Methyl-Shield Cu-BTC with High Water Stability through One-Step Synthesis and In Situ Functionalization

Abstract

Cu-BTC is a copper paddlewheel-based metal–organic framework (MOF) with great potential in gas adsorption and heterogeneous catalysis but has restricted practical applications because of its poor water stability. In this work, we propose a strategy for one-step synthesis and in situ functionalization of isopropanol (IPA)-modified Cu-BTC (Cu-BTC-IPA) with enhanced water stability. Successful incorporation of IPA into Cu-BTC was evidenced by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy spectra. The introduction of methyl groups around unsaturated Cu sites can form a methyl-shielding microenvironment, endowing Cu-BTC-IPA with the ability to maintain the topology structure after being immersed in water even for 4 days. After soaking, Cu-BTC-IPA can preserve 95% of its original Brunauer–Emmett–Teller (BET) surface areas and 90% of its initial CO2 adsorption capacity, while Cu-BTC completely lost its crystallinity. In addition, Cu-BTC-IPA managed to preserve its main crystal structure and 83% of its initial BET surface areas after 12 h of immersion in diluted HCl solution (pH = 3). The improved hydrolysis stability mechanism of Cu-BTC-IPA was investigated using density functional theory calculations. The results suggest that the strategy of incorporating IPA into Cu-BTC is very efficient in enhancing its structure stability against water and worthy of further exploitation in improving the structure stability of other MOFs with open metal sites.