Functionalization of polymeric membranes with phosphonic and thiol groups for water purification from heavy metal ions

Abstract

Membrane technologies are a useful solution for water treatment, especially for removing trace amounts of different pollutants. Current research is focused on improving the removal efficiency of polyvinylidene fluoride (PVDF) membranes to heavy metal ions, such as lead(II), cadmium(II), and chromium(III). The surface chemistry and morphology of PVDF membranes were varied applying the sol–gel approach for functionalization. It involved (1) diethylphosphatoethyltriethoxysilane (DPTES) or 3-mercaptopropyltrimethoxysilane (MPTMS) as functionalizing precursors, (2) different concentrations of the initial sols, and (3) NH4OH or HCl as the catalysts for the hydrolysis and co-condensation reactions. According to the SEM analysis of the surface texture, alkaline catalyst and low sol concentration result in the formation of porous membrane active layers. Membrane weight loss after water filtration under pressure indicated the dependence of layer stability on the conditions of functionalization, namely the membranes with phosphonic groups prepared in an acidic medium are more resistant to rinsing. Functionalized PVDF membranes demonstrated a significant increase in sorption efficiency along with high water flux. Overall, such membranes were sufficient for treating water with ion concentrations lower than 100 mg/L, whereas the applied functionalization technique is promising for adjusting the parameters of the final membranes.