Preparation of loose nanofiltration PVDF membrane coated with dopamine and EPPTMS layers based on mussel inspired technique and ring-opening reaction via a facile VIPS-NIGPS method for dye separation applications

Abstract

In this work, vapor-induced phase separation (VIPS) coupled with non-solvent induced gelation phase separation (NIGPS), in which water was used as an additive to tailor loose nanofiltration (NF) membrane, was utilized to obtain an optimized and smoother primer PVDF membrane for efficient dye separation. Next, a polydopamine (PDA) layer was formed through the Mussel-inspired technique on the surface of the as-prepared PVDF membrane. Subsequently, an epoxy-propoxypropyl-trimethoxysilane (EPPTMS) layer was also fabricated on the PDA layer in order to enhance hydrophilicity and rejection performance of the prepared membrane. It was demonstrated that through the addition of external H2O (4%), viscosity was escalated due to the pre-gelation. Moreover, the NIGPS-VIPS process resulted in better consolidation of PVDF chains during de-mixing process, and therefore, led to the improved porosity and surface pore size. After the formation of PDA and EPPTMS layers, extraordinary separation and flux performance were obtained. The permeation rate across the membrane was as high as 15.5 L.m−2.h−1.bar−1, and the rejections of Crystal violet (CV), Methylene blue (MB), Methyl green (MG), Reactive red 120 (RR), and Direct yellow (DY) dye solutions (0.2 g/L) by the prepared PVDF/PDA/EPPTMS membrane were 99.1%, 98.1%, 98.6%, 90.3%, and 97.3%, respectively. Moreover, flux recovery rate was also enhanced from 59.0% to 94.2%, which was about 60% enhancement. The optimum membrane also exhibited an outstanding long-term rejection and long-term flux. All the separation tests demonstrated the extraordinary performance of the optimum membrane for dye rejection applications.