Chemistry, Physics and Astronomy, Ames Laboratory
Journal or Book Title
Microporous and Mesoporous Materials
The post-synthesis functionalization (grafting) kinetics of mesoporous silica nanoparticles (MSN) with organo-trimethoxysilanes (R-TMS) is studied via solution 1H NMR spectroscopy. The process involves a rapid adsorption/desorption pre-equilibrium followed by reaction of R-TMS with surface silanols. Grafting rates are affected by the functional group in R-TMS. For example, the grafting rate of aminopropyl-trimethoxysilane (AP-TMS) is one order of magnitude higher than other R-TMS. High concentrations of AP-TMS result in substrate-inhibition kinetics, likely due to steric and mobility constraints for reactant alignment at high coverage. The higher rates of AP-TMS grafting indicate a catalytic effect of amine groups. This effect depends on the amine's basicity and can be used to control the grafting rates and degree of condensation of other R-TMS. Adjusting the rate of mercaptopropyl-trimethoxysilane (MP-TMS) grafting using amines gives MP-MSN materials of varying adsorptive and catalytic activities, illustrated by Pd scavenging experiments and use of Pd@MP-MSN as catalysts for a Suzuki-Miyaura cross-coupling reaction.
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Manzano, J. Sebastián; Wang, Hsin; Kobayashi, Takeshi; Naik, Pranjali; Lai, King C.; Evans, James W.; and Slowing, Igor I., "Kinetics of the functionalization of mesoporous silica nanoparticles: Implications on surface group distributions, adsorption and catalysis" (2020). Chemistry Publications. 1234.
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