Study On The Design And Regulation Of Defect Titanium Oxide And Its Catalytic Properties

TiO₂ is the earliest and most widely studied semiconductor oxide in the field of photocatalysis.Its physical and chemical properties?such as photoabsorption,adsorption,electron transport and transfer,catalytic activity,etc.?are closely related to its structural defects.The existence of defects can obviously broaden the spectrum response range of TiO₂ photocatalyst and improve its quantum efficiency which make the materials have better catalytic performance.In this paper,the structural defects of TiO₂ photocatalysts were studied,including the design and control of the structural defects of photocatalysts.The morphology and structure of the obtained materials were characterized and analyzed by a series of methods,such as XRD,TEM,XPS,ESR,XAFS,etc.The visible light degradation activity of defective TiO₂ was investigated.In addition,efficient noble metal supported catalysts were designed and synthesized via an in situ redox reaction and used in diverse catalytic reactions.Such as photocatalytic degradation,thermal catalytic CO oxidation,photocatalytic dehydrogenation of benzyl alcohol and photocatalytic coupling dehydrogenation of acetonitrile,etc.This paper can be divided into the following three parts:In the first part,anatase TiO₂ nanocrystals with structural defects were successfully synthesized by simple chemical precipitation method and further treated in different atmospheres.The XPS and ESR spectra show that the oxygen vacancy?V_O?and the Ti³⁺defects exist simultaneously in the sample calcined in N₂?N-TiO₂?,while V_O defects are mainly found in the sample calcined in air?A-TiO₂?.The studies of photocurrent-responsive,SPV and PL show that A-TiO₂ has a higher separation efficiency of photogenerated carriers,which does not match its weak light absorption in the visible region.The enhancement of A₃ peak intensity in EANES spectra combined with the increase of Debye-Waller factor confirmed the existence of structural distortion in the main body of the two samples.Due to the electron delocalization on several Ti ions,A-TiO₂ has a low coordination Ti,which can effectively activate oxygen molecules,so it has excellent photocatalytic degradation activity under visible light irradiation.In addition,the electrons at the defects can reduce the noble metal ions,so the distribution of the nucleation sites and the particle size can determine the distribution of defects on the surface of the catalyst.The supported catalyst prepared by this method was not only beneficial to the charge transfer in the catalytic process,but also to the stability of the catalyst because of the close combination between the metal particles and the support.Zeta potential of the sample with a short reduction time is negative due to the transfer of electrons from support to the metal.This is beneficial to the adsorption and activation of reactants,thus improving their visible photocatalytic activity,but not conducive to the thermal catalytic oxidation of CO.The second part of the work realized the oxidative dehydrogenation of benzyl alcohol via photocatalytic technology.Light energy was the driving force of the reaction.The supported noble metals?Au and Pt?can not only capture photogenerated electrons to promote the separation of holes and electrons,but also act as active centers to promote the dehydrogenation of benzyl alcohol molecules.Compared with the traditional thermal catalytic oxidation of benzyl alcohol,the photocatalytic process is more economical and efficient.By designing different supported catalysts,the active species in the reaction were successfully regulated and the reaction process was changed.Thus the oxidation activity of the catalyst and the selectivity of the product were improved.For Au_0.5-P25,the active specie of benzyl alcohol oxidation was mainly superoxide free radical,while the main active species of bimetallic catalyst is the photoinduced hole.Compared with monometallic supported catalysts Au_0.5-P25 and Pt_0.5-P25,bimetallic supported catalysts Au_0.25-Pt_0.25-P25 have a higher efficiency of photocatalytic oxidation dehydrogenation of benzyl alcohol.The final product of aerobic selective oxidation of benzyl alcohol is benzaldehyde and water,while the final product of anaerobic oxidation of benzyl alcohol is benzaldehyde and hydrogen.So anaerobic oxidation of benzyl alcohol is more economical.In the third chapter,the C-H bond in acetonitrile molecule was successfully activated realized the dehydrogenation self-coupling by photocatalytic technique.The reaction was carried out at room temperature and atmospheric pressure.To avoid the use of toxic reagents or solvents,only CH₃CN was used in the reaction which acted as both reactant and solvent.Light energy was the driving force in the self-coupling reaction.The supported noble metal Pt can not only capture the electrons to promote the separation of holes and electrons,but also act as the active center to promote the dehydrogenation of acetonitrile molecules.The presence of oxygen was not conducive to the dehydrogenation of acetonitrile,while the presence of a small amount of water in the solution can greatly promote this reaction.The active species in the reaction process were mainly the photogenerated electrons migrated to the platinum surface.When the hydroxyl radical and the photogenerated hole were trapped,the activity of coupling reaction could be further improved.