Defective TiO₂ Composite Material Preparation And Performance

TiO₂,an environmentally-friendly photocatalyst,has several advantages including low cost,stable chemical properties,and a simple production process.However,its high photoinduced charge carrier recombination rate and narrow light absorption range limit its photocatalytic efficacy.Research has revealed that utilizing defects to regulate the band structure of TiO₂ can enhance light absorption and reduce the recombination of photocarriers.Conductive metal-organic frameworks（MOFs）,as a unique electronic material,stand out in the field of photoelectrochemistry due to their high conductivity,large surface area,and broad spectral response.Hence,this thesis investigates the application of conductive MOFs combined with defective TiO₂ in the field of photocatalysis.The contents are as follows:（1）Oxygen-deficient TiO₂(TiO_2-x)was prepared by the solvothermal method,and then the Ni₃（HITP）₂/TiO_2-x composites were prepared by hydrothermally loading the conductive MOF material Ni₃（HITP）₂.The structure and morphology of the composite material were characterized and analyzed by a series of techniques,including XRD,FT-IR,and SEM,while the light absorption properties of the composite material were studied via UV-Vis diffuse reflectance spectroscopy.Under visible light（λ>420 nm）,the degradation efficiency of Rhodamine B by 3 wt.%Ni₃（HITP）₂/TiO_2-x-2 reached 99.1%in 50 min,with a reaction rate constant 5.2 times that of TiO_2-x-2.The hydrogen evolution rate of 3 wt.%Ni₃（HITP）₂/TiO_2-x-2 under simulated solar light was 5.804 mmol/g/h,which is 2.73 times that of TiO_2-x-2.The apparent quantum yield and energy conversion efficiency were 5.741%and 0.352%,respectively.The composite material also exhibited stable and efficient performance after four use cycles.The reaction mechanism of Ni₃（HITP）₂/TiO_2-x was studied through free radical capture experiments and photoelectrochemical testing,and the feasible charge transfer pathway of the heterojunction structure of Ni₃（HITP）₂/TiO_2-x was proposed.It was determined that a z-scheme Heterojunction was formed between Ni₃（HITP）₂ and TiO_2-x,which was the main factor responsible for the improved photocatalytic performance of the composite material.（2）Ni₃（HITP）₂/Ti_1-xO₂ composites were prepared by introducing Ni₃（HITP）₂ into titanium-deficient TiO₂(Ti_1-xO₂)by hydrothermal method.The composite material’s structure,morphology,composition,and optical absorption properties were tested using characterization techniques such as XRD,TEM,XPS,and UV-vis diffuse reflectance spectroscopy.It was found that 4 wt.%Ni₃（HITP）₂/Ti_1-xO₂-2 achieved a 93.8%degradation efficiency of Rhodamine B in 50 minutes under visible light,with a rate constant that was5.56 times of the Ti_1-xO₂-2 sample.The hydrogen evolution rate under simulated solar light was 3.52 mmol/g/h,which was 2.1 times that of the Ti_1-xO₂-2 sample.The apparent quantum efficiency and energy conversion efficiency were 3.96%and 0.23%,respectively.The experimental results and characterization analysis verfied the successful construction of the z-scheme Heterojunction of Ni₃（HITP）₂/Ti_1-xO₂ composite material,which suppressed the recombination of photogenerated carriers and maintained the excellent redox potential of each material.This is the main reason for the improvement of the composite material performance.