Study On The Photoelectrochemical Properities Based On The Doped TiO₂ Nanomaterials

In the 21 century,with the rapid growth of population and the rapid development of social industrialization,the sustainable development of resources,environment,population and human society has become an urgent problem to be solved.Energy conservation and environmental protection become the core problem of ecological protection,In many energy development and environmental protection and efficient new energy improvement strategies,photocatalysis with semiconductor oxide as catalyst is a kind of green environmental protection technology,which is characterized by: mild reaction conditions and application Wide range of direct use of sunlight as a light source to activate the catalyst and drive the redox reaction and other unique properties,its research has aroused widespread concern.Titanium dioxide?TiO₂?is not only a transition metal oxide but also a semiconductor material,because of its good chemical stability,good photocatalytic capacity,non-toxic,cheap and other properties,which have great potential applications in the solar cells,biomedical,sewage treatment,air purificationand and other fields.However,the band gap of TiO₂ is large?Eg =3.0 e V-3.2 e V?,which limits its visible light absorption capacity.TiO₂ can only be the wavelength of less than 387 nm ultraviolet excitation to play a catalytic role,and these light only 4% of the whole sunlight the sun,the utilization of sunlight is very low.In addition,the photogenerated electrons and hole pairs generated by pritine TiO₂ are easily recombined,which leads to low photocatalytic quantum efficiency.These two aspects of the shortcomings to a large extent limit the widely use of nano-TiO₂.The results show that changing the morphology of TiO₂ and modifying TiO₂ which can solve the above two problems.Compared with TiO₂ nanoparticles,TiO₂ nanotubes have greater specific surface area,stronger adsorption capacity and higher photocatalytic activity.In order to achieve the catalytic application under natural light conditions,the researchers used a variety of methods to modify nano TiO₂,such as precious metal deposition,metal ion doping,non-metallic doping,semiconductor recombination,photo-sensitization.In order to overcome the above shortcomings of TiO₂,the aim of this study is to prepare doped TiO₂ nanotube photocatalytic materials with high catalytic activity in the ultraviolet and visible regions.In this paper,a highly ordered array of TiO₂ NTs was prepared by anodic oxidation method using titanium as the substrate.The photoelectrochemical properties of Ti3+ doped TiO₂?B?NSs-TiO₂ NTs,P5+doped TiO₂ NTs and P5+ and Cr3+ co-doped Sr TiO₃-TiO₂ NTs nanocomposites were investigated.The morphology,structure,optical properties and photoelectrochemical properties of TiO₂ nanotubes before and after doping were studied by SEM,TEM,XRD,UV-vis,XPS,UPS,LSV,VOC,IMPS and so on.The main results of this paper are as follows:?1?Preparation of Ti3+-TiO₂?B?NSs/TiO₂ NTs films: First of all,the H2Ti3O7 nanosheet films were prepared on Ti foil by hydrothermal method,and then TiO₂?B?NSs/TiO₂ NTs were obtained by ion exchange after annealing and anodic oxidation of the H2Ti3O7 nanosheet.Na BH4 as the reducing agent,N2 as the protective gas and annealed at 400? for 2 h to obtain Ti3+-TiO₂?B?NSs/TiO₂ NTs film.The SEM and XRD results show that in the Ti3+-TiO₂?B?NSs /TiO₂ NTs films TiO₂?B?NSs are grown on the top of TiO₂ NTs.The thickness of TiO₂?B?NSs is about 30 nm and the length of TiO₂ NTs is about 3.5 ?m.The Photonic current density of Ti3+-TiO₂?B?NSs/TiO₂ NTs films is 0.34 m A·cm-2?1.23 V vs RHE?,and the photoelectrochemical properties are obviously improved.?2?Preparation of P-TiO₂ NTs films: Anodic oxidation method was used to prepare highly ordered TiO₂ NTs arrays with different oxidation times.Sodium hypophosphite as a phosphorus source,N2 as protective gas.P-TiO₂ NTs were prepared by low temperature calcination.The effects of different concentrations of PH3 on the photocatalytic activity of P-TiO₂ NTs were investigated.The results show that P doping has no obvious effect on the morphology and structure of TiO₂ NTs.Compared with pristine TiO₂ NTs,the absorption intensity of doped TiO₂ is improved obviously.The experimental results show that the photocurrent density of anodic oxidation of 7 h TiO₂ NTs film annealing in air at 500? was 1.0 m A·cm-2?1.23 V vs RHE?,and its photocurrent density can reach 2.5 m A·cm-2 after doping?1.23 V vs RHE?.?3?Preparation of P-Cr-Sr TiO₃/TiO₂ NTs heterojunctions: Sr TiO₃/TiO₂ NTs heterojunctions were successfully prepared by hydrothermal method and anodic oxidation method using Ti foil as substrate.Cr?NO3?3·9H2O as Cr3+ dopant,in situ heat treatment of Cr3+ in situ doping.The experimental results show that P and Cr co-doping has no obvious effect on the heterojunction morphology of Sr TiO₃/TiO₂ NTs,and the photoelectrochemical properties can be improved obviously.On the one hand,P and Cr co-doped can form impurity energy level and reduce Sr TiO₃/TiO₂ NTs heterojunction band gap;on the other hand,it is possible to suppress the recombination of Cr3+ by in situ doping.The photocurrent density of P-Cr-Sr TiO₃/TiO₂ NTs was 2.0 m A·cm-2 under the condition of AM 1.5 G and light intensity of 100 m W/cm2?1.23 V vs RHE?.