Thermal treated amidoxime modified polymer of intrinsic microporosity (AOPIM-1) membranes for high permselectivity reverse osmosis desalination

Abstract

Despite the commercial success of polyamide reverse osmosis (RO) membranes for desalination, shortcomings of the material intrinsic properties hinder the further improvement of RO membrane permselectivity towards more energy-efficient desalination. Exploring new polymer materials is thus important to overcome the limitation of existing RO membrane materials. This work reports an investigation on an amidoxime modified polymer of intrinsic microporosity (AOPIM-1) as a membrane material for reverse osmosis desalination. AOPIM-1 is casted into a defect-free dense membrane, and followed by a thermal treatment to finetune its structural feature for enhanced salt rejection. As a polymer with stiff and distorted backbone structure, thermal treated AOPIM-1 possesses a high free volume and highly connected 0.3–0.8 nm micropores that provide fast water transport routes while regulating the permeation of ions. The rapid transport through the microporous channels gives the AOPIM-1 membrane a water permeability of 1.92 × 10−7 m·kg/m2·h·bar with NaCl rejection as high as 98.5 %. The thickness-normalized water permeability of AOPIM-1 membrane exhibits order-of-magnitude improvement comparing to conventional polyamide-based desalination membranes, and the permselectivity of the membrane is also found to be on the high side. This study confirms the possibility of utilizing microporous polymers as reverse osmosis membrane materials for high performance desalination.