Study On The Modification Of Hydrogenated TiO₂ Nanotube Arrays And Their Photoelectrochemical Properties

At present,environmental problems,especially water environment problem,are becoming more and more serious,which arouse the concern of many people.In order to effectively control the environmental pollution of water bodies,it is necessary to monitor the water environment in real time.Therefore,an efficient,fast and environmentally friendly detection method is needed.Among them,TiO₂nanotubes have been widely used in photoelectrochemical detection due to the excellent photoelectrochemical performance,large specific surface area and good binding properties with substrates.However,the band gap of TiO₂is wide,and the photo-generated electron-hole pairs are easily recombinated,which limits its application in photoelectrochemical detection.In view of the above problems,TiO₂nanotube arrays were subjected to reduction treatment and phosphating treatment to improve their photoelectrochemical performance,respectively.Then Bi₂O₃was modified on the surface of nanotubes,and the photoelectrochemical detection performance was explored.The specific research work and comclutions are as follows:(1)TiO₂NTAs were prepared by two-step anodization method,and then thenanotubes were reduced by hydrogen thermal reduction and electrochemical reduction methods.The photoelectrochemical performances of TiO₂-H NTAs and TiO₂-E NTAs prepared with different reduction time were investigated.And the differences between the two reduction methods were studied and analyzed.Morphologies,structures,chemical compositions and photoelectrochemical performances of TiO₂NTAs,TiO₂-H NTAs and TiO₂-E NTAs were characterized by scanning electron microscope,X-ray diffraction diffractometer,X-ray photoelectron spectroscopy and electrochemical workstation.The results show that the photoelectrochemical performance of TiO₂-H4NTAs and TiO₂-E30 NTAs achieve the highest photocurrents of 250?A and 225?A respectively.The hydrothermal reduction treatment mainly occurs in the surface nozzle portion of TiO₂NTAs,which can increase the optical absorption intensity,reduce the oxygen evolution overpotential,promote the separation of electron-hole pairs.Therefore,the photoelectrochemical performances of TiO₂NTAs are improved,and the properties are relatively stable,which can be placed in the air for a long time without being oxidized.Electrochemical reduction mainly occurs in the bottom part of TiO₂nanotubes,which can make the TiO₂NTAs resistance change significantly with metal-like characteristics.Small charge carrier transfer resistance is the key factor to improve its photoelectrochemical performance.However,it is unstable and easily to be oxidized,which cannot be placed in the air for a long time.(2)TiO₂-H NTAs with the best photoelectrochemical performance were prepared by hydrogen thermal reduction.And Bi₂O₃/TiO₂-H NTAs were prepared using Bi₂O₃nanopaticles by ultrasonication-assisted successive ionic layer adsorption and reaction(SILAR)process.Morphologies,structures,compositions and photoelectrochemical performances of Bi₂O₃/TiO₂-H NTAs were characterized by scanning electron microscope,transmission electron microscope,X-ray diffraction diffractometer,X-ray photoelectron spectroscopy and electrochemical workstation.The results show that the hydrothermal reduction treatment can provide more active sites for TiO₂NTAs,which is beneficial to the deposition of Bi₂O₃nanoparticles,and improve the light absorption performance and energy level structure.Modification of Bi₂O₃nanoparticles can effectively inhibit the photolysis process of TiO₂-H NTAs,reduce the background photocurrent of TiO₂-H NTAs in the buffer solution,thereby reducing the current fluctuation during the detection of organic matter and improving the detection limit of the sensor.In addition,the modification of Bi₂O₃nanoparticles promotes the direct oxidation of organic matter by holes,which can improve the response photocurrent to organic matter of TiO₂-H NTAs,and improve the detection sensitivity of the sensor.The optimized Bi₂O₃/TiO₂-H NTAs sample possesses a sensitivity of 0.214?A/?M,a detection limit of 5.21?M,and a linear range of 0 to 1185.8?M.(3)Phosphating of TiO₂NTAs were prepared by thermal decomposition with Na₂HPO₂as phosphorus source.Then Bi₂O₃/TiO₂-P NTAs were prepared by ultrasonication-assisted successive ionic layer adsorption and reaction(SILAR)process.Morphologies,structures,compositions and photoelectrochemical performances of Bi₂O₃/TiO₂-P NTAs were characterized by scanning electron microscope,transmission electron microscope,X-ray diffraction diffractometer,X-ray photoelectron spectroscopy and electrochemical workstation.Effects of phosphating treatment on the photoelectrochemical performance of TiO₂NTAs are studied.And the deposition process of Bi₂O₃and the photoelectrochemical detection performance of Bi₂O₃/TiO₂-P NTAs were investigated.The results show that the phosphating treatment of TiO₂NTAs can improve the light absorption properties and energy level structure of TiO₂NTAs.And it can also promote the oxidative decomposition of water,thereby improving its photoelectrochemical performance in buffer solution,but it is not conducive to oxidative decomposition of organic matter in water.The modification of Bi₂O₃nanoparticles can effectively promote the direct oxidation of organic matters by photogenerated holes,which improves the response photocurrent,the photoelectrochemical detection performance,and the detection sensitivity of the sensor.The optimized Bi₂O₃/TiO₂-P NTAs achieve a sensitivity of 0.194?A/?M,a detection limit of 7.48?M,and a linear range of 0 to 888.11?M.