pH-Dependent Transformation of Ag Nanoparticles in Anaerobic Processes

摘要

Silver nanoparticles (Ag-NPs) with increasing concentration have often been found in industrial and municipal wastewaters, which may potentially pose a new challenge on the human health and ecology. It has been reported that transformation of Ag-NPs to Ag_2S led to more than 71% reduction in their toxicity. Under oxic conditions, Ag-NPs can be transformed to Ag_2S via: 4Ag + O_2 + 2H_2S → 2Ag_2S + 2H_2O and 4Ag + O_2 + 2HS~ -→ 2Ag_2S + 2OH~-. However, the transformation mechanism of Ag-NPs in anaerobic processes where oxygen is not available has not yet been well understood. This viewpoint shows that the transformation of Ag-NP to Ag_2S in anaerobic processes is possible, but pH-dependent. Moreover, the pH-dependent transformation mechanism of Ag-NPs can likely be extended to other types of metal NPs present in anaerobic process. Therefore, in future evaluation of release and toxicity of metal NPs present in anaerobic processes, the pH effect on their transformations should be carefully taken into account.