Gas Adsorption Characteristics of Metal–Organic Frameworks via Quartz Crystal Microbalance Techniques

• Published in: Journal of physical chemistry. C 2012-07, Vol.116 (29), p.15313-15321
• Main Authors: Venkatasubramanian, Anandram, Navaei, Milad, Bagnall, Kevin R, McCarley, Ken C, Nair, Sankar, Hesketh, Peter J
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Solid surfaces and solid-solid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp304631m

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.