Enhancing the dioxygen activation for arsenic removal by Cu0 nano-shell-decorated nZVI: Synergistic effects and mechanisms

Using copper and/or iron based nanomaterial to activate dioxygen to produce free radicals is an alternative and environmental friendly technique, but the low conversion efficiency of oxygen and the rate-limiting step of superoxide radical generation limit current application. In present work, Cu-0 nano-shell-decorated nZVI (CFNs) was synthesized and employed to enhance the activation of oxygen for the removal of arsenic at circumneutral pH. The adsorption and oxidation pathways of arsenic were investigated by determination of arsenic distribution and radical scavenger methods. The results showed that the removal of arsenic by CFNs involved the initial step of As ill adsorption by ferrihydrite followed by the oxidation of As-III by hydroxyl radical (center dot OHabs) and superoxide radical (center dot O-2abs(-)) radicals. In the presence of oxygen, the removal capacity of CFNs was improved twice than that of conventional nZVI (i.e. 453 mg/g and 263 mg/g, respectively). We inferred that Cu-I in-situ generated in heterogeneous catalysis was of increasing importance and the center dot O-2abs(-) produced from the activation of dioxygen was regarded as the key factor in the generation of H2O2 at pH 7. The enhancement of Cu-I generation mainly because of: (i) the facial loading of Cu-0 shell accelerated the generation of Cu-I, (ii) reductive Fe-0 core contributed to the regeneration of Cu-I, and (iii) the generation of ferrihydrite with high specific surface area favored the adsorption of oxygen. Hence, CFNs enhanced the electron transfer between Cu-I /Fe-II and O-2, increased the utilization efficiency of oxidants and improved the effectiveness of the functional nanoparticles for environmental applications.