Characterisation of sol–gel silica films doped with chromium (III) acetylacetonate

Sol–gel silica films doped with chromium (III) acetylacetonate were synthesised on aluminium substrate and characterised by IR and UV–vis reflectance spectroscopy to study localisation and thermal transformations of doping Cr(acac)3 molecules. The involvement of CO groups of Cr(acac)3 molecules into hydrogen bonding with silanol groups of silica film was found out. Removal of doping Cr(acac)3 molecules located at the surface of the film was detected upon thermal treatment at 473 K because of their weak interaction with silica network. The process of elimination of acetylacetonate ligands from Cr(acac)3 molecules located inside the film and H-bonded to silica network was accompanied by Cr (III) to Cr (VI) oxidation which completed at 613 K with the predominant formation of dichromate-like species.