In Situ ATR-FT-IR Kinetic Studies of Molecular Transport and Surface Binding in Thin Sol-Gel Films: Reactions of Chlorosilane Reagents in Porous Silica Materials

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• 作者：Dion Rivera and Joel M. Harris
• 刊名：Analytical Chemistry
• 出版年：2001
• 出版时间：February 1, 2001
• 年：2001
• 卷：73
• 期：3
• 页码：411 - 423
• 全文大小：160K
• 年卷期：v.73,no.3(February 1, 2001)
• ISSN：1520-6882

文摘

ATR-FT-IR spectroscopy was employed to study the kinetics of transport and binding within thin silica sol-gelfilms. Studies of transport of several nonbinding probemolecules n-heptane, toluene, and 2-propanol, showedthat slow diffusion occurs within the micropores of thesol-gel films which could be modeled as a single-exponential accumulation in agreement with numericalmodels for diffusion in constricted pores. The rate oftransport into the film was found to decrease for molecules that interact strongly with the silica surface, whichis consistent with adsorption inhibiting the transport ofmolecules through the pores. In situ spectroscopic studies of surface reactions with diphenylchlorosilane (DPSiCl) reveal that DPSiCl reacts quickly with surface waterto form diphenylhydroxysilane (DPSiOH), the reactivespecies detected within the film. Analysis of the time-dependent infrared spectra reveals both transport andsurface-binding steps in the reaction kinetics. From themagnitudes of the rate constants and the correspondingpure component spectra, it is determined that the surface-binding component is responsible for accumulation ofmost of the silane at the silica surface. Ex situ spectroscopic studies confirm that Si-O-Si bond formationoccurs at room temperature in these sol-gel films. Studies of chlorosilane reactions at silica surfaces pretreatedwith triethylamine were conducted to investigate theinfluence of amines on this chemistry; it was determinedthat the amine enhances the transport of more reagentmolecules to the silica surface while the intrinsic rate ofthe binding reaction is not significantly changed.