Study On Mechanism Of Enhanced Photocatalytic Hydrogen Production Activity Of Nickel-based Cocatalyst Modified Titanium Dioxide

Titanium dioxide（TiO2）with suitable valence band and conduction band has been widely used in photocatalytic hydrogen production due to its potential in oxidation and reduction of water upon light irradiation.In addition,owing to its stable chemical properties,photo-corrosion resistance,and non-biotoxicity,TiO2 has became the most promising and well studied photocatalyst in the field of photocatalytic water splitting.However,its slow migration speed and high recombination rate of photogenerated electron-hole pairs resulted in the low photocatalytic quantum efficiency and photocatalytic activity,which limited its further development in the photocatalysis.Numerous studies demonstrated that the introduction of noble metal cocatalyst could effectively improve the photocatalytic hydrogen production performance of photocatalysts.Nevertheless,the scarcity and expensive price of precious metals restricted its practical application in photocatalytic hydrogen production.As an earth-rich,widely available and inexpensive element,nickel could be an effective active site in the hydrogen adsorption process,and also possess a suitable Ni-H adsorption energy.Nickel-based materials has been widely used as an electrocatalyst and the cocatalyst of photocatalysts for hydrogen production.Therefore,nickel-based materials are the most promising materials to replace precious metals.In this thesis,nickel-based cocatalyst was introduced on the surface of P25,and the photocatalytic hydrogen production activity of the composited material was investigated.Furthermore,the composition,structure,photoelectric performance and catalytic performance of the nickel-modified P25 was analyzed to further understand the mechanism of enhanced photocatalytic activity of the composited materials.The main content of the thesis is summarized as follows:1.Ni6（SCH2Ph）12 crystals were synthesized with nickel chloride and benzyl mercaptan as raw materials,and tetra-n-octylammonium bromide（TOAB）as solubilizer by ion exchange and coordination reactions.Nickel-containing complex Ni6（SCH2Ph）12modified P25 material was obtained by simple rotary evaporation.It showed that the photocatalytic hydrogen production activity of the modified sample was significantly improved.The photocatalytic hydrogen production activity of the composited material was further optimized by changing the type of sacrificial agent and the amount of photocatalyst.The optimal modification amount of the nickel-containing complex Ni6（SCH2Ph）12 was determined to be 5 wt%.Under the optimized conditions,the photocatalytic hydrogen production rate of the Ni6/P25 sample was 5632μmol g^-1 h^-1,which was about 29 times as much as that of P25 material under the same conditions.The photoelectric test results showed that the introduction of Ni6（SCH2Ph）12 could effectively improve the shortcomings of slow carrier separation and migration rate and high photogenerated electron-hole recombination rate.The photocatalytic activity comparison of the 5.0-NP sample before and after calcination indicated that the presence of ligands was beneficial for the photocatalytic reaction because the ligands could facilitate the dispersion of active sites and avoide the formation of recombination centers.Moreover,the presence of heterojunction between these two types of titanium dioxide in P25 might promote charge transfer between them.2.NiB and NiB/P25 catalyst was prepared by a simple one-step reduction method.Powder X-ray diffraction results showed that NiB was non-crystalline and amorphous.By adjusting the amount of nickel source and boron source,NiB modified P25 materials with different proportions were obtained.It was found that the introduction of NiB significantly improved the photocatalytic activity of the P25 material.The photocatalytic hydrogen production rate of the optimized NB-3 sample was 2651.6μmol g^-1 h^-1,which was about 110 times as much as that of P25 under the same conditions.The decrease in the activity of the calcined material indicated that the amorphous NiB was more conducive to photocatalytic hydrogen production than NiB with high crystallinity.Photoelectric tests showed that the introduction of NiB reduced the overpotential for hydrogen production,promoted the separation and migration of photogenerated electrons and holes in the material,and increased the density of electrons.The 24-hour continuous hydrogen production test showed that the composited material NiB/P25 possessed a good stability.