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

• Published in: Separation and purification technology 2024-12, Vol.350, p.127957, Article 127957
• Main Authors: Kim, Minjae, Kim, Seonggon, Ahn, Hyungseop, Koh, Youngdeog, Kim, Kwangjoo, Lee, Min Kyung, Lee, Jae Won, Kang, Yong Tae
• Format: Article
• Language: English
• Subjects: Gas adsorption; H2O adsorption; HKUST-1; Hydrophobic coating; Metal Organic Frameworks (MOFs); Water stability
• ISSN: 1383-5866
• DOI: 10.1016/j.seppur.2024.127957

[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 H2O 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 CO2 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 CO2 adsorption capacity. In addition, when the N2 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.