Development of hydrogen-selective triphenylmethoxysilane-derived silica membranes with tailored pore size by chemical vapor deposition

• Triphenylmethoxysilane was designed as a novel precursor for silica membranes.
• The membranes exhibited high permeation performance, reproducibility and stability.
• High H2 permeance of 10−6 mol m−2 s−1 Pa−1 and H2/SF6 ideal selectivity over 12,000.
• Membrane pore size was tailored with structured precursors containing phenyl groups.
• The pore size of the prepared membrane was estimated to be around 0.50 nm.

Amorphous silica membranes were developed, based on an in silico molecular design, to exhibit excellent hydrogen-selective performance for separating hydrogen from mixtures containing larger organic molecules, such as methylcyclohexane and toluene. Triphenylmethoxysilane (TPMS) was synthesized and used as a novel precursor to prepare membranes by the counter-diffusion chemical vapor deposition method. Under the optimized bubbler temperature and counter-diffusion chemical vapor deposition reaction time, the fresh membranes showed high reproducibility and high hydrogen permeance in the order of 10−6 mol m−2 s−1 Pa−1 and high H2/SF6 ideal selectivity of over 12,000 at 573 K. Moreover, the TPMS-derived membrane exhibited good stability after hydrogen regeneration, even after placement in a dehumidifier cabinet at room temperature for 90 days. Single gas permeation performance and normalized Knudsen-based permeance evaluation showed that the TPMS-derived membrane (three phenyl groups on the precursor) had a pore size of 0.486 nm, and exhibited looser structures with larger pore size than those of a diphenyldimethoxysilane (DPDMS)-derived membrane (two phenyl groups on the precursor). These results suggest that the pore size of silica membranes can be tailored with various structured silica precursors containing phenyl groups.

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