Thin-Film Approach to Rapid, Quantitative Measurements of Mixed-Gas Adsorption Equilibrium in Nanoporous Materials

Nanoporous adsorbent materials are a key part of many industrial processes, including the rapidly expanding carbon capture industry. The development of advanced sorbents requires an assessment of the sorbent’s performance under mixed-gas conditions. Existing measurement techniques tend to be slow, material-intensive, and have limited ability to measure competitive mixed-gas sorption. We have developed a novel technique that measures thin films of sorbents deposited onto sensitive microelectromechanical system (MEMS) transducers. This technique is fast, requires very little material, and enables real-time monitoring of binary gas sorption. We report measurements of CO₂/H₂O mixed-gas isotherms at three different temperatures on the carbon capture MOF CALF-20. The measured experimental data on CO₂/H₂O mixture adsorption in CALF-20 demonstrate the severe limitations of the Ideal Adsorbed Solution Theory (IAST) in providing a quantitative estimation of the component loadings. Departures from the IAST are quantified by the introduction of activity coefficients and the use of the Real Adsorbed Solution Theory (RAST).