Investigation on sacrificial hydrolysis reaction of octadecyltrimethoxysilane for moisture resistance enhancement of metal–organic framework.

[Display omitted] • Hydrophobic surface treated HKUST-1 (HHK-x) is manufactured. • High stability in continuous exposure to moisture containing air condition. • Sacrificial hydrolysis reaction of hydrophobic layer protects the structure. • Water sorption resistance is enhanced by 50.2 % compared to pristine HKUST-1. Imparting water resistance is important for structures which is vulnerable to moisture to maintain the performance. In this study, octadecyltrimethoxysilane (ODTMS), which forms a hydrophobic surface through polymerization on the surface of the material, was used to enhance the hydrophobicity of HKUST-1 (HHK-x). This self-assembled structure reacts as sacrificial barrier to continuously penetrating H 2 O molecules and this effect is evaluated with detection of O–H peak (3323 cm−1) in FT-IR spectra. The gas adsorption performance is conducted with CO 2 gas and the adsorption amount was reduced by 20 % (from 5.77 to 4.62 mmol/g at 25 °C, 1 bar) compared with the pristine HKUST-1 following the trend of specific surface area. However, water adsorption amount was reduced by 50.2 %, which is 2.5 times higher than the decrease in CO 2 adsorption capacity. In addition, when the N 2 adsorption and cycle adsorption performances were compared after exposing the sample to air for five days, it was confirmed that HHK-40 maintained its microporous structure and stable performance. The manufactured materials exhibited higher durability in a cyclic vapor sorption test depending on the loading amount of ODTMS and exhibits different tendency depending on the rate of humidity. These results experimentally indicate that accessible self-assembly process of ODTMS on water-vulnerable materials to be sustainable and stable in humid air conditions. [ABSTRACT FROM AUTHOR]