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Al2O3 films were deposited with atomic layer control inside the pores of Anodisc alumina membranes. To achieve this controlled deposition on a high aspect ratio structure, a binary reaction for Al2O3 chemical vapor deposition (2Al(CH3)3 + 3H2O → Al2O3 + 6CH4) was separated into two half-reactions:  (A) AlOH* + Al(CH3)3 → Al-O-Al(CH3)2* + CH4 and (B) AlCH3* + H2O → AlOH* + CH4, where the asterisks designate the surface species. The trimethylaluminum [Al(CH3)3] (TMA) and H2O reactants were employed alternately in an ABAB... binary reaction sequence to deposit the Al2O3 film. Because each half-reaction is self-limiting, atomic layer controlled Al2O3 deposition was achieved on the surface of the high aspect ratio pores. To determine the necessary reaction conditions, surface species during each half-reaction were periodically monitored using in situ transmission FTIR spectroscopy. Ex situ gas flux and permporometry measurements were also performed to determine the effect of the binary reaction sequence on the pore diameter. Gas flux measurements for H2 and N2 were consistent with a progressive pore size reduction versus the number of AB reaction cycles. The permporometry measurements showed that the original pore diameter of ∼220 Å was reduced to ∼140 Å after 120 AB reaction cycles.

We report an experimental investigation of the adsorption properties of two important small-pore metal–organic framework (MOF) materials recently identified for gas separation applications, through the development and use of a high-pressure/high-temperature quartz crystal microbalance (QCM) device. In particular, we characterize in detail the CO2, CH4, and N2 adsorption characteristics of the MOFs Cu(4,4′-(hexafluoroisopropylidene)bisbenzoate)1.5 (referred to as Cu–hfipbb) and zeolitic imidazolate framework-90 (ZIF-90). We first describe the construction of a QCM-based adsorption measurement apparatus. Single-component adsorption isotherms of CO2, CH4, and N2 in the two MOFs were then measured at temperatures ranging from 30 to 70 °C and pressures ranging from 0.3 to 110 psi. In both materials, the order of adsorption strength is CO2 > CH4 > N2. We find that adsorption in the 1-D channels of Cu–hfipbb can be well described by a single-site Langmuir model. On the other hand, adsorption in ZIF-90 follows a more complex behavior, commensurate with its pore structure consisting of large porous cages connected in three dimensions by small windows. The nongravimetric QCM-based measurement techniques are shown to be a valuable microanalytical tool for the study of molecular adsorption in MOFs.

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An organic-inorganic hybrid membrane was developed by modification of a mesoporous Vycor glass with the organosilane heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane (HDFS). The presence of silane on the surface of Vycor glass was confirmed by Fourier transform infrared spectroscopy. A decrease in the surface area of the membrane after modification, measured by N 2 adsorption, suggested that the silane molecules effectively filled or blocked the pores. The permeance was governed by the kinetic diameter of gases with contributions from the surface flow for condensable gases. The membrane showed selectivity for CO 2 over other gases, whereas the untreated membrane was selective for n-C 4 H 10 . Mixed-gas selectivities were higher than pure-gas values for all gas pairs, which might be because of an enhanced permeance of CO 2 at low pressure usually observed for glassy polymers. In comparison to the HDFS membrane, the sorption of gases controlled the permeance of the octadecyltrichlorosilane (ODS) modified membrane, resulting in a significant change in the order of selectivity. The order of the permeance was CO 2 > Ar > CH 4 > n-C 4 H 10 > C 2 H 6 > N 2 > SF 6 >i-C 4 H 10 for the HDFS membrane, which changed to n-C 4 H 10 > i-C 4 H 10 > CO 2 > C 2 H 6 > He > N 2 for the ODS membrane.