Abstract
The experimental results obtained in the study on the possibility of sensitizing titanium dioxide (polymorphic anatase phase) to the visible region of the spectrum by doping and co-doping with impurities of non-metals in order to create effective photocatalysts for the decomposition of organic compounds have been analyzed. The presence of impurity atoms appears to result in a change in the electronic structure of the titanium dioxide matrix, in the appearance of “impurity bands” and in the narrowing of the energy gap of titanium dioxide. Such a modification is accompanied by an extension of the spectral range of sensitivity of photoactive solids to the long-wavelength region of the spectrum and, therefore, can be used to improve the catalytic properties of these materials. Spectral manifestations of carbon impurities in titanium dioxide in the form of carbide and carbonate, as well as sulfur in the forms of sulfite, sulfide, and sulfate, have been studied by the density functional theory method. A Ti14H22O39 cluster model was chosen for the titanium dioxide matrix. The calculations were carried out in the framework of the cluster approximation, using functional B3LYP and basis set 6-31G (d, p). Comparison of the results of quantum chemical calculations with the available experimental data shows that the impurity sulfur and carbon atoms in titanium dioxide, which are in different coordination states and different oxidation states, appear in different spectral ranges. This circumstance makes it possible to elucidate the structure of the samples based on the experimental spectra. A change in the coordination and oxidation states of impurity atoms leads to spectral shifts and splitting of peaks, which can reach 1.5 eV (XPS). The presence of admixtures of non-metals leads to a change in color (deepening in the case of sulfide or carbide) of the samples, appearing in the corresponding UV spectra.
Highlights
Examination of nanoparticles, their ensembles and nanocomposites based on a number of wide-gap metal oxides has acquired particular relevance in recent years in connection with a number of properties of such objects that are interesting from a scientific and practical point of view
Different oxidation states of non-metal atoms were taken into account, so there can be carbide and carbonate, sulfide and sulfate structures incorporated into the bulk of titania nanoparticles (Fig. 1)
We considered cluster models of TiO2 containing sulfur atoms in different oxidation states: one and two sulfide type sulfur atoms, sulfite and sulfate groups in the anatase structure
Summary
Examination of nanoparticles, their ensembles (powders) and nanocomposites based on a number of wide-gap metal oxides has acquired particular relevance in recent years in connection with a number of properties of such objects that are interesting from a scientific and practical point of view These are, in particular, their specific photoactivity, which appears as photostimulated formation and annealing of optically active defects (photostability and photosensitivity, photochromism) of oxide materials; photostimulated molecular transformations on the surface of dispersed solids, being a base of so-called heterogeneous photocatalysis, promising for converting solar energy into chemical one and for purifying water and air from pollutions, etc.; photoelectronchemical conversion of solar energy [1].
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