Preparation Of TiO₂-Based Photocatalyst And Its Catalytic Rule For Hydrogen Production From Biological Methanol

Biomass energy is rich in reserves and effective utilization of biomass resources is the focus of current research.Photocatalytic reforming of biomass to produce hydrogen is a mild biomass utilization technology.Methanol is used as a model compound of biomass derivatives in photocatalytic process,and its function is to as a hole scavenger and hydrogen donor.The core of photocatalytic reaction is to find efficient and stable photocatalyst.TiO₂ is a kind of photocatalyst with excellent performance,which is widely used in the field of reforming biomass to produce hydrogen.However,the performance of TiO₂ is restricted by the fast electron-hole recombination and the wide band gap.The hydrogen production activity of TiO₂ can be further improved by means of constructing heterojunction,doping nonmetallic elements,loading noble metals,and adjusting morphology.We have conducted the following research:（1）A novel g-C₃N₄/TiO₂/CuO double heterojunction photocatalyst was developed to test its photocatalytic activity for hydrogen production in water-methanol solution.Due to the close interface contact established by the double heterostructure,the g-C₃N₄/TiO₂/CuO catalyst had the best hydrogen evolution rate of 97.48μmol/（g·h）under visible light irradiation.Compared with g-C₃N₄/TiO₂ and CuO/TiO₂,the photocatalytic hydrogen production activity of g-C₃N₄/TiO₂/CuO was increased by about 7.6 times and 1.8 times respectively.The band gap width of g-C₃N₄/TiO₂/CuO double heterojunction photocatalyst was 1.38 e V through UV-vis characterization.PL and transient photocurrent characterization showed that the double heterojunction could control the recombination of electron hole pairs and enhanced the migration of photogenerated electrons.The movement of photogenerated electrons in the double heterojunction was explained through the S-scheme mechanism.（2）The band gap width of TiO₂ was controlled by doping nonmetallic element N.The content of introduced N element was controlled by different ammonia annealing temperatures of TiO₂.The introduction of N element can induce the impurity band gap below the conduction band of TiO₂.In addition,N element adjusts the valence state of adjacent Ti element and leads to the generation of oxygen vacancies.According to the results of photocatalytic hydrogen production,300-N-T catalyst had the best photocatalytic hydrogen production performance under visible light,up to 307.65μmol/（g·h）.XPS and EPR characterization showed that the concentration of Ti³⁺defects and oxygen vacancies in N-TiO₂ increased with the increase of N content.According to UV-vis characterization,the band gap of 300-N-T photocatalyst could be reduced to 2.73 e V,confirming that there were impurity energy levels near conduction band and valence band of TiO₂ materials.Instantaneous photocurrent response and EIS characteristics confirmed that Ti³⁺ion was the active site of photocatalytic reaction.（3）The hollow TiO₂ catalyst was prepared by the sol gel template method,and Pt and N were introduced into TiO₂ by ammonia calcination and photoreduction methods.In order to explore the synergetic regulation of Pt and N elements,the performance of TiO₂（HS）-N-xwt%Pt in hydrogen production by biomass oxidation under visible light was tested.In this experiment,when the loading amount of Pt was 1wt%,the photocatalytic hydrogen production performance reached the maximum of 3113.63μmol/（g·h）.The Ti³⁺and oxygen vacancy contents of TiO₂（HS）-N-1wt%Pt were 77.91%and 7.391（×）10¹⁶spins/g,respectively by EPR and XPS characterization.The introduction of Pt could further increase the content of Ti³⁺and oxygen vacancy in TiO₂.UV-vis characterization confirmed that Ti³⁺and oxygen vacancy successfully introduced impurity band gap into TiO₂ band gap,effectively reducing its band gap width to 2.28 e V.