Preparation Of TiO₂-Based Composite Photocatalysts With High Hydrogen Evolution Activity And Their Photocatalytic Performance

Energy is the basis of human survival and development,and the guarantee of sustainable development of economy and society.Among the various types of sustainable energy,solar energy is considered to be promising because of its abundance,economy,high capacity and environmental friendliness.However,natural solar radiation is scattered,intermittent and fluctuates constantly.Therefore,it is still a huge challenge to effectively utilize solar energy in a clean,economical and convenient way.Hydrogen is the cleanest and most promising energy carrier and can be converted into chemical energy through solar energy.Using semiconductor photocatalytic water splitting to produce hydrogen is an economic and clean technology,which is widely considered as one of the promising methods to deal with energy shortage and environmental pollution.TiO₂ photocatalytic materials are widely used in the field of photocatalysis due to their low price,non-toxicity and stable performance.However,the solar-hydrogen energy conversion efficiency of semiconductor TiO₂photocatalytic water splitting technology is still relatively low due to the low light absorption capacity,the easy recombination of photogenerated carriers and the high hydrogen evolution overpotential,which is difficult to meet the needs of practical applications.In this paper,aiming at reducing the wide optical bandgap and carrier recombination of TiO₂,TiO₂ nanocomposites with high hydrogen evolution activity are constructed by composite modification to broaden the light absorption range of TiO₂ and inhibit the recombination of photogenerated carriers,thus improving its photocatalytic hydrogen production performance.The morphology and microstructure of the samples were studied by polycrystalline X-ray powder diffractometer,scanning electron microscope,transmission electron microscope and automatic specific surface area and porosity analyzer;the chemical composition of substances was analyzed by Raman spectrometer,Fourier transform infrared spectrometer and X-ray photoelectron spectrometer;light absorption,charge separation and migration were studied by UV-Vis-NIR spectrometer,fluorescence spectrophotometer and photoelectrochemical measurement.The active species in the photocatalytic reaction system were studied by electron paramagnetic resonance spectroscopy;the photocatalytic hydrogen evolution activity was tested under simulated sunlight of 300 W xenon lamp,the photocatalytic activity evaluation system evaluated the photocatalytic performance and stability of the prepared photocatalysts.The change of band structure of TiO₂ and the mechanism of photocatalytic water splitting to produce hydrogen after composite modification were also discussed.The main research contents and conclusions are as follows:（1）N-type H₂O₂/C₆₀-TiO₂ composite photocatalyst with good hydrogen production performance was prepared by simple hydrothermal method.The results show that H₂O₂ promotes the formation of microsphere catalyst,and the composite has good dispersion and inhibits the increase of TiO₂ particle size under the action of C₆₀.The photocatalytic hydrogen evolution activity test showed that when loaded with Pt,all H₂O₂/C₆₀-TiO₂ composites with different C₆₀ contents showed higher photocatalytic activity than TiO₂:when the mass ratio of C₆₀ to TiO₂ was 1%,the composite photocatalyst had the best hydrogen evolution activity,41.6 mmol·g^-1h^-1,9.7 times of pure TiO₂.The research shows that the addition of functionalized fullerene broadens the light response range of TiO₂ and increases the photogenerated carriers’separation ability,thus improving its photocatalytic performance.In addition,the hydrogen evolution activity of the photocatalyst had not significantly decreased after 20 h cycle test,showing good stability.（2）Direct Z-scheme Bi₂WO₆/TiO₂ heterojunction photocatalyst was prepared by one-step solvothermal method.The analysis results show that the mixed solution of ethanol and acetic acid as solvent can improve the dispersion of the composite material,and the direct Z-scheme photocatalyst is only composed of two semiconductors in direct contact,which has a certain impact on the morphology and crystallinity of Bi₂WO₆/TiO₂,and the BET specific surface area of the composite is more than twice that of Bi₂WO₆/TiO₂ prepared by traditional hydrothermal method.The photocatalytic hydrogen evolution activity test showed that Bi₂WO₆ did not produce H₂,and the H₂-production rate of TiO₂ was only 0.1 mmol·g^-1h^-1;all Bi₂WO₆/TiO₂ heterojunction photocatalysts show higher photocatalytic activity than TiO₂:when the mass ratio of Bi₂WO₆ to TiO₂ is 6%,the composite photocatalyst had the best hydrogen evolution activity,which was 12.9 mmol·g^-1h^-1,129 times that of TiO₂.The research shows that the enhancement of hydrogen evolution activity of heterojunction catalyst is mainly due to the wider light absorption range after TiO₂ is in close contact with Bi₂WO₆,which realizes the effective separation and migration of carriers,and shows high photocatalytic hydrogen evolution activity and durability.