Design,Synthesis And Photocatalytic Characterization Of Boron And Transition Metal Co-doped TiO₂

Among various semiconductor photocatalysts,TiO₂ has attract great interests due to its low cost,chemical inertness,photostability,and non-toxicity.However,the wide bandgap?Eg=3.2 eV?and high electron-hole recombination rata of TiO₂ result in the low photocatalytic efficiency and prevent its practical applications.In this thesis,we prepared the non-metal?B?and transition metal?M=Zr,Ta,Y?co-doped TiO₂ by a sol-gel method,and evaluated the photocatalytic performance of all the samples by photo-decomposition of methylene blue?MB?solution.XRD,Raman,SEM,BET,XPS,UV-vis measurements were performed on all the samples to investigate the effect of codoping on the structural,electronic,and optical properties of TiO₂ nanoparticles,and the mechanism for the enhanced photocatalytic activity.The content of this thesis can be divided into three sections.Firstly,we studied the effect of B-Zr co-doping on TiO₂ photocatalysts.Based on the results of decomposition methylene blue?MB?solution,it is found that B and Zr codoping can raise the photocatalytic performance of TiO₂ by a fold.Experiemental results indicate that the enhancement of photocatalytic activity can be attributed to the following factors: 1)doping can inhibit the growth of TiO₂ nanocrystal and increase the surface to volume ratio;2)B tends to occupy the interstitial sites,creating oxygen vacancies?Ov··?and reducing Ti⁴⁺ to Ti³⁺ to form [Ov··-Ti³⁺]⁺,which traps the carriers and prolongs carrier lifetime;Zr⁴⁺ ions will replace Ti⁴⁺ ions and form impurity levels,which could improve visible light response.Secondly,we studied the effect of Ta mono-doping and B-Ta co-doping on TiO₂ photocatalysts.It is observed that all the doped samples have improved photocatalytic activity while B-Ta codoped TiO₂ has the highest efficiency on decomposition of MB solutions.Similary to the previous section,B and Ta doped samples also have smaller crystallite size and thus larger surface-to-volume ratio than the undoped one.Moreover,boron also stays at the interstitial site of TiO₂ crystal.However,Ta doping do not result in dramastic increase of visible light absorption.It is found that Ta⁵⁺ ions tend to replace Ti⁴⁺ ions which would increase the electron density and creates oxygen vacan cies.The third part of this thesis is focused on Y mono-doped and B-Y co-doped TiO₂ photocatalyst.B-Y co-doped samples exhibit better photocatalytic performance than undoped TiO₂ but Y-doped samples do not have pronounced improvement,indicating a synergestic effect lead to the surperior photocatalytic activity of B-Y codoped TiO₂.Similar to the B-Zr and B-Y doped samples,B and Y doping increased the surface-to-volume ratio of TiO₂ nanocrystal.Boron ions also stay at interstitial sites and prolonged the carrier lifetime.Y tends to substitute Ti and existed in the form of Y³⁺.The Y single doped TiO₂ would harmful for photocatalysis property.