This paper discusses the toxicity and mobility of chromium species. And it presents the extent and kinetics of reductive remediation of hexavalent chromium, Cr+ using ferrous ion, Fe2+. Molar ratios of 1:3 and 1:6 of ...This paper discusses the toxicity and mobility of chromium species. And it presents the extent and kinetics of reductive remediation of hexavalent chromium, Cr+ using ferrous ion, Fe2+. Molar ratios of 1:3 and 1:6 of Cr (VI) to Fe (II) were used. Integral method of data analysis showed reaction followed second-order kinetics with R square values near unity. Reaction was initially fast but with a rapid precipitation attributed to Cr (III)-Fe (III) in previous studies. This colloidal precipitate ultimately stops the reaction, which explains while conversion efficiency increases with increased molar ratio of Cr (VI) to Fe (II). The impact of pH was investigated by adjusting the Cr (VI)-Fe (II) medium to pH 2.78, 5.24, 7.00, 9.00 and 11.96 using predetermined drops of acid or base. Reaction was more rapid under alkaline conditions with higher extent of degradation consistent with previous research. In soil system, mass transfer limitation was hardly noticed as high extent of reduction was recorded relative to aqueous phase. The high solubility of Cr (VI) aided the release into the aqueous media for reduction by ferrous sulfate.展开更多
Cost-effective 3d transition metal(TM) based single atom catalysts(SACs) for oxygen reduction reaction(ORR) are potential alternatives for Pt-based electrocatalysts in fuel cells and metal-air batteries.Understanding ...Cost-effective 3d transition metal(TM) based single atom catalysts(SACs) for oxygen reduction reaction(ORR) are potential alternatives for Pt-based electrocatalysts in fuel cells and metal-air batteries.Understanding the effects of SACs’ properties and active site composition on the catalytic performance is significant to construct highly efficient catalysts. Here, we successfully promote the activity of cobalt single atoms decorated on N-doped carbon nanosheets via tuning the content of different nitrogen components, which outperforms most reported cobalt SACs. The activity and kinetics show positive correlation trends with the content of Co-Nxand graphitic N, serving as the main active sites.Furthermore, ORR kinetics in alkaline media can be positively affected by the conductivity of catalysts while no similar relation is observed in acidic media. The slight loss of Co-Nxsites engenders a mild change of performance in alkaline media, while the decrease of Co-Nxsite activity due to chemical oxidation of carbon support and the loss of Co-Nxsites in acidic media exacerbate the degradation of performance. Our work provides an insight into the relation between ORR electron transfer kinetics and active sites in 3d TM based SACs.展开更多
文摘This paper discusses the toxicity and mobility of chromium species. And it presents the extent and kinetics of reductive remediation of hexavalent chromium, Cr+ using ferrous ion, Fe2+. Molar ratios of 1:3 and 1:6 of Cr (VI) to Fe (II) were used. Integral method of data analysis showed reaction followed second-order kinetics with R square values near unity. Reaction was initially fast but with a rapid precipitation attributed to Cr (III)-Fe (III) in previous studies. This colloidal precipitate ultimately stops the reaction, which explains while conversion efficiency increases with increased molar ratio of Cr (VI) to Fe (II). The impact of pH was investigated by adjusting the Cr (VI)-Fe (II) medium to pH 2.78, 5.24, 7.00, 9.00 and 11.96 using predetermined drops of acid or base. Reaction was more rapid under alkaline conditions with higher extent of degradation consistent with previous research. In soil system, mass transfer limitation was hardly noticed as high extent of reduction was recorded relative to aqueous phase. The high solubility of Cr (VI) aided the release into the aqueous media for reduction by ferrous sulfate.
基金financial support from the Natural Science Foundation of Beijing Municipality (2191001)the National Natural Science Foundation of China (51631001, 51672010 and 52001007)+1 种基金the National Key R&D Program of China(2017YFA0206301)the China Postdoctoral Science Foundation (2020M670038)。
文摘Cost-effective 3d transition metal(TM) based single atom catalysts(SACs) for oxygen reduction reaction(ORR) are potential alternatives for Pt-based electrocatalysts in fuel cells and metal-air batteries.Understanding the effects of SACs’ properties and active site composition on the catalytic performance is significant to construct highly efficient catalysts. Here, we successfully promote the activity of cobalt single atoms decorated on N-doped carbon nanosheets via tuning the content of different nitrogen components, which outperforms most reported cobalt SACs. The activity and kinetics show positive correlation trends with the content of Co-Nxand graphitic N, serving as the main active sites.Furthermore, ORR kinetics in alkaline media can be positively affected by the conductivity of catalysts while no similar relation is observed in acidic media. The slight loss of Co-Nxsites engenders a mild change of performance in alkaline media, while the decrease of Co-Nxsite activity due to chemical oxidation of carbon support and the loss of Co-Nxsites in acidic media exacerbate the degradation of performance. Our work provides an insight into the relation between ORR electron transfer kinetics and active sites in 3d TM based SACs.
