Membrane synthesis via in-situ pore formation in silica gels through dynamic miscibility with soybean oil

The dynamic miscibility between soybean oil and organic silica precursors during sol-gel synthesis was used to tailor the microstructure of gels made with tetraethoxysilane (TEOS) or TEOS + methyltrimethoxysilane (MTMS). Soybean oil was investigated as an environmentally friendly and cheaper alternative to other common porogens. Oil concentrations of 9.09 v/v% and 33.33 v/v% were studied. For both TEOS and TEOS+MTMS gels, the miscibility of the oil and precursor decreased as the silica gel network formed, leading to oil-rich regions within the silica matrix. Solvent exchanges on gels or calcined on dried gels (i.e., xerogels) were performed to remove the oil from the silica, creating membranes with hierarchical pore structures. The pore structure of TEOSMTMS gels appeared finer and more interconnected compared to the isolated pores observed in gels made with only TEOS. Xerogel membranes made with TEOS+MTMS had higher specific surface areas (SSAs) than those made with TEOS. For oil concentrations of 33.33 v/v%, xerogels made from TEOS+MTMS had an average SSA of 1068 + 113 m2 g-1, an order of magnitude higher than the average SSA of 103 + 6 m2 g-1 for xerogels made with TEOS.