Destruction of some dyes on composite photocatalysts based on SiO2/TiO2 oxides

The composite SiO2/TiO2 oxides were obtained from precursors with different molar ratios of silicon and titanium in the initial solution.Samples were prepared in two stages. The first stage was based on sol-gel technology using hydrogen peroxide as a complexing agent. Titanium oxyhydroxide was conventionally precipitated, washed with double-distilled water and redissolved in hydrogen peroxide to form peroxotitanic acid. A non-opalescent transparent solution was formed. Sodium silicate was added to this solution for the formation of the united molecular precursor. After hydrolysis of this precursor a composite sample was obtained in which TiO2 grains were encapsulated in a SiO2 matrix. In the second stage, the prepared material was treated under hydrothermal conditions in autoclaves at self-regulating pressure. TiO2 was crystallized in the form of grains, approximately 10 nm in size. Processes of crystallization and crystal growth were controlled by the amorphous silicate matrix. The small grain size of TiO2 led to high photocatalytic activity of the material. Samples were studied by powder X-ray diffractometry and scanning electron microscopy. Photocatalytic activity was determined for all obtained samples in the decomposition reaction of methylene blue under ultraviolet radiation. The highest degree of substrate degradation was reached by the sample with SiO2/TiO2 ratio equaling 1:2. The possibility of photocatalytic destruction of methyl orange and methylene violet was determined for this sample. Methyl orange was decomposed rather slowly by this photocatalyst, unlike methylene violet and methylene blue. The resulting photocatalysts can be used to purify water from dyes.