Mesoporous organosilica membranes: Effects of pore geometry and calcination conditions on the membrane distillation performance for desalination

Abstract

Mesoporous organosilica membranes with different pore geometries and pore sizes (ranging from 2 to 12.9nm) were synthesized using an evaporation-induced self-assembly (EISA) method and different types of triblock copolymer (Pluronic F68 and F127). The surfactants were removed under different calcination conditions (temperature and air/inert environment) so as to modify the surface chemistry of the final material. The surface chemistry of the organosilica membranes heat treated under different atmospheres was slightly altered, and it was confirmed that calcination in air will inevitably lead to some cleavage of Si-C bonds in the 1, 2-bis(triethoxysilyl) ethane (BTESE) precursor. However, neither heat treatment fully decomposed either surfactant template, leaving some carbonaceous species on the pore wall. For the samples calcined in an inert atmosphere, this in turn increased the tortuosity of the pore channel and decreased membrane flux. Membranes templated with F68 demonstrated lower water fluxes (up to 13.5kgm -2 h -1) with excellent stability and salt rejection, whereas F127 templated membranes possessed larger pore sizes which yielded higher fluxes but the cage-like pores, combined with the hydrophilic surface, resulted in pore wetting.