Effect of sodium and potassium on polysaccharide fouling on PVDF and graphene oxide modified PVDF membrane surfaces

Abstract

This study presented the contribution of monovalent cations (Na+ and K+) to the adsorptive sodium alginate (SA) fouling in real-time using a quartz crystal microbalance and dissipation (QCM-D). Polyvinylidene fluoride (PVDF) and graphene oxide modified PVDF membrane (GO-PVDF) were selected as representative membrane materials. Atomic force microscopic (AFM) equipped with probes modified with foulant was used for exploring the adhesion force changes between SA and the membrane. The results showed that both Na+ and K+ can promote the adsorption capacity of SA on the membrane surface. SA fouling in Na+ condition was more severe than that in K+ circumstance due to higher attraction forces under identical ion strength. In addition, the GO-PVDF membrane is more readily/severely fouled than PVDF by SA when Na+ or K+ is present. The difference in the interaction forces was further interpreted using XDLVO theory. The results suggested that the Lewis acid-base adhesion free energy (ΔGflfAB) between SA decreased gradually with increasing Na+ concentration, while in the K+ environment, ΔGflfAB increased instead. Moreover, the increase of the Lifshitz-van der Waals components (γmLW) of the GO membrane, resulted in a higher attractive interaction in the initial phase of the SA fouling. The results of this study provide a microscopic analysis of the possible fouling mechanism of Na+ and K+ on membrane fouling and as well as provide insightful reflections for an appropriate approach (whether GO modified or not) to membrane fouling control.