Cost-effective Surface Modifications of Silica and Alumina Achieved by Way of a Simple In-house Set-up

Introduction Material surfaces composed of glass, metal oxide or potentially any oxide/hydroxide functional group are routinely tailored using organosilane reagents, affording new physico-chemical surface properties and enabling diverse application. The classic modification is based upon a hydrolysiscondensation mechanism. Reagent of the type YSiX3 (Y= terminally functionalized alkyl; X= alkoxide or chloride) is deposited out of protic solution and cured onto a surface to afford a coating with an approximate thickness of ten monolayers. In a second approach, which affords a thinner coating, organosilanes are made to react directly with surface functional groups. Covalent bonding has been rationalized via an assisted SN2-type displacement of alkoxide or chloride groups as opposed to the above sol-gel-like process. Clearly, the latter mode of reaction predominates in aprotic environments and only if the substrate contains no adsorbed proton source. Accordingly, reactions are routinely carried out in alcohol/water medium if hydrolysisdeposition is desired, and in dry toluene solution or in the gas phase at various pressures if displacement is preferred. In exploring cost-effective and environmentally green methods of achieving surface modification, a hybrid approach was developed in which organosilane vapor was deposited onto a surface at reduced pressures and activated in a second step by vapor-phase deposition of moisture or moisture/acetic acid. The method was found to be general in scope and amenable to mesoporous materials and to scale-up. The results presented herein describe the findings of a preliminary investigation conducted on silica gel & alumina chromatographic media.