Structure and Properties of Visible-Light Active  Binary TiO₂ & Au Nanocomposites

Today, the creation of new and improvement of existing photocatalytic nanomaterials is one of the most urgent tasks of modern materials science. In particular, titanium dioxide-based photocatalysts have been successfully used to degrade organic dyes, but require exposure to visible light, which is explained by the semiconductor's wide band gap of 3.2 eV. One way to extend the action of titanium oxide catalysts to the visible light region is to modify them with substances of a different nature, such as noble metals. We have carried out a chemical synthesis of binary nanocomposites based on TiO2 modified with gold in the range of dopant concentration from 0.5 to 3.5 wt%. Titanium tetraisopropoxide was chosen as a titanium oxide precursor compound, and aurum aquaforms were obtained from a solution of gold hydrofluoric acid. The composition, structure, and morphology of nanocomposite particles were determined and their photocatalytic activity was tested under visible light for the destruction of malachite green (MG). The initial dye solution contained 20 mg/dm3 of MG at a pH of 6.8. By X-ray phase analysis, it was found that calcination of all lyophilized titanium-aurum-containing precipitates at T 600 C leads to the formation of anatase particles, and an increase in the treatment temperature to 1000 C promotes only a partial polymorphic transformation of anatase into rutile. The calculation of the crystal lattice parameters of anatase suggests that gold forms clusters on its surface. At the same time, it is possible that aurum cations may partially enter the anatase lattice, which requires further investigation. The size of anatase particles varies from 9.2 to 12.3 nm, and the size of rutile particles reaches 35 nm. Photocolorimetric measurements of the degree of destruction of the MG were performed according to the standard method after the system reached equilibrium for 30 minutes of stirring the suspension in the dark. A centrifuge with a capacity of 8 g was used to precipitate the nanoparticles in order to prevent their influence on the measurement results. The results proved that all samples of gold-modified anatase have a high efficiency of solution decolorization, which is 88-95% within 10-20 minutes. The best result was obtained for the sample with a 2 wt.% admixture content. The decolorization efficiency decreased to 45-53 % after heat treatment of the samples at T 1000 C. Further studies of particles of nanocomposites based on titanium dioxide modified with gold will be aimed at determining the effect of pH and dye concentration on the efficiency of its destruction. Attention will also be paid to the possibility of regeneration of the composite particles and evaluation of their stability under the influence of the dye. It is also planned to make a comparative characterization of the effectiveness of particles of coated composites under the influence of UV irradiation and visible light regarding the destruction of MG solution