Preparation Of TiO₂ Nanocomposite Structures And Study On Photoelectric Catalysis Performance

Highly ordered TiO₂ nanotube arrays（TNTAs）fabricated by electrochemical anodic oxidation method have broad applications in the fields of photoelectrochemical（PEC）water splitting,supercapacitors and solar cells because of their large specific surface area and stable structure.However,TiO₂ itself has a wide band gap,low utilization rate of sunlight and poor electrical conductivity,which limits its practical application. Modification or combination with other materials can significantly improve the PEC and electrochemical performances of TNTAs.In this paper,highly ordered TNTAs were fabricated by electrochemical anodic oxidation,and modified by MnO₂ in a chemical bath deposition process.In addition,graphene quantum dots were further modified by electrophoresis to improve the PEC and electrocatalytic properties of the TNTAs.The relationship of annealing temperature,chemical bath deposition temperature and growing time with TNTAs phase structure and PEC performance were investigated systematically.The main research results are as follows:（1）The PEC water splitting performance of TNTAs was tuned by adjusting the annealing temperature to control the phase structure and compositon.Characterization and performance analysis show that,TNTAs was anatase phase and the morphology of the nanotube structure kept unchanged at the annealing temperature between 300-500℃,while the temperature increase to 600℃and 700℃,the anatase phase began to change into rutile phase,and the mouth and wall of the nanotube showd different degrees of rupture.The PEC performance test shows that the TNTAs exhibited the best photoconversion efficiency of up to 0.58%under 400℃annealing temperature.（2）MnO₂@TNTAs composite arrays were prepared in a chemical bath deposition process with different and MnO₂morphologies which was controlled by adjusting the deposition temperature.The MnO₂ nanowires@TNTAs（MNW@TNTAs）were be obtained under 85℃,and it is the first time of reporting this kind of composite structure.Optical absorption measurement suggests that the bandgap width of the hybrids can be tuned from 3.2e V of TNTAs to 2.18e V of the MNW@TNTAs hybrid arrays,and the optical response current of TNTAs can be improved in visible region.The internal resistance of TNTAs was also effectively reduced and the PEC efficiency was improved as well.The H₂ generation rate of the MNW@TNTAs hybrid arrays in 5 hours can achieve 20.8μmol·h^-1cm^-2,which is twice times as the TNAs.（3）TNTAs modified by graphene quantum dots（GQDs/TNTAs）was prepared by electrophoresis.The comparative analysis of the performance shows that the internal resistance of TNTAs modified by GQDs decreased obviously,which suggests that the GODs improved the electrical conductivity of the TNTAs,and the electrode obtained under 6V voltage showed a minimum resistance of only 87.66Ω.Thus,GQDs/TNTAs obtained under 6V electrophoresis voltage was selected as the base,and the compound growth of MnO₂ with GQDs/TNTAs was achieved by chemical bath （MnO₂@TNTAs/GQDs）.The load of the MnO₂ was regulated by adjusting the deposition time of the chemical bath.PEC performance test shows that the synergistic effect between GQDs and MnO₂ further reduce the internal resistance of the TNTAs,which improved the catalytic performance of the composite samples.Moreover,the band gap of TNTAs was also tuned which significantly improved the response of the composite structure to visible region.The optimized composite electrode showed a maximum limiting current of-26.97 m A/cm²,and the hydrogen generation rate was about 37.5μmol·h^-1cm^-2,which was nearly 4 times higher than that of the TNTAs.