FT-IR spectra of benzidine (bnz), 2,2 ' -bipyridyl (2,2 ' -bpy) and 4-4 ' -bipyridyl (4-4 ' -bpy) adsorbed on natural diatomite from Kutahya-Alayunt (Anatolia, Turkey) have been investigated. Vibrational results indicate the presence of chemisorbed species. No physical sorbed species has been detected. Bnz and 2,2 ' -bpy treated diatomite samples were found to be coloured, whereas 4,4 ' -bpy treated diatomite was not altered in colour. The formation of cationic (bnz(+) and bnz(2+)) or anionic (2,2 ' -bpy(-)) surface species has also been detected in the case of bnz or 2,2 ' -bpy treated diatomite, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.