Gas transport properties of polybenzoxazole–silica hybrid membranes prepared with different alkoxysilanes

The gas transport properties of polybenzoxazole (PBO)–silica hybrid membranes were investigated. The PBO–silica hybrid membranes were prepared with poly(o-hydroxy amide) (PHA) as a precursor and various alkoxysilanes via thermal oxazolization and sol–gel processes. The thermal decomposition temperature of the hybrid membranes increased with increasing silica content, indicating that the thermal stability was improved by hybridization with silica. The gas permeabilities of the PBO–silica hybrid membranes also increased with increasing silica content and thermal treatment temperature. It is worth noting that the hybrid membranes prepared with tetraethoxysilane (TEOS) as the selected alkoxysilane showed simultaneous enhancements in CO2 permeability and CO2/CH4 selectivity with increasing silica content and thermal treatment temperature. The prominent CO2/CH4 separation ability of the PBO–silica hybrid membranes prepared with TEOS might be attributable to free volume holes created around the polymer/silica interfacial area and increased intermolecular chain distance, which improved size-selective CO2/CH4 separation.