Tunable Structure And Enhanced Photocatalytic Oxidation Performance Of Inorganic And Organic Semiconductor Materials

The increasing number of harmful substances and toxic gases emitted by humans to the water and atmospheric environment have caused very serious environmental problems.The emergence and development of photocatalytic oxidation technologies are expected to alleviate environmental pollution.At present,there are many problems in the semiconductor materials,such as the easy recombination of charge carriers and poor thermal stability.These defects inhibited their photocatalytic activity and were not favorable to their practical applications.In this paper,we have enhanced the photocatalytic oxidation capabilities of various semiconductors by regulating their structural properties,such as morphology,phases,energy bands,and defects.The main content and results were listed as follows:Section 1:In view of the low thermal stability of TiO₂,whose phase-transition temperature was only 600°C,we introduced fluorine into the tetrabutyl titanate to prepare the precursor TiOF₂ by the hydrothermal method,and then prepared a oxygen-vacancy contained TiO₂ with high thermal stability by calcination.The effect of calcining temperature on the photocatalytic performance of the prepared TiO₂ for toxic acetone oxidation was carefully explored.The results show that the phase transition of TiO₂ did not occur until the calcination temperature was up to 1000°C.This is because fluorine element volatilized at high temperature and oxygen vacancies were introduced,which prevented the TiO₂ particles from growing up quickly and improved the thermal stability of TiO₂.By comparing the photocatalytic oxidation activities of acetone over the calcined materials at different temperatures,we found that the optimum calcining temperature was at 500°C,and the acetone removal was102.5 ppm,which was 4.9 times higher than that of the sample calcined at 1200°C.This is due to the fact that surface fluorine not only successfully induced the formation of highly active?001?crystal plane,but also changed the formation state of hydroxyl radicals.Section 2:Aiming at the shortcomings of the inorganic BiVO₄ semiconductor material,in which photogenerated carriers are easy to recombine,we adjusted the pH of the solvent with ammonia and used hydrothermal method to prepare BiVO₄ with controllable morphology and crystallinity.The obtained samples were applied in photocatalytic degradation of Rhodamine B in water.The results showed that with increasing pH value,the crystallinity of BiVO₄ increased,and the morphology became relatively uniform and tended to be more regular.When the pH value increased to 11,the crystallinity of BiVO₄ reached highest and its morphology was a sharp-edged polyhedron.At this time,the photocatalytic activity of the material was the best.The degradation rate of Rhodamine B was as high as 85.9%,which was 4.2times higher than that of sample prepared at pH=1.The reason for the enhancement was that the carrier separation efficiency of BiVO₄ was getting better as the pH value increased.Section 3:For the shortcomings of organic semiconductor graphite phase C₃N₄?g-C₃N₄?,in which photogenerated carriers were easy to recombine,we used the combination of hydrothermal and calcining methods to prepare the carbon-defect contained g-C₃N₄,and applied it for photocatalytic nitric oxide oxidation.The results showed that:?1?The added urea during the hydrothermal process served as a morphology-directed agent to prepare the tubular g-C₃N₄;?2?Changing calcining temperature can optimize the valence and conduction band position.When the calcination temperature was 500°C,the conduction band position of g-C₃N₄ was the most negative,and the nitric oxide removel performance was the best,with the removal rate of 43.4%.?3?The nitrogen calcination atmosphere was favorable to form the carbon-defect contained g-C₃N₄,improving its carrier separation efficiency and enhancing its adsorption capacity for the reactant molecules.The nitric oxide oxidation activity of the sample obtained in a nitrogen atmosphere was 2.6 times higher than that of the sample obtained in air atmosphere.