Synthesis of mesoporous carbon-silica nanocomposite water-treatment membranes using a triconstituent co-assembly method

A direct synthesis method is introduced to prepare mesoporous carbon-silica nanocomposite (CSN) membranes for water-treatment applications. Unlike the intricate and expensive nanocasting method, this triconstituent co-assembly method is a one-pot synthesis method using Pluronic F127 as the templating agent with a hybrid organic-inorganic matrix formed by tetraethylorthosilicate (TEOS), resorcinol and formaldehyde. The silica content is varied in the polymer solution to investigate the material properties, stability of the nanocomposite mesostructure and membrane performance in vacuum membrane distillation (VMD). The CSN materials are carbonised under nitrogen at temperatures of 600-900 degrees C without any significant lattice shrinkage, demonstrating excellent stability. They possess a highly ordered porous structure with moderate BET surface area (430-550 m(2) g(-1)) and narrow pore size distribution at around 5.5-7.6 nm. Based on the FTIR and NMR analyses, there is no covalent bond between the carbon and silica networks, but the carbon compound was found to affect the condensation degree of the silica. Raising the temperature from 700 to 900 degrees C leads to further condensation of the carbon network, which in turn releases hydroxyl or water groups that can attack adjacent siloxane bonds. The CSN membranes performed well in VMD with water permeation flux up to 12 L m(-2) h(-1) and salt rejection >99%. This work shows that a different strategy of modifying silica-based membrane can be successfully applied for the desalination of saline waters through VMD.