One remarking case to introduce hydrophobic moieties in the silica membrane material was reported by De Vos et al. [16]. Methyltriethoxysilane (MTES) was embedded into a sol–gel process prepared with tetraethylor- thosilicate (TEOS), water, ethanol and nitric acid. This process introduces methyl groups to the silica matrix as template agents to enhance hydrophobicity.