Synthesis Of One-dimensional Mesoporous Ti O₂ Modified With Nickel-based Cocatalyst And Insights Into Their Enhanced Photocatalytic Hydrogen Evolution Performance

Solar energy induced photocatalytic water splitting to hydrogen has been attacted great intention in recent years.One dimensional mesoporous TiO₂ has been considered as one of the most promising meaterials for photocatalytic hydrogen evolution because of its unique morphology and large surface area.Up to now,the fast recombination rate of photoinduced electrons-hole pairs in pure TiO₂ has limited its hydrogen evolution performance.Fortunately,the involving of cocatalyst into semiconductor-based photocatalysis system can accelerate the separation of photoinduced electrons and holes and accordingly to improve photocatalytic hydrogen production performance.The cocatalyst can be divided into noble metal cocatalyst and noble-metal-free cocatalyst.Considering the high cost of noble metal,to find an efficient and low cost noble-metal-free cocatalyst has been received much attention.Among the various cocatalysts,nickel based materials with superior cocatalytic performance and suitable binding energy with hydrogen have been used as cocatalyst in photocatalytic water splitting to hydrogen.Based on the above background,the semiconductor-cocatalyst system has been constructured using one dimensional mesopoous TiO₂ host photocatalyst decorated with suitable nickel based nanoparticles in this thesis.The photocatalytic hydrogen evolution performance over TiO₂-nickel-based hybrids have been carried out,and the experimental condition and parameters have been optimized.The charge separation and migration on the surface of hybrids have been discussed.And the enhanced photocatalytic mechanisms have also been illuminated.The main works are summarized as follows:1.A highly efficient photocatalytic hybrids of TiO₂-Ni（HCO₃）₂ were successfully fabricated by a hydrothermal approach using titanium glycolate,Ni（NO₃）₂,and urea as the precursor.The morphology,structure and composition of hybrids had been characterized by X-ray powder diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscope（SEM）,and transmission electron microscopy（TEM）.According to the photocatalytic hydrogen evolution experiments results,the involvement of Ni（HCO₃）₂ cocatalyst resulted in significant improvement of the hydrogen evolution on the host TiO₂ photocatalyst under artificial sunlight irradiation.The optimized hybrid photocatalysis system with 2.5%（mole ratio）Ni（HCO₃）₂ loading displayed the highest hydrogen evolution rate of 1798.0 μmol g^-1 h^-1,which was more than 18 times higher than that of pure mesoporous TiO₂.On the basis of the photoluminescence spectroscopy and time-resolved photoluminescence,and photoelectrochemical measurements results,it is proposed that the enhancement of photocatalytic hydrogen evolution capability on the TiO₂-Ni（HCO₃）₂ host photocatalystcocatalyst is not only attributed to the efficient separation of photo-induced electron-hole pairs,but also derived from the Ni（HCO₃）₂ cocatalyst being acted as active reaction sites towards hydrogen production.2.The photocatalytic hybrids of NiS/Ni₃S₄ cocatalysts modified mesoporous TiO₂ had been successfully fabricated by hydrothermal method using titanium glycolate,Ni（NO₃）₂,and thiourea as the precursor.The morphology,structure and composition of hybrids had been characterized by XRD,XPS,SEM,and TEM.The impacts of content of Ni Sx and different hole scavengers over photocatalytic hydrogen evolution on hydrids had been studied.When using methanol as hole scavengers,the hybrid of TiO₂ decorated 3% mole ratio Ni Sx cocatalyst achieved the optimal photocatalytic hydrogen evolution rate of 981.59 μmol h^-1 g^-1,which was about 20 times higher than that of bare mesoporous TiO₂.Based on the photoluminescence and time-resolved photoluminescence spectroscopy,and photoelectrochemical measurements results,it was found that the boosted hydrogen production performance is attributed to the synergistic impacts of improved photoinduced electrons by Ni Sx cocatalyst and the high hole captured efficiency by hole scavengers of methanol.3.Mesoporous TiO₂ decorated with Ni nanoparticles was successfully prepared by facile hydrothermal method using titanium glycolate,Ni（NO₃）₂,and hydrazine as the precursor.And the corresponding morphology,structure,and component were characterized by XRD,XPS,SEM,and TEM.The experimental results revealed that Ni cocatalyst could greatly improve the photocatalytic hydrogen evolution performance,and the hybrid with mole ratio 1% Ni cocatalyst showed the highest hydrogen evolution performance.Moreover,the hydrogen evolution over TiO₂-Ni-1% had been carried out using paper as hole scavenger in different concentration Na OH solution.The results indicated that the optimal hydrogen evolution rate of 253.28 μmol h^-1 g^-1 with the Na OH concentration of 0.5 mol/L.On the basis of photoluminescence and time-resolved photoluminescence,photoelectrochemical measurements,and hydroxyl radical trap experiment results,the Ni nanoparticles as cocatalyst could effectively accelerate photo-induced electrons migration,improving the hydrogen reduction process.And soluble paper in alkaline solution would react with strong oxidizing hydroxyl radical formed by hole oxidation with OH-,exhibiting the sacrificial electron donors capability.The processes of hydrogen reduction and hole oxidation would achieve the photocatalytic water splitting to hydrogen.