Study On Hydrogen Production By Photoelectrocatalytic Water Splitting And Photocatalytic Degradation Of Organic Pollutants Of Semiconductor/TiO₂ Nanotube Arrays

As an important inorganic semiconductor functional material,nanostructured titanium dioxide?TiO₂?has attracted considerable interest in photocatalytic field for its ehemical stability,thermal stability,nontoxicity and low cost,and has been widely used in solar cells,biomaterials,gas sensor and so on.Compared to TiO₂ nanoparticles,the highly ordered TiO₂ nanotube arrays possess good charge transfer and high specific surface area,and have exhibited excellent photoelectric conversion and photocatalytic performance.However,there are still two main factors which limit the further application of TiO₂ nanotube arrays.Firstly,the band gap of TiO₂ is larger?3.2 eV for anatase TiO₂ which only absorbs UV light with ?<387 nm?,and thus TiO₂ nanotube arrays can not absorb visible light which accounts for most energy in the solar spectrum.Secondly,the high photoinduced electron-hole recombination rate results in short photoinduced carriers' lifetime,as well as low photoelectric conversion efficiency and quantum efficiency.To this end,many researchers always explore various methods to increase the photocatalytic performance of TiO₂ nanotube arrays.In terms of the photocatalytic problems of TiO₂ nanotube arrays,this work is aimed at expanding the photoresponse range of TiO₂ nanotube arrays by semiconductor coupling,and repressing the photogenerated electron-hole recombination,improving the quntumn efficiency,consequently facilitating the application of TiO₂ nanotube arrays in visible light photoelectrocatalytic water splitting for hydrogen production and photocatalytic degradation of organic pollutants.The main progress and results are outlined as following:?1?CdS quantum dots/TiO₂ nanorods/TiO₂ nanotube array?CdS/TNRs/TNTs?composite electrode was prepared by a hydrothermal method to deposite the"flower-like”TiO₂ nanorods and a sequential-chemical bath deposition?S-CBD?method to deposite the CdS quanyum dots successively on TiO₂ nanotube arrays.The result of hydrogen production by photoeletrocatalytic water splitting indicats that CdS/TNRs/TNTs shows an intense absorption in the range from 400 to 700 nm and the photocurrent and hydrogen production rate of CdS/TNRs/TNTs under visible light irradiation are significantly increased.The hydrogen production rate of CdS/TNRs/TNTs increased approximately 13 and 2 times than that of the TNTs and the CdS/TNTs,respectively,which is attributed to the increased deposition amounts of CdS QDs due to "flower-like" rutile TiO₂ nanorods on TiO₂ nanotube arrays.In addition,CdS/TNRs/TNTs exhibit excellent hydrogen production stability using Na₂S and Na₂SO₃ as sacrificial reagents.?2?LaFeO₃ nanoparticles-modified TiO₂ nanotube arrays were synthesized through hydrothermal method.The results of diffuse reflectance spectroscopy?DRS?indicated that the absorption edge of LaFeO₃ nanoparticles-modified TiO₂ nanotube arrays appeared red shift to?540 nm due to modifying LaFeO₃ nanoparticles compared to TiO₂ nanotube arrays,indicating that the sample had the enhanced visible light response.The result of Photoluminescence?PL?showed that the LaFeO₃ nanoparticles modified on TiO₂ nanotube arrays inhibited the recombination of photoinduced electron-hole pairs and effectively prolonged the lifetime of photoinduced carriers.The degradation of MB solution under visible light irradiation displayed that the photocatalytic activity of LaFeO₃ nanoparticles-modified TiO₂ nanotube arrays is obviously increased.LaFeO₃ nanoparticles-modified TiO₂ nanotube arrays prepared by hydrothemal reaction for 10 h exhibited the highest degradation rate with a 2-fold enhancement compared with that of TiO₂ nanotube arrays.?3?The LaCoO₃ nanoparticles were prepared by using co-precipitation method and then were uniformly deposited on the TiO₂ nanotube arrays through ultrasound-assisted impregnating method.The results indicated that,the the absorption edge of LaCoO₃ nanoparticles-modified TiO₂ nanotube arrays was extended to 720 nm.The LaCoO₃ nanoparticles-modified TiO₂ nanotube arrays prepared by ultrasound-assisted impregnation for 2 h exhibited the highest visible light photocatalitic activity,and a 2-fold enhancement in degradation rate of MB was achieved compared with TiO₂ nanotube arrays.