The Construction Of Oxygen-enriched Vacancy TiO_2-x Hierarchical Micro-nanospheres Loaded By Ni,MoS₂ And Their Photocatalytic Hydrogen Evolution Performance

TiO₂ nanomaterials have excellent chemical stability and high reactivity,and become the star material for water splitting catalysts.TiO₂ hierarchical micro-nanospheres（THS）are constructed of ultrathin nanosheets with extremely large specific surface area,which are helpful for the modification of cocatalyst loading and have attracted extensive attention.However,the band gap of 3.2 e V and the high recombination rate of photogenerated carriers restrict its development and application.The introduction of oxygen vacancies on the surface plays an important role in improving the light absorption capacity of TiO₂ and inhibiting photogenerated charge recombination.In this paper,hydrochloric acid and urea were mixed with THS,followed by annealing in air to introduce doping nitrogen and induce the formation of oxygen-rich defective TiO₂ hierarchical micro-nanospheres（THS（Ov））.Further cocatalysts such as Pt,Ni,and Mo S₂ are supported on the surface to improve the visible light absorption and photogenerated carrier separation ability of TiO₂,which is helpful to achieve efficient photocatalytic water splitting for hydrogen production.The main work includes the following three parts:（1）Pt-THS（Ov）（X）was successfully prepared by loading Pt co-catalyst on THS（Ov）by photoreduction method.The Pt co-catalyst was supported in the form of metal Pt,which did not change the morphology and structure of the original support.Compared with untreated Pt-THS（X）,the photocatalytic ability of oxygen vacancy-modified Pt-THS（Ov）（X）to split water for hydrogen evolution is significantly improved.Under full-spectrum（UV-Vis）irradiation,the photocatalytic performance of Pt-THS（Ov）（0.1wt%）for water splitting and hydrogen evolution reaches 4.55 mmol·g^-1·h^-1.The Pt co-catalyst,THS and oxygen vacancies exhibited a good synergistic effect.The oxygen vacancies repaired the band gap of the THS support well and provided anchor sites for the loading of the Pt co-catalyst.The surface plasmon resonance effect induced by the Pt cocatalyst further excites the transfer of electrons from the conduction band and oxygen vacancy energy levels to the Pt cocatalyst,and the Schottky junction formed on the surface of THS prevents the reverse transfer of electrons,the recombination of photogenerated electron-hole pairs is inhibited,which contributes to the improvement of the photocatalytic water splitting performance for hydrogen production.（2）The Ni-THS（Ov）（X）was successfully prepared by loading a non-precious metal Ni-based co-catalyst on THS（Ov）by impregnation photoreduction method.Ni-based co-catalysts are supported on the surface of THS（Ov）in the form of metallic Ni and Ni（OH）₂,which did not change the morphology and structure of the original support.Compared with untreated Ni-THS（X）,the photocatalytic ability of oxygen vacancy-modified Ni-THS（Ov）（X）to split water for hydrogen evolution is also significantly improved.Under full-spectrum（UV-Vis）irradiation,the photocatalytic performance of Ni-THS（Ov）（0.1wt%）for decomposing water for hydrogen evolution reaches 4.88 mmol·g^-1·h^-1.The formed Ni²⁺/Ni⁰ energy level is slightly lower than the CB of THS,and metallic Ni can act as a good co-catalyst to promote the transfer of photogenerated electrons of THS（Ov）to Ni species,and the reduction reaction occurs to generate H₂.The synergistic relationship among Ni-based co-catalysts,THS,and oxygen vacancies is further investigated,and Ni species can act as electron traps to capture electrons at the conduction band and oxygen vacancy levels.Due to the SPR absorption of Ni species in the visible light region,energy can be fed back to THS（Ov）,which is beneficial to the separation and transport of carriers in THS,and the formed Schottky junction has the effect of inhibiting the recombination of photogenerated electron-hole pairs.（3）MoS₂/THS（Ov）（X）was successfully prepared by loading Mo S₂ co-catalyst on THS（Ov）by hydrothermal composite method.The loading of Mo S₂ co-catalyst makes Mo S₂with flocculent morphology appear on the original hierarchical micro-nanospheres,and the XRD shows that the structure of the composite catalyst is the combination of anatase TiO₂ and amorphous Mo S₂.Under full-spectrum（UV-Vis）irradiation,Mo S₂/THS（Ov）（0.6:1）exhibited the best hydrogen evolution performance at 747.29μmol/g/h.Compared with the Mo S₂/THS（X）sample without oxygen vacancy treatment,the photocatalytic water splitting performance for hydrogen evolution is also improved.The improved catalyst performance is attributed to the synergistic effect between THS,oxygen vacancies and Mo S₂ co-catalyst.Oxygen vacancies and Mo S₂ enhanced the visible light absorption of THS at 400-800 nm and suppressed the recombination of photogenerated electron-hole pairs,while Mo S₂ provided more reactive sites for carriers and accelerated the electron transport rate.