The effect of nanosized porous films (average density 10 g/m 2 ) of TiO 2 . TiO 2 /SiO 2 , and SiO 2 on the photostability of adsorbed methylene blue (MB) dye during UV irradiation in air was investigated by optical spectroscopy and laser-induced mass spectrometry. The effectiveness of the photodecomposition of MB decreases in the order TiO 2 > TiO 2 /SiO 2 > SiO 2 with rate constants 1E-2, 0.6E-2, and 0.3E-2 min -1 respectively. A mechanism including the participation of both excited states of the dye molecules and photoexcited titanium dioxide is proposed for the photodecolorization of MB adsorbed on the surface of the investigated films.Acridine, xanthene, thiazine, triphenylmethane, and other dyes that absorb visible light and have bright colors are of enormous scientific and technical interest on account of their use in chemical and biological processes, laser technology, optical data processing, creation of light-resistant systems, textile industry, etc. At the same time dyes are some of the most widespread contaminants of the environment as a consequence of their stability and consequent ineffective natural biodegradation. Heterogeneous photocatalysis using mostly TiO 2 in the anatase form ([1, 2] and the references therein) is used as an alternative to the traditional poorly effective methods for the purification of contaminated water, such as flocculation, adsorption with activated charcoal, or biopurification. The action of UV irradiation in TiO 2 leads to the generation of electron-hole pairs, which initiate the formation of active OH* radicals capable of decomposing the majority of organic compounds in solutions. The overwhelming majority of publications on the photodegradation of dyes by titanium-containing catalysts have been devoted to analysis of the photocatalysis processes in aqueous solutions, and rhodamines (6G or B) or methylene blue (MB) have often been used as model dyes. Insufficient attention has been paid to study of the state of adsorbed molecules of the dye and its photodegradation at the surface of the photocatalysts in the absence of a solvent [3,4]. In the mean time this problem is urgent not only from the standpoint of the investigation of adsorption as the initial stage of photocatalysis (most authors do not discuss the fate of the dye molecule at the surface of the photocatalyst at all, although it is the surface that has a great effect on the kinetic of the process at the early stages) but is also of independent importance during the design of optical cells with controllable spectral characteristics. The tendency of the adsorbed molecules of dyes to associate and aggregate also affects their photostability and capacity for photodegradation.Earlier we recorded for the first time the calcination fine-structure fluorescence spectra of aromatic hydrocarbons adsorbed on silica with selective laser excitation in the region of the 00 transition at low temperature and detected reversible 0040-5760/07/4304-0235

The efficiency of nanosized mesoporous TiO

Electronic spectra and LDI mass spectra changes accompanying photodegradation of acridine yellow (AY) adsorbed on the surface of prepared via templated sol-gel synthesis TiO 2 , SiO 2 , and TiO 2 /SiO 2 mesoporous films have been investigated and the main photodegradation products have been determined. The results of calculations show the adsorption energy of the molecular state of AY to be the greatest for the complex with titania-silica where Lewis acidic sites are present, the smallest one being related to the complex with titania what corresponds to the experimental data. Effectiveness of acridine yellow photodegradation on the surfaces of mesoporous films under UV irradiation increases in a row SiO 2 \ TiO 2 /SiO 2 \ TiO 2 . Electronic and laser desorption/ionization mass spectra and theoretical modeling give evidence that efficient photobleach of AY localized at the surface of anatase films proceeds through the following steps: 1-N-demethylation/deamination; 2-photodimerization; 3-photodegradation.