Template Synthesis Of Ordered Mesoporous Silica Membranes And Characterization Of Membrane Performance

In this paper, ordered mesoporous silica films were synthesized by surfactant templeted method using tetraethoxysilane (TEOS) and cteyltrimethylammonium chloride (CTAC) as the silicon-containing precursor and the templating agent, respectively, and supported mesoporous silica membranes were prepared by spin coating the silica sols on alumina support. Firstly,the effects of H2O/TEOS and HCl/ TEOS molar ratios on the hydrolysis rate of TEOS and the gelation rate were investigated. It was revealed from XRD patterns that a low gelation rate is favorable for the formation of highly ordered mesostructures of resultant films. The first and second critical micelle concentration (CMC1 and CMC2) of CTAC in the component solvent with EtOH/H2O molar ratio at 1:1 was characterized by Steady-state Fluorescence Method at 25℃. Comparing with the CMC1 and CMC2 of CTAC in water,it was showed that ethanol allows more CTAC to be added into the system and keep steady micelle state at the same time. The effects of CTAC/TEOS molar ratio on the pore size distribution and the order of the silica films were especially investigated. The films synthesized at molar ratios of 0.05,0.15,0.25 and 0.35 all showed a single narrow peak between 2 nm and 3 nm in pore size distribution, but those from 0.15 molar ratio of CTAC/TEOS had the highest ordered mesostructure. In addition, probable states of CTAC with the increase of CTAC/TEOS molar ratio were also discussed. TGA analysis reveals that CTAC can be removed completely and XRD patterns indicate that long time heat-treating at 600℃ has disadvantage on the ordered mesostructure. The instances of silica sols filtering into the alumina support were characterized by scanning electron microscopy (SEM). The supported silica membranes with CTAC/TEOS molar ratio of 0.35 shows the greatest permeation, and the permeation tests of N2 and H2 indicate that the Knudsen mechanism dominates the permeation of gases after six times coating process. The experimental separation factor for CH4/CO2 agrees with the ideal separation factor calculated from Knudsen mechanism.