A Facile and General Approach to Enhance Water Resistance of Metal-Organic Frameworks by the Post-Modification with Aminopropyltriethoxylsilane.

The water sensitivity of metal-organic frameworks (MOFs) as a common and crucial issue has greatly hindered their practical applications. Here, we present a facile and general approach to improve the water resistance of a typical MOF, i.e., CuBTC [Cu(BTC)(HO)] (BTC = benzene-1,3,5-tricarboxylate) using a post-modification reaction with aminopropyltriethoxylsilane (APTES) at room temperature. The afforded material is denoted as CuBTC@APTES. Various spectroscopic methods reveal that the organosilicon linkers have been successfully grafted onto CuBTC by electrostatic attraction between acid and base groups and without affecting the original coordination mode and basic structure. Compared with CuBTC, the water stability of CuBTC@APTES was significantly improved. The pristine CuBTC almost lost all its crystallinity, morphology and pore structure after 3-day treatment in water, while CuBTC@APTES is able to retain its main crystal structure and basic porosity after the same treatment. This finding can be explained by the successful introduction of the organosilicon molecular overlayer on the periphery of CuBTC to slow down the destruction of weak metal coordination bonds by water molecules, thus improving the water stability of CuBTC. The solution of water sensitivity provides more opportunities for the practical applications of CuBTC, such as aqueous phase catalysis and gas separation in humid environments. This simple approach can certainly be expanded to improve the water resistance of other carboxylate-containing ligand-based MOFs.