Preparation,Photocatalytic Performance And Formation Mechanism Research Of TiO₂

With the worldwide environmental pollution and ecological destruction,people pay great attention to clean production without pollution.Photocatalytic as a highly efficient,energy-saving and green environmental protection technology has received increasing attention from various countries.Among numerous photocatalysts,nano-TiO₂ is widely used in wastewater treatment,atmospheric purification,and self-cleaning coatings due to its high photocatalytic activity,good chemical stability,and low toxicity.However,TiO₂ has a wide band gap and the photo-generated carriers are easily recombined,which limits its wide application.Therefore,how to effectively improve the photocatalytic efficiency of TiO₂ has become the focus of current research.In this thesis,TiO₂ was modified from the aspects of micromorphology and non-metallic N-doping to improve the photocatalytic efficiency.The effects of various process parameters on the photocatalytic performance of the products were analyzed by a series of single factor experiments.The formation mechanism of the morphology and N doping mode was also discussed.Specific work were carried out as follows:（1）Ti（SO₄）₂ and hydrazine hydrate（N₂H₄·H₂O）were used as raw materials to prepare high mesoporous honeycomb-like TiO₂ through two-step hydrothermal method and calcination.The effects of hydrazine hydrate dosage,hydrothermal temperature,hydrothermal time,calcination temperature and calcination time on the photocatalytic performance were investigated by a series of single-factor experiments.The results showed that the preparation method was less affected by the experimental conditions,and the products with high photocatalytic activity can be obtained without strictly controlling the process parameters.The obtained samples had a honeycomb mesoporous structure with spherical distribution and good dispersibility.The spherical diameter was about 18 nm,the specific surface area was 105.21 m² g^-1,and the average pore diameter was 11.12 nm.The photocatalytic efficiency of the sample degrading the methyl orange under simulated visible light was 97.09%,which was 1.8times as ordinary P25 and 2.1 times as TiO₂ without hydrazine hydrate.The formation mechanism of the sample showed that hydrazine hydrate was an important reason for the formation of honeycomb-like mesoporous and also the source of N-doped defects,which was a key factor in improving photocatalytic efficiency.（2）Ti（OH）₄ as precursor obtained by co-precipitation of Ti（SO₄）₂ and NaOH,and NH₃·H₂O was used as structure-directing agent to prepare N-doped TiO₂nanosheets.Through a series of single factor experiments,the effects of various process parameters on photocatalytic performance were studied.As a result,the best preparation condition was found as follows:the hydrothermal reaction was carried out at 180℃for 48 h with 0.8 g Ti（OH）₄,10 mL NH₃·H₂O and 20 mL deionized water.Then the sample was washed with water and calcined at 450℃for 4 h.The obtained nanosheets were well dispersible with a side length of about 100 nm,a thickness of about 5 nm,a specific surface area of 61.23 m² g^-11 and an average pore diameter of10.37 nm.The photocatalytic efficiency of the sample degrading methyl orange under ultraviolet light was 97.09%,which was 1.5 times as TiO₂ without adding NH₃·H₂O.The formation mechanism of TiO₂ nanosheets with metastable structure of titanate was obtained by ion exchange,intercalation,swelling and mechanical swinging.The embedding and peeling of NH⁴⁺was the key factor.NH₃·H₂O was a source of N doping,which was introduced into the defects by gap and alternative doping to improve photocatalytic performance.