Preparation And Spectroscopic Characterisation
PREPARATION AND SPECTROSCOPIC CHARACTERISATION
OF NANOSIZED TITANIA - SILICA PHOTOCATALYSTS VIA PHOTOINDUCED ELECTRON TRANSFER PROCESSES
OF ADSORBED ORGANIC FLUOROPHORES
A. Eremenko, N. Smirnova, O. Linnik, O. Yakimenko, O. Chuiko
Institute of Surface Chemistry of National Ukrainian Academy
of Sciences, Kiev, Ukraine, e-mail: annerem@mail.kar.net
Titania-silica mixed oxide materials are important as photocatalysts and catalysts support materials. The sol-gel synthesis is expected to offer unique advantages for the preparation of highly dispersed and transparent active thin-film photocatalysts. Therefore, it is of special interest to study the role of the local interaction of adsorbed molecular probes with surface active centres as well as with titania particles placed into silica porous matrices. Fluorescent spectroscopy and nanosecond time-resolved diffuse-reflectance laser flash photolysis is used to study photoinduced ET reactions of the acenes a. g. pyrene and pyrenemethanole adsorbed on the titania-silica surfaces and to determine the effect of titania particles on the processes of its adsorption and radical cations formation.
In this study, we concentrated on the preparation of highly transparent TiO2 and TiO2 /SiO2 ( 0.1 - 50 wt % of titania) films and powders using the sol-gel method and the characterization of these systems by means of fluorescence spectra of adsorbed pyrene (Py), pyrene-methanole (PyMe). Organic molecules are adsorbed strongly on the TiO2 and Ti/Si surfaces. Increasing of Ti content within Ti/Si systems results in decrease of the intensity of the photoluminescence spectra. Fluorescence of Py excimer is suppressed if Ti is present in silica matrices. In contrast, PyMe molecules adsorbed on Ti/Si films demonstrate a new broad structureless emission in the visible region belonging to the associates, with increasing of Ti content in the film from 0.3 to 3%. These changes in spectra indicate that an interaction between PyMe and Ti/Si surface occurs. High polar PyMe molecules are easily adsorbed onto Ti/Si surface due to hydrogen bonds. The fluorescence
emission quenching can be attributed to the charge injection from the singlet excited state of the molecule to the conduction band of semiconductor. When Ti content increased ions paire - PyMe cation-radical and Ti3+ ions was formed under impulse laser irradiation on the mixed silica-titania systems due to direct interaction PyMe molecules with TiO2 nanoparticles.
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