Controllable Preparation And Photocatalytic Activity Of Titanium Dioxide Based Heterojunction

The abuse of fossil fuels resulted in serious energy shortages and environmental pollution.Therefore,it is necessary to develop clean,renewable and inexpensive energy using new technologies,which also reduces environmental pollution.The development and utilization of solar energy is particularly important.Photocatalytic technology can help alleviate the energy crisis by using solar energy to decompose water to produce hydrogen and reduce CO₂ to fuel.Among many photocatalysts,TiO₂ has attracted widespread attention because of its non-toxicity and low cost.However,the disadvantages of the low sunlight absorption efficiency resulted from the wide band gap of TiO₂ and high recombination rate of photogenerated carriers limit the extensive application of TiO₂.To solve the shortcomings in the TiO₂ photocatalytic process,in this thesis,the TiO₂ nanofibers and macroporous/mesoporous TiO₂ were first prepared by electrospinning and self-assembly method,respectively.Subsequently,the TiO₂@CaIn₂S₄ nanofibers,Cu₃（BTC）₂@TiO₂ core-shell composites and the macroporous/mesoporous TiO₂@CaIn₂S₄ were prepared by hydrothermal method.Then the photocatalytic activity and mechanism of the TiO₂@CaIn₂S₄ nanofibers,Cu₃（BTC）₂@TiO₂ and macro/mesoporous TiO₂@CaIn₂S₄ photocatalysts were further investigated.The main contents are as follows:1.TiO₂ nanofiber precursor was first prepared by electrospinning,followed by high-temperature calcination.Then,the TiO₂@CaIn₂S₄ step-scheme heterojunction photocatalysts was prepared via a hydrothermal method by using Ca（NO₃）₂·4H₂O,In（NO₃）₃·4.5H₂O,and CH₃CSNH₂ as the calcium,indium and sulfur sources,respectively.The experimental results showed that the TiO₂@CaIn₂S₄ photocatalysts exhibited a significantly light absorption range.Importantly,the photocatalytic hydrogen production performance of the TiO₂@CaIn₂S₄ is 3.2 times higher than that of the pure TiO₂ nanofibers.The S-scheme heterojunction formed at the interface between TiO₂ and CaIn₂S₄ was revealed by In situ XPS,DFT,and so on,which was responsible for enhanced photocatalytic activity of TiO₂@CaIn₂S₄ nanofibers.2.Cu₃（BTC）₂ was first hydrothermally prepared by using Cu（NO₃）₂·3H₂O and1,3,5-benzenetricarboxylic acid as precursors.Then,the Cu₃（BTC）₂@TiO₂ core-shell heterojunction photocatalysts were constructed by the deposition of TiO₂on the surface of Cu₃（BTC）₂ using butyl titanate as the titanium source via a hydrothermal method.The experimental results indicated that the Cu₃（BTC）₂@TiO₂ photocatalyst with reversible self-healing ability exhibited significantly higher photocatalytic hydrogen production performance,which is about 72.2 times as high as that of pure TiO₂.The Cu₃（BTC）₂@TiO₂ heterojunction photocatalyst was further characterized by XPS and XRD,and so on,and a possible mechanism for enhancing the photocatalytic hydrogen production of the composite Cu₃（BTC）₂@TiO₂ was proposed.3.The macroporous/mesoporous TiO₂ was first prepared by hydrolysis of butyl titanate followed by high-temperature calcination.Next,the macroporous/mesoporous TiO₂@CaIn₂S₄ S-scheme heterojunction photocatalysts were hydrothermally prepared using CH₃CSNH₂as the sulfur source,In（NO₃）₃·4.5H₂O as the indium source,and Ca（NO₃）₂·4H₂O as the calcium source,respectively.The experimental results showed that the macroporous/mesoporous TiO₂@CaIn₂S₄ heterojunction photocatalyst possessed an enhanced photocatalytic CO₂ reduction performance,which was 5 times higher than that of pure TiO₂.The enhanced photocatalytic performance of macroporous/mesoporous TiO₂@CaIn₂S₄ was ascribed to the stronger redox ability of the S-scheme heterojunction at the interface between TiO₂ and CaIn₂S₄.Meantime,the macroporous/mesoporous structure is more favorable for the adsorption of CO₂,resulting in the easier photocatalytic reduction of CO₂.The physicochemical properties of the macroporous/mesoporous TiO₂@CaIn₂S₄ heterojunction photocatalyst were characterized using XPS,XRD,and so on.The pathway of photocatalytic CO₂reduction of macroporous/mesoporous TiO₂@CaIn₂S₄ heterojunction was further studied.The mechanism for the enhanced photocatalytic CO₂ reduction of TiO₂@CaIn₂S₄ heterojunction was proposed.