Hydrophobisation of active carbon surface and effect on the adsorption of water

A technique of surface hydrophobisation has been applied to two microporous carbonaceous adsorbents. A granular active carbon and an activated carbon fibre, both formerly chemically treated in order they preferentially present hydroxyl surface functions, were modified by action of vinyltrimethoxysilane (vtmos) in liquid phase. The resulting samples were characterised using sorption of nitrogen, FTIR, XPS and Si-29 MAS-NMR spectroscopy, and elemental analysis. Their stability and heat treatment have also been investigated through thermal analysis. The efficiency of the hydrophobisation treatment was evaluated by static adsorption of water vapour and vapours of chlorinated volatile organic compounds (VOCs): dichloromethane and trichloroethylene. Grafting of the vtmos and development of a "coating" of polysiloxane onto the adsorbent induced a modification of the carbon surface but also a partial filling of the porosity. These modifications accounted for a decrease of both the amounts of water and VOC adsorbed by the hydrophobised materials. However, water uptakes were found to be much lower than those of the VOCs, evidencing an enhanced selectivity of the hydrophobised adsorbents toward VOCs. (C) 2005 Elsevier Ltd. All rights reserved.