Surface Treatment of Silica Gels with Acetone- or Hexane-Solution of Alcohols or Phenols with Some Functional Groups and the Chemical Nature of their Surface Groups

Abstract

The surface of silica gel was treated in an autoclave by the solution of alcohol or phenol with some functional groups in hexane or acetone, and their surface properties were investigated by determining their preferential dispersion into the media consisting of two immiscible components such as n-hexane and water. Furthermore, the identification of the surface groups and their thermal and chemical natures were examined through the infra-red spectra, differential thermal analysis (DTA), thermogravimetry (TGA) and qualitative analysis.The conclusions obtained are as follows: (1) The silica gels treated by diethylene glycol, 3-chloropropanol, phenol, or salicylic acid were hydrophilic whereas the ones treated by o-, m-, or p-cresol and hydroxybenzol were hydrophobic (lipophilic). (2) The characteristic absorptions due to alcoxy or phenoxy groups were observed in the infra-red spectra of the surface-treated silica gels. Since the intensity of the absorption at 950cm-1 due to bending vibration of Si-OH was almost the same for both the untreated and phenol-treated silica gels, it is still questionable whether silanol combines chemically with phenol or not. (3) DTA showed the exothermic due to dissociation and oxidation of the surface groups at 250°C, which is higher than the normal boiling point, and the remarkable exothermic due to oxidation of deposited carbon. Therefore, the surface groups are considered to combine with silanol chemically, except phenol. (4) These surface groups are confirmed to be alcoxy or phenoxy, since they were dissolved into boiling water or boiling dil. H2SO4 and, furthermore, from the qualitative analysis of dissolved solution, they were confirmed being alcohol or phenol used in this study.