THE INFLUENCE OF THE PHASE COMPOSITION OF MIXED-PHASE MESOPOROUS TiO2 ON ITS PHOTOCATALYTIC ACTIVITY IN THE REACTION OF HYDROGEN EVOLUTION FROM AN AQUEOUS-ETHANOL MIXTURE

Abstract

Two- and three-phase compositions of mesoporous nanocrystalline TiO2 (meso-nc-TiO2) were obtained from sol-gel reaction mixtures (ZGRM) using dibenzo-18-crown-6 (DВ18С6) as a structure-directing agent and titanium tetrabutoxide (TBOT) as a source of titanium in the presence of HCl with (or without) subsequent hydrothermal treatment (HTT) and calcination at 500 oC. It has been shown that the addition of a small amount of dodecyldimethylethylammonium bromide (DDMEABr) and/or lanthanum salts in ZGRM, as well as HTT, has a significant effect on the phase composition and texture of the samples. It was established that the use of HTT before calcination of samples significantly increases their photocatalytic activity (PhA) in the reaction of photocatalytic hydrogen release from an aqueous-ethanol mixture mainly due to changes in their phase composition. The hydrothermally treated sample of the anatase (85%)/rutile (4%)/brookite (11%) phase composition shows the highest photocatalytic activity, which is 2.5 times higher than the corresponding characteristic for the commercial Evonik P25 photocatalyst. It is shown that the size of the specific surface area of the sample is not the dominant factor influencing the photocatalytic activity of the obtained mixed-phase meso-nc-TiO2 samples in the process of hydrogen release from the aqueous-ethanol mixture.