The Behavior Of Nitrogen Fixation In TiCl₄/Alcohols System And Its Application For Preparing Nano Titanium Dioxide Photocatalysts

Semiconductor titanium dioxide?TiO₂?as an important titanium compound has been regarded as one of the most promising photocatalysts to solve the problems of worldwide energy shortage and environmental pollution owing to its superior physical and chemical properties?nontoxicity,stability,controllable crystal phases and suitable wide-band-gap?.However,solar energy contains only about 4-5%UV light on the surface of earth,strong efforts are being made to shift its photocatalytic activity to the visible spectral region.Among the various methods for preparing nano-TiO₂ photocatalysts,TiCl₄/alcohols system has been widely used.Nevertheless,many researchers only payed more attention on the characteristics of the composition,structure and morphology of as-prepared TiO₂,the changes of reaction process in system has been always ignored.In this dissertation,an intensive study has been carried out to deal with the above problems.The behavior of nitrogen fixation in-TiCl₄/alcohols systems was accidentaly discovered to prepare the?NH4?0.3TiO1.1F2.1 crystal.By investigating the mechanism of nitrogen fixation,a green synthesis route for synchronous inorganic-organic reaction could be obtained to prepare the ketones,ethers and halohydrocarbons from alcohols,based on the TiCl₄/alcohols systems.Furthermore,the N-doped anatase TiO₂ nanosheets could be prepared by the pyrolysis of as-prepared?NH4?0.3TiO1.1F2.1 productions;And the novel mixed-halide titanium??,??compound single crystal could be synthesized from the final mixture organic productions.Finally,the TiCl₄/alcohols system could be further employed to preparing nano-TiO₂ photocatalysts.The main contents are as follows:1)Thesis part ? is a foreword part,brifly summarizing the research significance,latest progress and preparation methods of TiO₂.And the deficiency of the research at present are produced.Emphatically,the basis and research emphasis of thesis topic are presented.2)The chapter ? mainly introduces all experiment instruments and characterized equipments in this thesis.3)The chapter ? mainly presents the new discovery that the behavior of nitrogen fixation in TiCl₄/alcohols systems was carried out by using isopropanol as a solvent in the presence of HF,and the non-stoichiometry ammonium oxofluorotitanates??NH4?0.3TiO1.1F2.1?crystal was successfully prepared.Based on the isotopic labeling experiments with labeled 15N2 gas and combining relevant characterization analyses with theoretical calculation,it is confirmed that the TiCl₄ solution can adsorbe the dissolved nitrogen and further formed a homogeneous Ti-based complex in isopropanol solvent through alcoholysis,which could result in the formation of?NH4?o.3TiOi.iF2.i crystal by converting N?into ammonium or ammonia.Meanwhile,the nitrogen fixation of TiCl₄ could be carried out to preparing the?NH4?0.3TiO1.1F2.1 crystal by using other alcohol solvents replacing the isopropanol.4)The chapter ?mainly presents the mechanism of nitrogen fixation of TiCl₄/alcohols systems.Based on the fact that the?NH4?0.3TiO1.1F2.1 crystal could be prepared by nitrogen fixation of TiCl₄/alcohols systems in the liquid phase,through isotopic labeling experiments and further blank contrast experiments,the final productions are characterized by using NMR,GC-MS and XRD technologies.Results revealed that the behavior of nitrogen fixation of TiCl₄/alcohols systems not only could be used to prepare inorganic?NH4?0.3TiO1.1F2.1 crystal,but also could be applied to synchronously achieve catalytic oxidation of organic solvent.A possible reasonable mechanism was proposed that the protonation of Ti-N complexes contributed to weaken the bond energy of N=N into N=N,and it was further converted into ammonium or ammonia resulting from the cleavage of N-N.In addition,a homogeneous mixture containing ethers and halohydrocarbons could be obtained due to the recombination of alkyl and alkoxy groups.5)The chapter ? mainly introduces the mixed-halide titanium??,??compound?Ti2F6Cl?single crystal could be prepared from the homogeneous mixture production derived from the nitrogen fixation of TiCl₄,via a route of constant temperature incubation after several months.Its structure was further structurally characterized by single-crystal X-ray diffraction.It crystallizes in the orthorhombic space group Pnma?No.62?with a = 9.314?4?,b = 5.493?2?,c = 9.762?4?A,Z = 4 and V=499.4?3?A3.Its structure features[Ti2F6]+ polyhedral-constructed a 3D network.The lower transformation ratio of Ti could be resulting from the existence of[Ti2F6]+ species.6)The chapter ? is presented that the as-prepared?NH4?0.3TiO1.1F2.1 crystal could be used as precursor of N-doped TiO₂ nanosheets by annealing treatment under different atmospheres.The non-stoichiometry ammonium oxofluorotitanates crystal with layer by layer self-assembly morphology could be converted into N-doped TiO₂ nanosheets containing different content of N dopant.The resultant N-doped TiO₂ nanosheets exhibit an enhancement of visible-light-driven photocatalytic activity and a higher electrochemical performance due to its good ordered layer structure,high content of N dopant and its high crystallinity,large surface area and fast spacial separation of photoinduced charge carriers.7)The chapter ? mainly discusses the formation progress of monodisperse flower-like anatase TiO₂ microspheres with active facet exposed from TiCl₄/alcohols systems in the presence of PVP.And it icould be further employed as catalyst supporter to prepare the monodisperse quantum-sized BiVO4 nanotubes decorated flower-like anatase TiO₂?BiVO4@TiO₂?composite photocatalysts.By contrast,the as-prepared monodisperse TS-BiVO4@TiO₂ composites samples exhibited a higher photocatalytic activity than that of OS-BiVO4@TiO₂ composites samples,which could be attributed to the effective separation of photoelectrons from vacancies and the exposed active facet of TiO₂.8)The final chapter ? further discusses the application of Ti-based complexes from TiCl₄/alcohols systems.A series of Bi-doped anatase TiO₂ hollow thin sheets samples with 001}facets exposed have been fabricated by a simple one-pot hydrothermal synthesis route,mixed with BiVO4 precursor.Controlling BiVO4 precursor concentration plays a key role in tuning the morphology and the Bi doping concentration of TiO₂ hollow thin sheets catalysts.The photocatalytic activity of as-prepared catalysts was evaluated through the photo-degradation of different organic dye under visible light irradiation?>400 nm?,including methylene blue?MB?,methyl orange?MO?,Rhodamine-B?RhB?and p-nitroaniline?PNA?.Results showed that the optimal dopant of 0.8 at%Bi in TiO₂ achieved the best photocatalytic activity especially for possessing a much higher photodegradation of PNA,which could be ascribed to the results of photoinduced charge separation and transfer combined with low bulk recombination of charge carriers.This discussion demonstrates that the design of new TiO₂ nanostructures for application in solar energy conversion could be easily achieved by coupling Bi cation-doping and active facets with hollow thin sheets morphology.