Effect of Ge-doped silica membrane preparation conditions on the sol particle size and hydrogen permeation and separation performance

Ge-doped silica membranes were prepared by the co-hydrolysis and condensation of tetraethyl orthosilicate(TEOS) and ethoxy-germanium Ge(OC2H5)4 under different conditions.The effect ofsynthesis conditions on the particle size of Ge-doped silica sol and the hydrogen permeation and separation performance of the silica membranes derived from sol with different particle size were investigated in detail by dynamic light scattering and gas permeation measurement respectively.The results show the sol particle size increases with increasing in the amount of Ge(OC2H5)4 doped and the temperatures.Increasing in the acidic concentration leads to a decrease of sol particle size when the molar ratio of HNO3/TEOS is lower than 0.085,however,further increasing the molar ratio of HNO3/EtOH results in an increase in sol particle size.The sol particle size deceases with increasing in molar ratio of H2O/EtOH.Both permeance of H2 and CO2 increases with increasing in sol particle size,from 4.4×10-7 mol/(m2·s·Pa) at a particle size of 2.3 nm to 8.2×10-7mol/(m2·s·Pa) at a particle size of 90 nm for hydrogen.However,only membranes derived from sol with a size less than 4.5 nm exhibit a H2/CO2 permselectivity higher than that of Knuden diffusion.