Influence of pH and ionic strength on the deposition of silver nanoparticles on microfiltration membranes

Abstract

In this study, we investigated the influence of pH and ionic strength on the deposition of silver nanoparticles (AgNPs) on cellulous acetate microfiltration membranes. Results indicated that flux and total silver concentration in the permeate increased with increasing pH. AgNPs and membrane zeta potential measurements suggest the increased flux and particle breakthrough with increasing pH were a result of more repulsive particle–particle and particle–membrane interactions. The greater repulsive interactions under these conditions resulted in less AgNP deposition, greater particle breakthrough, and higher water flux. Increasing ionic strength, on the other hand, increased deposition and reduced total silver in the permeate, at least at pH 4. This lower silver concentration observed in the permeate presumably was a result of the screening of repulsive electrostatic particle–particle and particle–membrane interactions and the resulting steric exclusion caused by membrane fouling. At higher pH values (7.6 and 10), however, no difference in flux decline was observed at different ionic strengths and significant breakthrough of silver occurred. These results at higher pH values suggest that sodium chloride facilitated the dissolution of AgNPs and the formation of AgCl, AgCl2− and AgCl32− on the particle surface, which enabled soluble silver complexes and AgNPs to penetrate the membrane.