Selective surface adsorption versus imprinting in amorphous microporous silicas

Selective adsorption of organic molecules on inorganic solids is an attractive property of inorganic materials. It was attempted to control molecular adsorption on inorganic surfaces by the preparation of porous silicas through a sol-gel process developed for the generation of selective adsorption sites by molecular imprinting. The materials were prepared by co-polycondensation of tetraethyl orthosilicate with R-Si(OR)(3), with R as a removable template. In competitive adsorption experiments on such imprinted porous oxides with mixtures of (-)-borneol, (-)-camphor and (+)-fenchol, selective adsorption of individual components has been observed. Detailed control experiments, however, confirmed that the adsorption selectivity is independent of the comonomer used in the sol-gel process, but dependent on the method of preparation. Adsorption selectivities are found to be dependent on the specific pore surfaces created by different preparation procedures. No evidence was found for the presence of selective cavities due to imprint effects. (C) 1999 Elsevier Science B.V. All rights reserved.