Zeolites with various levels of micro- and mesoporosity are prepared by alkaline treatment of ZSM-5 at different temperatures. Terminal silanol groups generated at the mesopore surface during desilication are reacted with aminopropyltriethoxysilane or mercaptopropyltrimethoxysilane leading to the obtainment of hierarchical zeolites with organic-functionalized hybrid mesopores. Grafting of 3-aminopropyl and 3-thiopropyl moieties is directly evidenced by elemental analysis, nitrogen adsorption, thermogravimetry, and infrared spectroscopy, and the relative extents of surface functionalization of the purely microporous and of the mesoporous ZSM-5 zeolites are compared. Based on these results the mechanism of organosilane attachment is thought to be equivalent in both cases. Organic-functionalized mesopores exhibit good hydrothermal stability. The adsorption properties of the ZSM-5 samples both prior and post silanization are assessed for the uptake of lipase enzyme. Mesoporous zeolites show increased uptakes than the parent zeolite in all cases. This demonstrates that the mesoporosity enhances the adsorption of large guest species that cannot be accommodated within the micropores of their conventional counterparts. Immobilization on surface functionalized zeolites greatly improves the retention of lipase activity when applied in the hydrolysis of p-nitrophenylbutyrate.
Preparation of organic-functionalized mesoporous ZSM-5 zeolites by consecutive desilication and silanization
Mater. Chem. Phys. 2011, 127, 278-284.