title: Preparation and characterization of bonded silica hydride intermediate from triethoxysilane and dimethylmethoxysilane using supercritical carbon dioxide and dioxane as reaction medium.
abstract: 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-CO(2) and dioxane as reaction solvent. Under sc-CO(2) reaction conditions (at temperature and pressure of 100 °C, 414 bar, respectively and 3h reaction time), the surface coverages of SiH (evaluated from %C obtained from elemental analysis) prepared with DMMS (3.39 μmol/m(2)) and TES (4.46 μmol/m(2)) increased by 2- and 4-folds respectively, when compared to reaction performed in dioxane (2.66 μmol/m(2), SiH, DMMS and 0.69 μmol/m(2), SiH, TES). The relatively higher surface coverage of SiH from TES over DMMS generated in sc-CO(2) 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 ∼84.4% of SiH prepared from TES in sc-CO(2) estimated from (29)Si 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-CO(2) is more superior to 33.3% efficiency obtained in dioxane. The differences in conversion efficiencies is attributed to the ability of sc-CO(2) being able to access silica pores that are inaccessible in organic solvents. Bonded silica hydride from TES, DMMS prepared in sc-CO(2) 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-CO(2) 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.
authors.affiliation: Innovative Chromatography Group, Irish Separation Science Cluster, Department of Chemistry, and Analytical and Biological Chemistry Research Facility, University College Cork, Ireland. b.ashuashuarrah@ucc.ie
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Ashu-Arrah
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Glennon
authors.forename: Klaus
authors.initials: K
authors.lastname: Albert
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D004146:Dioxanes / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D016062:Porosity; D012821:Silanes / Q000737:chemistry*; D017640:Silicates / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013818:Thermogravimetry
chemical_list: D004146:Dioxanes; D012821:Silanes; D017640:Silicates; C487012:silica hydride; D002245:Carbon Dioxide; C522569:triethoxysilane