An economical and simple method for preparing highly permeable and chlorine-resistant reverse osmosis membranes with potential commercial applications

Abstract

The improvement in the overall efficiency of thin-film composite (TFC) reverse osmosis (RO) membranes is limited by their low permeability and sensitivity to degradation by chlorine. In the present study, polypiperazine (PIP), the commonly used amine monomer in preparing commercial TFC nanofiltration (NF) membranes, was used to regulate the m-phenylenediamine (MPD) based interfacial polymerization (IP) process. The results showed that addition of PIP optimized the micro-structure and surface properties of the polyamide (PA) layer. When the MPD and PIP mass ratio was 1 : 1, the TFC_W-1:1 membrane exhibited 70% flux enhancement compared to pure MPD-based TFC_W-1:0 membranes. Besides, the TFC_W-1:1 membrane exhibited better chlorine-resistant performance since the NaCl rejection declined to just 3.8% while it was 11.3% for TFC_W-1:0 membranes after immersion in 500 ppm NaClO solution for 48 h. Such improvement can be attributed to the increased number of unreacted amine groups and the thickness of the PA layer that PIP brought, which provided a sacrificial protective layer to consume the active chlorine, and thus maintain the integrity of the inner rejection layer. In all, the novelty and purpose of the present work is to find a more simple and scalable method to fabricate high-performance TFC RO membranes by using commonly, cheaply and frequently used materials.