Surface Hydroxyl Groups Of Silica Research Articles

Determination of the Orientation of Silanes on Silica Surfaces by Fourier Transform Infrared Photoacoustic Spectroscopy

Fourier transform infrared photoacoustic spectroscopy has been used for quantitative surface analysis of silica treated with trifunctional coupling agents such as γ-Methacryloxypropyltriethoxysilane (γ-MPS), γ-Glycidoxypropyltrimethoxysilane (γ-GPS), and γ-Aminopropyltri-ethoxysilane (γ-APS). The calibration curves are obtained for several characteristic bands of the coupling agents. Using a highly polarizable gas in the photoacoustic cell and comparing the spectra with a nonpolarizable coupling gas, it is possible to evaluate orientation of the coupling agents on the silica surface. The type of orientation is a function of the extent of surface coverage. At low surface coverage, coupling agents tend to take a perpendicular orientation with respect to the surface, and increasing surface coverage leads to parallel orientation. Increasing the coupling agent concentration also causes orientational changes of the species which form chemical bonds with the silica surface (hydroxyl, water, and carbonyl groups).

Separation of plasma membrane proteins of cultured human fibroblasts by affinity chromatography on bonded microparticulate silicas

Adsorbents for high-performance affinity chromatography were prepared by bonding proteins and reactive Procion triazine dyes to 3-isothiocyanatopropyl- and 3-aminopropylsilicas. The materials prepared were used successfully in the separation of hydrophobic plasma membrane proteins of cultured human fibroblasts. The data obtained show that the reaction of 3-isothiocyanatopropyltriethoxysilane (ITCPS) with the surface hydroxyl groups of silica yields a new and convenient route to preparing an “activated carrier” that is capable of coupling with potential affinity ligands containing amino functional groups. The reaction and bonding procedures of 3-isothiocyanatopropyltriethoxysilane and 3-aminopropyltriethoxysilane with silica were optimized with regard to a controlled and reproducible ligand density by adjusting the type of solvent and organic base as reaction catalyst. The ligand content of reactive triazine dyes directly coupled to 3-aminopropylsilica was significantly higher than that of the 6-aminohexyl derivatives coupled to 3-isothiocyanatopropylsilica. The stability of Procion Blue MX-R bonded to 3-aminopropylsilica and 3-isothiocyanatopropylsilica in phosphate-buffered aqueous solution at pH 5.0 and 8.0 was examined.

IR-TG同時測定によるシリカおよびアルミナゲル表面水酸基の熱的振舞

広い温度範囲で酸化物の加熱特性, 分子吸着, および表面反応などを測定することのできる赤外吸収スペクトルと熱重量分析のIR-TG同時測定装置を作製した。この装置を透明薄板状のシリカおよびアルミナゲルの常温から850℃の温度範囲における加熱特性の測定に用い, 表面水酸基の熱的振舞を研究した。 (1) シリカゲル表面水酸基のO-H伸縮振動帯の面積積分強度 (IA) と単位面積当たりのOH数 (NOH) とは比例し, 良好な直線関係となるが, シラノール濃度がおよそ2～3NoH以上の主として水素結合性OH (H-bondOH) の寄与する領域では, それ以下の自由OH (Free OH) の寄与する領域に比べ, 直線の勾配は増大する。この勾配の増加は, H-bond OHの振動子強度の増大によるとみられる。 (2) アルミナゲルのIAと重量減少率との関係は, 加熱昇温による固相状態の変化に依存し, 擬ベーマイト相では比例しないが, ηまたはδ相では比例する。 (3) η相のアルミナのIAとNOHとは, 比例し直線関係となるが, およそ3～4NOH以上の領域での直線の勾配は, それ以下の領域に比べわずかに増大する。この勾配の増大は, 3～4NOH以上の領域でのOH基の振動子強度の増加によるとみられ, 隣接OH基間の相互作用が比較的顕著な水酸基の存在に関係すると考えられる。

Hydrogen bonding in adsorption on silica

A spectral and calorimetric investigation was carried out into hydrogen bonding between the surface hydroxyl groups of silica and molecules of n-hexane, cyclohexane, carbon tetrachloride, benzene, nitromethane, acetonitrile, acetone, diethyl ether, dioxane, tetrahydrofuran, pyridine, and triethylamine. The integral intensity of the absorption band due to the stretching vibration of free hydroxyl groups on the surface of aerosil and the integral intensities of the absorption bands of these hydroxyl groups perturbed by adsorbed molecules were determined. From the difference in the heats of adsorption on hydroxylated and strongly dehydroxylated surfaces of a pure macroporous silica the heats of formation of the hydrogen bond between adsorbed molecules and free surface hydroxyl groups were evaluated. They were compared with the change in the integral intensity of the stretching vibration band of the hydroxyl groups resulting from adsorption and with their frequency shifts. The relation between the spectral and energetic characteristics of the hydrogen bond resulting from adsorption is approximately the same as that which occurs when the hydrogen bond is formed in solution.

Infrared study of the interactions of acetone and siliceous surfaces

Adsorbed acetone is held to silica surfaces by hydrogen bonds between surface silanols and the acetone carbonyl groups. Acetone is adsorbed by this mechanism on porous glass surfaces but there is also some decomposition, as shown by the increase in surface B—OH groups and by formation of new C—H absorptions at 2984 and 2940 cm−1. Experiments with boron-impregnated silica indicated that the presence of boron in the porous glass can account for this decomposition process. Bands at 1660–1670 and 1650 cm−1, observed when acetone and acetone-d6, respectively, were adsorbed on either porous glass or boron-impregnated silica, are attributed to ν(C=O) of the carbonyl group coordinated with a surface boron atom. The surface hydroxyls of both silica and porous glass could exchange with the deuterium of acetone-d6 via a mechanism involving an enol intermediate.

Infrared spectroscopy of solid surfaces and adsorbed molecules

The shift of the absorption band of silica surface hydroxyl groups on adsorption of molecules of different electronic structure is in accordance with their heat of adsorption and ionization potential. The change in the spectrum of benzene and its derivatives on adsorption by the hydroxylated silica surface and the cationized surface of zeolites is explained by the specific interaction of hydroxyl groups and cations of these surfaces with π-electrons of benzene ring and lone electron pairs of the O and N atoms of phenol and aniline. At low coverages, the spectrum of H 2O and CD 3OD molecules adsorbed on the cationized surface of zeolites is sensitive to the charge and radius of the cation. At higher coverages, the spectrum reflects both the interaction of these molecules with the cations of the zeolite and the mutual hydrogen bond. On the basis of the vibration theory, the spectra of H 2O and NH 3 molecules adsorbed on silica and zeolite have been analyzed.