The adsorption properties of various organo-modified mesoporous silicas towards a methoxy-modified chlorophenol in water have been studied. Phenyl, propyl, hexyl and hexadecyl groups were selected to study the possible interactions that the pollutant could preferentially develop with the surface sites. The best performing sample appears to be the hexyl-modified porous silica and one of the least performing the un-modified mesoporous silica. The physical state of the adsorbed chlorophenol in these two confined environments as well as the pollutant/surface interactions were characterized by a combination of solid-state NMR techniques. The 1H and 13C NMR responses show a high mobility of the molecules in both the modified and un-modified silica, suggesting the absence of strong interactions between the pollutant and the surface, despite the large difference in the chemical nature of the silica surface sites.