Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions.

The silanol group and its role in liquid chromatography

Adsorption of organic molecules on silica surface.

The gas-phase reaction of (3-aminopropyl)dimethylethoxysilane (APDMES) with silica with and without amine catalysts has been studied using infrared spectroscopy. Evidence is provided that shows that the aminosilane initially adsorbs via hydrogen bonding of both ethoxy and aminopropyl moieties of the silane with the surface hydroxyl groups. As the reaction proceeds, the number of silane molecules attached to the surface via a Si-O-Si linkage increases primarily at the expense of the number of H-bonded ethoxy groups. The conversion is due to a catalytic process involving the aminopropyl end of gaseous APDMES molecules. On the other hand, the H-bonded aminopropyl groups are less reactive and only a small portion of these groups participates in Si-O-Si bond formation. At the end of the reaction there remain about 50% of the adsorbed APDMES attached by the H-bonded aminopropyl group. Attempts to block the adsorption of the aminopropyl end through the use of the more strongly H-bonded triethylamine proved unsuccessful. The use of preadsorbed triethylamine or 1 : 10 mixtures of triethylamine/APDMES accelerates the reaction but in the end leads to the same final distribution of products on the surface. Copyright 2000 Academic Press.

Reaction of (3-Aminopropyl)dimethylethoxysilane with Amine Catalysts on Silica Surfaces

High-resolution solid-state NMR techniques were used to investigate the surface structure of Cab-O-Sil fumed silica. 1H NMR results obtained from CRAMPS, MAS-only and relaxation studies reveal the existence of both hydrogen-bonded silanols and isolated silanols on the Cab-O-Sil surface. A systematic dehydration study of fumed silica was carried out, with results on the quantity of each type of silanol on the surface at various dehydration stages. 29Si CP-MAS experiments, including CP spin dynamics studies and various other relaxation studies, were employed to probe hydrogen bonding and the local structural environments of various hydroxyl groups of silica surfaces. 29Si CP-MAS experiments on water-treated and deuterium-exchanged Cab-O-Sil indicate the existence of interparticle silanols and internal silanols in fumed silica. 1H and 29Si NMR show that for fumed silica both isolated and hydrogen-bonded silanols are present on the surface of an untreated sample, in contrast to the case of silica gel, where a...

The Fumed Silica Surface: A Study by NMR

Infrared spectroscopy has been used to study the vibrational modes associated with free (isolated) silanol groups on an aerosil silica and a precipitated silica which have been activated in vacuum in the temperature range from 450 to 800 o C. Both silicas exhibit two Si-O-H angle deformation modes at 760 and 840 cm -1 , indicative of two types of isolated silanol species, called type I and II, respectively

A. J. McFarlan

Papers

Surface vibrational modes of silanol groups on silica