Preparation of hydroxyl group containing bridged organosilica membranes for water desalination

Abstract Organosilica membranes were prepared by homo- and copolymerization of hydroxymethyl(triethoxy)silane (HMTES) for the first time, and applied to reverse osmosis (RO) to investigate the effects of the hydroxymethyl group. Fourier transform infrared (FT-IR) spectrometry, thermogravimetric analysis (TGA), and water contact angle measurements of the membrane surface indicated that the C–OH group of HMTES underwent a condensation reaction with Si–OH to form an Si–O–C bond during the calcination at 300 °C. Upon RO experiments using an NaCl aqueous solution, the HMTES membrane exhibited a significant increase of the liquid permeance and a decrease of the NaCl rejection during the measurement, which arose from the hydrolytic cleavage of the Si–O–C bond to form Si–OH and C–OH groups upon contact with water. On the other hand, for a membrane derived from the copolymerization of HMTES and bis(triethoxysilyl)ethane (BTESE) in the weight ratio of 1:1, liquid permeance was increased gradually to reach a steady state of 3.4 × 10 −13  m 3 /(m 2  s Pa), and NaCl rejection was maintained at a value as high as 95.5%. Thermal stability and chlorine resistance of the membranes were also studied.