The thesis is devoted to the obtaining of nanocomposites based on titanium (IV) oxide doped with oxides of rare earth metals (Sm3+, Er3+, Pr3+, Nd3+) and/or tin (IV) oxide, the study of their physicochemical properties and efficiency in the photocatalytic degradation and mineralization of antibiotics ciprofloxacin and sulfamethoxazole under artificial sunlight.
The paper considers the effect of parameters (pH, temperature, solvent type, precursor type) of various synthesis methods (sol-gel, hydrothermal, combined sol-gel-hydrothermal, solvothermal) on the photocatalytic activity of titanium (IV) oxide powders. Studies of titanium (IV) oxide samples synthesized by various methods show that the methods used allow obtaining of nanostructured TiO2, and the highest efficiency in the photocatalytic degradation of ciprofloxacin in UV light (365 nm) is revealed by the sample synthesized via hydrothermal method from titanium (IV) isopropoxide at a low temperature (110 ℃) using 2-propanol as a solvent. The obtained sample removes 99,5 % of ciprofloxacin in 120 minutes of the process, is characterized by a high specific surface area (315 m2/g) and high porosity.
It was established that after doping commercial P25 TiO2 photocatalyst and titanium (IV) oxide synthesized by hydrothermal method with oxides of rare earth metals (Sm3+, Er3+, Pr3+, Nd3+) via hydrothermal method, samples of TiO2-Sm2O3 composition show the highest photocatalytic activity. The most effective in the photocatalytic degradation of ciprofloxacin in artificial sunlight is the sample of synthesized TiO2 doped with Sm2O3 (1 wt.% Sm), which removes 94 % of the antibiotic in 30 min, and in the mineralization of ciprofloxacin – a sample of the commercial photocatalyst P25 TiO2 doped with Sm2O3 (1 wt .% Sm), which mineralizes 86,5 % of the antibiotic in 6 hours. Both photocatalysts demonstrated better results than the commercial P25 TiO2 sample. The products of the photocatalytic process with TiO2 samples doped with samarium (III) oxide did not show toxicity towards bacteria E. coli, in contrast to the commercial P25 TiO2 sample, which demonstrated toxicity after 6 h of the process.
In the photocatalytic degradation and mineralization of the antibiotic sulfamethoxazole, commercial sample P25 TiO2 showed the best activity, removed 75 % of the antibiotic in 1 h, and allowed reaching of 88 % mineralization in 3 hours. Both the products of the photocatalytic process and the initial model solution of sulfamethoxazole did not show toxicity against E. coli, which may indicate that antibacterial resistance had been already developed by E. coli.
The study of optical properties of titanium (IV) oxide doped with oxides of rare earth metals confirms a decrease in the band gap of samples based on commercial P25 TiO2 (Eg = 3,33 eV) by 0,06-0,09 eV, which contributes to the increase in photocatalytic activity. At the same time, TiO2 sample synthesized by hydrothermal method and doped samples based on it have a smaller band gap (3,27 eV), which does not change after doping.
X-ray powder diffraction analysis of pure TiO2 and TiO2 doped with Sm2O3 showed that the obtained materials were nanocrystalline. Phase composition of the samples based on P25 TiO2 is represented by a mixture of anatase and rutile with a large crystallite size (15-23 nm), while samples based on HT TiO2 consist of a mixture of anatase and brookite with a small crystallite size (4-7 nm). Using scanning electron microscopy, it was established that doping with rare earth metals does not change the morphology of TiO2. At the same time, the results of energy dispersive X-ray mapping and X-ray photoelectron spectroscopy confirm the formation of Sm2O3 layer on TiO2 surface. The method of low-temperature adsorption-desorption of nitrogen made it possible to establish that samples based on synthesized titanium (IV) oxide had higher specific surface area (202-220 m2/g) than the samples based on commercial sample P25 TiO2 (57-61 m2/g) and, as a result, better adsorption properties.
Photocatalysts of TiO2-SnO2 composition, obtained from SnCl2×2H2O precursor during synthesis, had the highest efficiency in the photocatalytic degradation of antibiotic ciprofloxacin under ultraviolet light. Doping of a commercial P25 TiO2 photocatalyst with tin (IV) oxide or samarium (IV) oxide or both oxides at the same time did not lead to an increase in the efficiency of mineralization of ciprofloxacin under artificial visible light. On the contrary, doping of the synthesized titanium (IV) oxide with samarium (IV) oxide or tin (IV) oxide and samarium (IV) oxide simultaneously lead to the increase in the efficiency of mineralization of ciprofloxacin, especially in visible light range. It was established that the efficiency of mineralization of ciprofloxacin by a photocatalyst based on the synthesized TiO2 with 1 wt.% Sm is 5 % higher in visible light compared to the commercial sample of EVONIK AEROXIDE TiO2 P25.
