The redox state of arsenic controls its toxicity and mobility in the subsurface environment. Understanding the redox reactions of arsenic is particularly important for addressing its environmental behavior. Clay miner...The redox state of arsenic controls its toxicity and mobility in the subsurface environment. Understanding the redox reactions of arsenic is particularly important for addressing its environmental behavior. Clay minerals are commonly found in soils and sediments, which are an important host for arsenic. However, limited information is known about the redox reactions between arsenic and structural Fe in clay minerals. In this study, the redox reactions between As(Ⅲ)/As(Ⅴ) and structural Fe in nontronite NAu-2 were investigated in anaerobic batch experiments. No oxidation of As(Ⅲ) was observed by the native Fe(Ⅲ)-NAu-2. Interestingly, anaerobic oxidation of As(Ⅲ) to As(Ⅴ) occurred after Fe(Ⅲ)-NAu-2 was bioreduced. Furthermore, anaerobic oxidization of As(Ⅲ) by bioreduced NAu-2 was significantly promoted by increasing Fe(Ⅲ)-NAu-2 reduction extent and initial As(Ⅲ) concentrations. Bioreduction of Fe(Ⅲ)-NAu-2 generated reactive Fe(Ⅲ)-O-Fe(Ⅱ) moieties at clay mineral edge sites. Anaerobic oxidation of As(Ⅲ) was attributed to the strong oxidation activity of the structural Fe(Ⅲ) within the Fe(Ⅲ)-O-Fe(Ⅱ) moieties. Our results provide a potential explanation for the presence of As(Ⅴ) in the anaerobic subsurface environment. Our findings also highlight that clay minerals can play an important role in controlling the redox state of arsenic in the natural environment.展开更多
It has been documented that organic contaminants can be degraded by hydroxyl radicals(•OH)produced by the activation of H2O2 by Fe(II)-bearing clay.However,the interfacial electron transfer reactions between structura...It has been documented that organic contaminants can be degraded by hydroxyl radicals(•OH)produced by the activation of H2O2 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(5.2–16.9μmol/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 H2O2 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 H2O2-based treatments.展开更多
The mineralogical and micromorphological characteristics of Si-Fe-Mn oxyhydroxides from the dacite-hosted PACMANUS hydrothermal field were analyzed.The samples are poorly crystallized Si-Fe-Mn oxyhydroxides with minor...The mineralogical and micromorphological characteristics of Si-Fe-Mn oxyhydroxides from the dacite-hosted PACMANUS hydrothermal field were analyzed.The samples are poorly crystallized Si-Fe-Mn oxyhydroxides with minor birnessite, todorokite, nontronite, goethite, and opal-A.There are some microtextures which are rather like fossil microbes such as the filamentous silica and the hollow pipes.Flakes of nontronite crystals are found either forming a honeycomb texture or distrib- uted on the surface of the hollow pipes.Nontronite is the product precipitated from low-temperature hydrothermal fluids, and microbes may play a role in its formation.Si-Fe-Mn oxyhydroxides have two kinds of nuclei: Si-Mn nuclei and Si nuclei, both enveloped by the similar Si-Fe outer layer, existing in the rod-shaped oxyhydroxide and spheroidal oxyhydroxide, respectively.In the Si-Mn nuclei, the concentration of SiO2 is between 39.32 wt% and 86.31 wt%, and MnO concentration is between 4.97 wt% and 27.01 wt%, but Fe2O3 concentration is very low (0.54 wt%-3.43 wt%).In the Si nucleus the concentration of SiO2 is 90.17 wt%, but concentration of MnO and Fe2O3 are low, with 0.06 wt% and 3.47 wt%, respectively.The formation of the Si-Mn nucleus is closely related to microbes, whereas the Si nucleus is of inorganic origin.展开更多
基金supported by the National Natural Science Foundation of China(Nos.41977280,51678557,U1904205,and 51808541)the special fund from Key Laboratory of Drinking Water Science and Technology,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences(Nos.15Z09KLDWST and 18Z03KLDWST)。
文摘The redox state of arsenic controls its toxicity and mobility in the subsurface environment. Understanding the redox reactions of arsenic is particularly important for addressing its environmental behavior. Clay minerals are commonly found in soils and sediments, which are an important host for arsenic. However, limited information is known about the redox reactions between arsenic and structural Fe in clay minerals. In this study, the redox reactions between As(Ⅲ)/As(Ⅴ) and structural Fe in nontronite NAu-2 were investigated in anaerobic batch experiments. No oxidation of As(Ⅲ) was observed by the native Fe(Ⅲ)-NAu-2. Interestingly, anaerobic oxidation of As(Ⅲ) to As(Ⅴ) occurred after Fe(Ⅲ)-NAu-2 was bioreduced. Furthermore, anaerobic oxidization of As(Ⅲ) by bioreduced NAu-2 was significantly promoted by increasing Fe(Ⅲ)-NAu-2 reduction extent and initial As(Ⅲ) concentrations. Bioreduction of Fe(Ⅲ)-NAu-2 generated reactive Fe(Ⅲ)-O-Fe(Ⅱ) moieties at clay mineral edge sites. Anaerobic oxidation of As(Ⅲ) was attributed to the strong oxidation activity of the structural Fe(Ⅲ) within the Fe(Ⅲ)-O-Fe(Ⅱ) moieties. Our results provide a potential explanation for the presence of As(Ⅴ) in the anaerobic subsurface environment. Our findings also highlight that clay minerals can play an important role in controlling the redox state of arsenic in the natural environment.
基金financially supported by the Natural Science Foundation of China(Nos.41702040,41771272)Natural Science Foundation of Hunan Province(No.2021JJ40256)the Double First-Class Construction Project of Hunan Agricultural University(No.SYL2019043)
文摘It has been documented that organic contaminants can be degraded by hydroxyl radicals(•OH)produced by the activation of H2O2 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(5.2–16.9μmol/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 H2O2 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 H2O2-based treatments.
基金supported by National Natural Science Foundation of China(Grant No.40830849)National Key Basic Research Program of China(Grant No.2013CB429700)+1 种基金Shandong Province Natural Science Foundation of China for Distin-guished Young Scholars(Grant No.JQ200913)the Pilot Project of Knowledge Innovation Project,Chinese Academy of Sciences(Grant No.KZCX2-YW-211)
文摘The mineralogical and micromorphological characteristics of Si-Fe-Mn oxyhydroxides from the dacite-hosted PACMANUS hydrothermal field were analyzed.The samples are poorly crystallized Si-Fe-Mn oxyhydroxides with minor birnessite, todorokite, nontronite, goethite, and opal-A.There are some microtextures which are rather like fossil microbes such as the filamentous silica and the hollow pipes.Flakes of nontronite crystals are found either forming a honeycomb texture or distrib- uted on the surface of the hollow pipes.Nontronite is the product precipitated from low-temperature hydrothermal fluids, and microbes may play a role in its formation.Si-Fe-Mn oxyhydroxides have two kinds of nuclei: Si-Mn nuclei and Si nuclei, both enveloped by the similar Si-Fe outer layer, existing in the rod-shaped oxyhydroxide and spheroidal oxyhydroxide, respectively.In the Si-Mn nuclei, the concentration of SiO2 is between 39.32 wt% and 86.31 wt%, and MnO concentration is between 4.97 wt% and 27.01 wt%, but Fe2O3 concentration is very low (0.54 wt%-3.43 wt%).In the Si nucleus the concentration of SiO2 is 90.17 wt%, but concentration of MnO and Fe2O3 are low, with 0.06 wt% and 3.47 wt%, respectively.The formation of the Si-Mn nucleus is closely related to microbes, whereas the Si nucleus is of inorganic origin.
