摘要
This research examines bonding methodology, surface coverage and silanol conversion efficiencies on the preparation of silica hydride (SiH) intermediate from triethoxysilane (TES) and dimethylmethoxysilane (DMMS) using sc-CO2 and dioxane as reaction solvent. Under sc-CO2 reaction conditions (at temperature and pressure of 100 掳C, 414 bar, respectively and 3 h reaction time), the surface coverages of SiH (evaluated from%C obtained from elemental analysis) prepared with DMMS (3.39 渭mol/m2) and TES (4.46 渭mol/m2) increased by 2- and 4-folds respectively, when compared to reaction performed in dioxane (2.66 渭mol/m2, SiH, DMMS and 0.69 渭mol/m2, SiH, TES). The relatively higher surface coverage of SiH from TES over DMMS generated in sc-CO2 is due to the inherent trialkoxy moiety of the TES that favours siloxane crosslinkage, forming polymeric surface attachments to yield a higher ligand density than the monomeric DMMS ligand. A conversion efficiency of 鈭?4.4%of SiH prepared from TES in sc-CO2 estimated from 29Si CP/MAS NMR analysis is comparable to TES silanization in dioxane or toluene. Moreover, silica hydride (SiH) conversion efficiency of ca. 42.4%achieved for the hydride intermediate prepared from DMMS in sc-CO2 is more superior to 33.3%efficiency obtained in dioxane. The differences in conversion efficiencies is attributed to the ability of sc-CO2 being able to access silica pores that are inaccessible in organic solvents. Bonded silica hydride from TES, DMMS prepared in sc-CO2 were characterized using elemental analysis, thermogravimetric analysis (TGA), BET surface area, Fourier transform infrared (FI-IR) and solid state NMR spectroscopy. Silica hydride technology/chemical functionalization of silica in sc-CO2 avoid extended purification steps (i.e. filtration and washing), generation of waste organic solvent and the need of costly or energy consuming drying processing with improved modification efficiency.