Study On Preparation Of TiO₂ Nanocomposite And Its Hydrogen Production Performance

The global economic is developing and the population is soaring,the energy and environmental problems are increasingly prominent.So that the development of sustainable renewable energy has become one of the primary tasks for human survival and development.As a clean secondary energy source,hydrogen energy has some advantages,such as,large energy density,high combustion calorific value and rich sources.It is also storable,combustible,zero-pollution and zero-carbon emission.Hydrogen energy is helpful to solve the problems of energy crisis and environmental pollution,and it is considered as the"Ultimate Energy"in the 21st century.Photocatalytic hydrogen production from water splitting using solar energy is a potential,environmental and sustainable way for producing hydrogen energy.The efficiential photocatalyst is the key to the application of photocatalysis technology.TiO₂ is one of the most widely used photocatalyst in the field of photocatalysis due to its suitable energy band location,non-toxicity,strong photochemical stability,environmental friendliness,low cost and easy availability.However,it also has the disadvantage of large bandgap width（3.2 eV）and high recombination rate of photogenerated carriers,which greatly limit the photocatalytic activity.In respect of the issues above in this paper,we use TiO₂ as the support to load sulfide（narrow band gap semiconductor）and graphene quantum dots form a ternary composite photocatalyst system.High hydrogen production and photodegradation performance are caused by sulfide’s narrow band gap,which can enhance the visible light absorption and promote the separation of photogenerated carriers and the transfer of interfacial photogenerated charge on the heterojunctions.The main research content as follows:（1）TiO₂ was prepared by hydrothermal method.We investigated the influence of titanium source and hydrothermal reaction temperature on the morphology of TiO₂.The results shows that the morphology and structure of TiO₂ nanomaterials were greatly affected by the hydrothermal temperature.When hydrothermal reaction temperature is 200°C,TiO₂nanosheet were synthesized while titanate nanotube（TNTs）were synthesized when it is130°C.Under ultraviolet light,the catalytic degradation rate of methyl orange is TNTs（commercial）>TNTs（TiCl₄）>TNTs（TBOT）,indicating that the nanotube synthesized from commercial TiO₂ powder has the highest degradation activity of methyl orange.The results of hydrogen production under simulated solar irradiation shows that the TiO₂ nanosheet were only 111.6μmol/g higher than TiO₂ nanotubes.（2）A ternary CdS-GQDs-TNTs nanocomposite catalyst was prepared by in-situ method.At first,the graphene quantum dots（GQDs）were loaded on titanate nanotubes（TNTs）by solvent heat method.And then the CdS QDs were loaded on TNTs by ion exchange followed by sulfurization method.The hydrogen production performance shows that the ternary CdS-GQDs-TNTs nanocomposite exhibit better photocatalytic hydrogen rate than binary CdS-TNTs and GQDs-TNTs composite.The photocatalytic mechanism was studied by electrochemical technology,and the results shows that the synergistic effect of quantum dots and CdS promoted the effective separation of photogenerated carriers,improved the absorption of visible light,prolong lifetime of photogenerated carriers,and promote the interfacial charge transfer.Under simulated sunlight,the ternary CdS-GQDs-TNTs nanocomposite catalyst produced 2678μmol/g more than pure TNTs.（3）Mixed phase 1T/2H MoS₂ was prepared by simple hydrothermal method and investigated the photocatalytic hydrogen production performance of 1T/2H MoS₂-TiO₂photocatalyst.Due to the wide optical absorption range of 1T/2H MoS₂ and more hydrogen reduction active sites,the hydrogen yield of MoS₂-TiO₂ for 8 h up to 2976.2μmol/g under simulated sunlight.（4）In this study,NiS/TiO₂ was synthesized by Successive ionic layer adsorption and reaction（SILAR）method using nickel nitrate as cationic source and sodium sulfide as anion source.Compared photocatalytic hydrogen production performance of samples prepared by using different Ni precursor with different concentrations.The results shows that the highest hydrogen production is NiS/TiO₂ prepared by Ni precursor concentration of 0.04mol/L,which is up to 2366.07μmol/g.