Microporous organosilica membranes for gas separation prepared via PECVD using different O/Si ratio precursors

Abstract

Organosilica membranes for gas separation were prepared by plasma-enhanced chemical vapor deposition (PECVD) using three different types of silicon precursors: hexamethyldisiloxane (HMDSO), trimethylmethoxysilane (TMMOS), and methyltrimethoxysilane (MTMOS). Based on gas permeation measurement, the MTMOS-derived membrane showed the highest He/N 2 selectivity, followed by the TMMOS-derived and HMDSO-derived membranes. FT-IR characterization indicated that the HMDSO-derived membrane had the highest content of methyl group and the lowest Si-O-Si, while the methyl group content for the MTMOS-derived membrane was the lowest and Si-O-Si was the highest. These results suggest that the pore size of organosilica membranes could be tuned by changing the chemical structure of the silicon precursor. The MTMOS-derived membrane was further heat-treated to determine the effect of thermal annealing on gas-permeation properties. The gas permeances were drastically improved by the thermal annealing. After heat-treatment at 500C, the membrane showed a high H 2 permeance of 6.5  10 -7 mol/(m 2 s Pa) with a H 2 /SF 6 selectivity of 410 at 200C, and 5.6  10 -7 mol/(m 2 s Pa) with a H 2 /SF 6 selectivity of 360 at 50C.

Characterization of the deposition behavior and changes in bonding structures of hexamethyldisiloxane and decamethylcyclopentasiloxane atmospheric plasma‐deposited films*

“…The assumption that the density is the same for all of the coatings is not necessarily a good assumption. Previous studies have shown that the porosity and density change with deposition conditions . Characterization of the rate of deposition by mass per area would be preferred.…”

“…Gaussian fits are used, which is commonly used for solid samples due to the lack of motion and a statistical distribution of environments . Table shows the peak assignments based on published literature that were used to evaluate the bonding structures and functional groups present in the films.…”

“…Several reviews have been published on various types of atmospheric plasma processes . Numerous studies using various atmospheric plasma techniques have been reported for PECVD of organosilicon materials …”

“…As a relatively simple and inexpensive organosilicon, hexamethyldisiloxane (HMDSO) is a widely studied precursor for PECVD processes . However, HMDSO is highly flammable with a rating of 4 for flammability and has a German water rating of 3 (severe hazard to water).…”

Synthesis of Silica Membranes by Chemical Vapor Deposition Using a Dimethyldimethoxysilane Precursor

“…Silica-based membranes have been known to be effective for selective hydrogen permeation for more than 30 years, and are potentially less expensive than palladium-based membranes. The subject of silica membranes has been covered in recent reviews [1][2][3] and several recent papers [4][5][6][7][8]. Notable past work includes the original papers [9,10], the use of sol-gel techniques [11,12], chemical vapor deposition (CVD) [13,14] and plasma methods [15,16], the employment of diverse CVD precursors [17][18][19][20][21] and compositions [22][23][24], the determination of porosity [25], and the elucidation of the mechanism of permeation [26][27][28].…”