ) was achieved.MRGO–FMBO showed stable dispersive properties in aquifers, and exhibited excellent practicability and reusability, with a saturation magnetization of 7.6 emu/g and high conservation of magnetic properties after 5 cycles of regeneration and reuse.In addition, the presence of coexisting ions would not restrict the practical application of MRGO–FMBO in groundwater remediation.The redox reactions of As(Ⅲ) and Mn(Ⅳ) on MRGO–FMBO were also described.The deprotonated aqueous As(Ⅲ) on the surface of MRGO–FMBO transferred electrons to Mn(Ⅳ), and the formed As(Ⅴ) oxyanions were bound to ferric oxide as inner-sphere complexes by coordinating their "–OH" groups with Mn(Ⅳ)oxides at the surface of MRGO–FMBO.This work could provide new insights into highperformance removal of As(Ⅲ) in aquifers.     

Nanoencapsulation of hexavalent chromium with nanoscale zero-valent iron: High resolution chemical mapping of the passivation layer

Solid phase reactions of Cr(Ⅵ) with Fe(0) were investigated with spherical-aberration-corrected scanning transmission electron microscopy(Cs-STEM) integrated with X-ray energy-dispersive spectroscopy(XEDS). Near-atomic resolution elemental mappings of Cr(Ⅵ)–Fe(0) reactions were acquired. Experimental results show that rate and extent of Cr(Ⅵ) encapsulation are strongly dependent on the initial concentration of Cr(Ⅵ) in solution. Low Cr loading in nZⅥ(1.0 wt%) promotes the electrochemical oxidation and continuous corrosion of n ZⅥ while high Cr loading(1.0 wt%) can quickly shut down the Cr uptake. With the progress of iron oxidation and dissolution, elements of Cr and O counter-diffuse into the nanoparticles and accumulate in the core region at low levels of Cr(Ⅵ)(e.g., 10 mg/L). Whereas the reacted n ZⅥ is quickly coated with a newly-formed layer of 2–4 nm in the presence of concentrated Cr(Ⅵ)(e.g., 100 mg/L). The passivation structure is stable over a wide range of pH unless pH is low enough to dissolve the passivation layer. X-ray photoelectron spectroscopy(XPS) depth profiling reconfirms that the composition of the newly-formed surface layer consists of Fe(Ⅲ)–Cr(Ⅲ)(oxy)hydroxides with Cr(Ⅵ) adsorbed on the outside surface. The insoluble and insulating Fe(Ⅲ)–Cr(Ⅲ)(oxy)hydroxide layer can completely cover the n ZⅥ surface above the critical Cr loading and shield the electron transfer. Thus, the fast passivation of nZⅥ in high Cr(Ⅵ) solution is detrimental to the performance of nZⅥ for Cr(Ⅵ) treatment and remediation.     

Pilot study on bromate reduction in ozonation of water with low carbonate alkalinities by carbon dioxide

A pilot study was carried out to explore the application of carbon dioxide for pH depression in a bubble column and its ability to inhibit bromate formation for water with a low alkalinity. Results showed that in the absence of ammonia, CO2 was capable of reducing bromate 38.0%–65.4% with one-unit pH depression. CO2 caused a slightly lower bromate reduction (4.2%) than did H2SO4 when the pH was depressed to 7.4, and a more a pronounced lower reduction (8.8%) when the pH was depressed to 6.9. In the presence of 0.20 mg/L-N ammonia, bromate was largely inhibited with 73.9% reduction. When the pH was depressed to 7.4, CO2 and H2SO4 showed an 11.3% and 23.5% bromate reduction respectively, demonstrating that the joint use of CO2 and ammonia might be a plausible strategy of blocking all three bromate formation pathways. CO2 could be applied through the aeration diffuser together with ozone gas, resulting in a similar bromate reduction compared with the premixing method through Venturi mixer.     

Thiocyanate-induced labilization of schwertmannite: Impacts and mechanisms

Schwertmannite is an amorphous iron(III)-oxyhydroxysulfate that forms in acid mine drainage(AMD) environments. The characteristic of high heavy metal adsorption capability makes schwertmannite a potentially useful, environmentally friendly material in wastewater treatment. Unstable schwertmannite is prone to recrystallization.Understanding the mechanisms that induce schwertmannite labilization and affect its capacity to remove heavy metals are of great environmental and geochemical significance.Thiocyanate(SCNˉ) is a hazardous pseudohalide that is also normally found in AMD.However, little is known about the impact of Fe(III)-binding ligand SCNˉ on schwertmannite stability and its subsequent capacity to bind trace elements. Here, we investigated the adsorption of SCNˉ on schwertmannite and subsequent mineral transformation to characterize this little-known process. The appearance of Fe2+indicated that the interactions between schwertmannite and SCNˉ may involve complexation and reduction reactions. Results showed that the majority of the adsorbed-SCNˉ was immobilized on schwertmannite during the 60-days transformation. The transformation rates of schwertmannite increased with increasing concentrations of SCNˉ. Goethite was detected as the dominant transformation product with or without SCNˉ. The mechanisms of SCNˉ-promoted dissolution of schwertmannite can be described as follows:(1) formation of Fe(III)–NCS complexes on the schwertmannite surface and in solution, a process which increases the reactivity of solid phase Fe(III);(2) the extraction of Fe(III) from schwertmannite by SCNˉ and subsequent schwertmannite dissolution; and(3) the formation of secondary minerals from extracted Fe(III). These findings may improve AMD treatment strategies and provide insight into the use and potential reuse of schwertmannite as a trace element sorbent.     

On-line batch production of ferrate with an chemical method and its potential application for greywater recycling with Al(Ⅲ) salt

Ferrate(Ⅵ ) salt is an oxidant and coagulant for water and wastewater treatment. It is considered as a possible alternative method in greywater treatment. However, challenges have existed in putting ferrate(Ⅵ ) technology into full-scale practice in water and wastewater treatment due to the instability of ferrate solution and high production cost of solid ferrate products. This study demonstrated a new approach of greywater treatment with on-line batch production of Fe(Ⅵ ) to which Fe(Ⅲ ) salt was oxidized at a weak acidity solution. A series of experiments were conducted to investigate the effect of Fe(Ⅵ ) on light greywater(total organic carbon(TOC) = 19.5 mg/L) and dark greywater(TOC = 55 mg/L)treatment under different conditions with varying p H and Fe(Ⅵ ) doses. In addition, the combination use of Fe(Ⅵ ) and Al(Ⅲ ) salts was proved to be more efficient than using the Fe(Ⅵ ) salts alone at greywater recycling. The optimum dosage of Fe(Ⅵ )/Al(Ⅲ ) salts was 25/25 mg/L for light greywater, 90/60 mg/L for dark greywater, respectively. The TOC values of both light greywater and dark greywater were reduced to less than 3 mg/L with the dosages.The cost for treating greywater was 0.06–0.2 $/ton at ferrate(Ⅵ ) dosage of 25–90 mg/L and0.008–0.024 $/ton at AlCl_3 dosage of 25–60 mg/L. The full operating cost needs further assessment before the Fe(Ⅵ )/Al(Ⅲ ) technology could be implemented in greywater treatment.     

A collaborative strategy for enhanced reduction of Cr(VI) by Fe(0) in the presence of oxalate under sunlight: Performance and mechanism

Nanometer-size zero-valent iron (NZVI) is an efficient reducing agent, but its surface is easily passivated with an oxide layer, leading to reaction inefficiency. In our study, oxalate (OA) was introduced into this heterogeneous system of NZVI, which could form ferrioxalate complexes with the NZVI surface-bound Fe³⁺ and dissolved Fe³⁺ in the solution. Photolysis of ferrioxalate complexes can facilitate the generation of Fe²⁺ from Fe³⁺ and CO₂^?- radical, both species have strong reduction capacity. Hence, a “photo-oxalate-Fe(0)” system through sunlight induction was established, which not only prohibited the formation of a surface passivation layer, but also displayed a synergetic mechanism of ferrioxalate photolysis to enhance reduction, exhibiting remarkably higher degradation activity (several times faster) toward the model pollutant Cr(VI) than the mechanism with NZVI alone. Factor tests suggested that both NZVI dosage and OA content markedly affected the reduction rate. Low pH was beneficial to the reduction efficiency. Moreover, recyclability experiment showed that the reduction rate decreased from 0.21706 to 0.03977 min^?1 after three cycles of reuse due to the NZVI losing reaction activity generally, but the system still maintained considerable reduction capacity. Finally, a mechanism was revealed whereby NZVI would transform to Fe oxides after the exhaustion of its reductive power, and the photolysis of ferrioxalate to promote the cycling of iron species played the predominant role in providing extra reduction ability. These features confirm that introduction of OA into Cr(VI) reduction by NZVI through sunlight induction is advantageous and promising.     

Experimental study on Cr(Ⅵ) reduction by Pseudomonas aeruginosa

Investigation on Cr( Ⅵ ) reduction was conducted using Pseudomonas aeruginosa. The study demonstrated that the Cr(Ⅵ) canbe effectively reduced to Cr( Ⅲ ) by Pseudomonas aeruginosa. The effects of the factors affecting Cr( Ⅵ ) reduction rate including carbon source type, pH, initial Cr(Ⅵ) concentration and amount of calls inoculum were thoroughly studied. Malate was found to yield maximum biotransformation, followed by succinate and glucose, with the reduction rate of 60.86%, 43. 76% and 28.86% respectively. The optimum pH for Cr( Ⅵ ) reduction was ?.0, with reduction efficiency of 61.71 % being achieved. With the increase of initial Cr(Ⅵ) concentration,the rate of Cr(Ⅵ) reduction decreased. The reduction was inhibited strongly when the initial Cr(Ⅵ) concentration increased to 157 mg/L. As the amount of cells inoculum increased, the rate of Cr( Ⅵ ) reduction also increased. The mechanism of Cr( Ⅵ ) reduction and final products were also analysed. The results suggested that the soluble enzymes appear to be responsible for Cr (Ⅵ) reduction by Pseudomonas aeruginosa, and the reduced Cr( Ⅲ ) was not precipitated in the form of Cr(OH)3.     

Iron–doped bismuth oxybromides as visible-light-responsive Fenton catalysts for the degradation of atrazine in aqueous phases

Pesticides and its degradation products, being well–known residues in soil, have recently been detected in many water bodies as pollutants of emerging concerns, and thus there is a contemporary demand to develop viable and cost–effective techniques for the removal of related organic pollutants in aqueous phases. Herein, a visible-light-responsive Fenton system was constructed with iron–doped bismuth oxybromides(Fe–BiOBr) as the catalysts.Taking the advantage of sustainable Fe(Ⅲ)/Fe(Ⅱ) conversion...     

Role of interfacial electron transfer reactions on sulfamethoxazole degradation by reduced nontronite activating H2O2

It has been documented that organic contaminants can be degraded by hydroxyl radicals ( • OH) produced by the activation of H₂ O₂ by Fe(II)-bearing clay. However, the interfacial electron transfer reactions between structural Fe(II) and H 2 O 2 for • OH generation and its effects on contaminant remediation are unclear. In this study, we first investigated the relation between • OH generation sites and sulfamethoxazole (SMX) degradation by activating H₂O₂ using nontronite with different reduction extents. SMX (5.2–16.9 μmol/L) degradation first increased and then decreased with an increase in the reduction extent of nontronite from 22% to 62%, while the • OH production increased continually. Passivization treatment of edge sites and structural variation results revealed that interfacial electron transfer reactions between Fe(II) and H 2 O 2 occur at both the edge and basal plane. The enhancement on basal plane interfacial electron transfer reactions in a high reduction extent rNAu-2 leads to the enhancement on utilization efficiencies of structural Fe(II) and H 2 O 2 for • OH generation.However, the • OH produced at the basal planes is less efficient in oxidizing SMX than that of at edge sites. Oxidation of SMX could be sustainable in the H 2 O 2 /rNAu-2 system through chemically reduction. The results of this study show the importance role of • OH generation sites on antibiotic degradation and provide guidance and potential strategies for antibiotic degradation by Fe(II)-bearing clay minerals in H 2 O 2 -based treatments.