Role of interfacial electron transfer reactions on sulfamethoxazole degradation by reduced nontronite activating H_(2)O_(2)

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.

Anaerobic oxidation of arsenite by bioreduced nontronite

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.