The Preparation And Photocatalytic Water Splitting For Hydrogen Production Of NiO/Ni/TiO₂ And Ni?OH?₂/Pt/TiO₂ Nanocomposites

Nowadays,traditional fossil fuel resources are increasingly exhausted and the environmental problems caused by their burning also affect global climate change and endanger human's physical and mental health.The development and utilization of new energy sources and the resolution of serious energy,environmental issues are the focus of all countries in the world.In 1972,Honda and Fujishima reported the results of using titanium dioxide as an electrode to absorb ultraviolet light for photolysis of water.The use of semiconductor photocatalysts to convert light energy into usable hydrogen energy,providing an effective way to solve energy and environmental problems.Titanium dioxide is one of the most widely used semiconductor photocatalyst.However,its band gap is 3.2eV,which can be only activated by the near-ultraviolet region.Besides,the rapid recombination of photo-generated electron-hole pairs also diminishes the photocatalytic ability of TiO₂ and limits its application.The construction of heterojunction and metal Schottky junction can promote the separation efficiency of photogenerated carriers at the heterojunction interface and enhance the absorption of visible light and improve the photocatalyticperformance.Inthispaper,NiO/Ni/TiO₂andNi?OH?₂/Pt/TiO₂nanocomposites are prepared.Their composition,morphology and photoelectric properties are characterized by a series of tests like XRD?XPS?SEM?TEM?BET?PLand some other analysis methods.The properties of hydrogen production by photocatalytic water splitting under visible light are measured and studied.One-dimensional nanotube TiO₂ precursors are prepared by ultrasonic and hydrothermal method,then Ni/TiO₂ are synthesized by chemical reduction and NiO/Ni/TiO₂nanocomposites are prepared by simple oxidation.The characterization of the material's morphology by SEM and TEM indicate that the composites are uniformly attached to the surface of the TiO₂ nanotubes and maintain a one-dimensional structure.The addition of metal Ni into the p-n heterojunction NiO/TiO₂ forms a cooperative heterojunction of both p-n heterojunction and the Schottky junction.The metal Ni forms a Schottky junction with the semiconductor and it is also used as an electron transport channel embedded in the p-n heterojunction NiO/TiO₂,which effectively improves the photoelectron-hole separation rate;the carrier mobility is enhanced;the light absorption in the visible light region is obviously improved;the instantaneous photocurrent density is increased and the impedance value is decreased.In addition,the optimum amount of nickel is explored,the material exhibits the best performance in all aspects when the molar ratio of Ni to Ti is 8.17%.The hydrogen production rate of NiO/Ni/TiO₂ under visible light is up to 4653?mol·h^-1·g^-1,which is 10.1times of the original TiO₂(457?mol·h^-1·g^-1).After cyclic stability photocatalytic reaction,the photocatalytic activity is almost unchanged,indicating that the material has good stability.The one-dimensional original nanotubes TiO₂ are prepared by ultrasonic and hydrothermal method,and then Ni?OH?₂/Pt/TiO₂ nanocomposites are prepared by chemical reduction and precipitation in lye by using H₂PtCl₆·6H₂O and Ni?NO₃?₂·6H₂O as reactants.The Schottky junction and the semiconductor nickel hydroxide are used together to modify TiO₂,which form a multi-component heterojunction system.The results of light absorption,photoelectron-hole separation,photocurrent density,electrochemical impedance and band structure are analyzed.Ni?OH?₂/Pt/TiO₂ multi-component heterojunction material improves interface charge transfer;photogenerated electron-hole recombination decreases;instantaneous photocurrent density increases,impedance value decreases;the band gap is reduced,which could increase the application under visible light.The hydrogen production under visible light reaches 5875?mol·h^-1·g^-1,which is 43.8 times that of the original TiO₂nanotubes(134?mol·h^-1·g^-1),cyclic stability test results indicate that the material has good stability.