Development of Inorganic Silica Reverse Osmosis Membranes by Using a Counter-Diffusion Chemical Vapor Deposition Method

Abstract

Silica hybrid membranes have been developed for use as reverse osmosis (RO) membranes by using a counter-diffusion chemical vapor deposition (CVD) method. A silica source (phenyltrimethoxysilane; PhTMOS) and O3 were provided at opposite sides of a porous alumina substrate at 300°C for 90 min. The RO permeation test was conducted for 100 mg L−1 NaCl at 3.0 MPa. The highest NaCl rejection was 94.2% for a total flux of 1.7 kg m−2 h−1. The module length is an important factor in obtaining highly selective RO membranes. The short module (6 cm) was better because of the higher O3 concentration in the module. The decomposition conditions of phenyl groups on the silica surface are discussed for the hydrolysis powder of PhTMOS. According to FT-IR measurements, phenyl groups remained on the silica surface after O3 treatment for 90 min at 300°C, whereas the number of silanol groups decreased by approximately 30% upon O3 treatment at 300°C. The high Na+ rejection can be explained by the reduction of the silanol groups in the membrane.