Preparation And Photocatalytic Properties Investigation Of TiO₂Photoelectrodes With New Structure

General speaking, TiO2nanotube arrays are often fabricated by anodizing planner metallic titanium foils. As-prepared TiO2nanotubes are attached to the underlying Ti substrate, and their bottom ends are closed. How to increase light absorbance of photocatalyst is an important way to improve the photocatalytic activity of TiO2nanotube arrays. Therefore, in order to improve the photocatalytic activity of TiO2nanotube arrays, two novel TiO2nanoube photoelectrodes are investigated in this paper:ⅰ) TiO2/Ti mesh photoelectrodes with three-dimensional (3D) nanotube arrays; ⅱ) open-ended TiO2nanoube membranes.In this paper we have prepared3D TiO2/Ti mesh photoelectrodes by anodic oxidation. Compared to2D TiO2/Ti foil photoelectrodes, TiO2/Ti mesh photoelectrodes show a significant improvement in photocatalytic activity. This can be demonstrated by about22%and38%enhancement in the degradation efficiency per mass and per area, respectively, when TiO2/Ti mesh electrodes were used to photocatalyze decomposing of methyl orange (MO). The enhanced photocatalytic activity can be contributed to the ability to absorb reflected and refracted light. Furthermore, the effects of different parameters on MO photodegradation were also investigated, such as different calcination temperature, the initial pH value of MO solution, and the present of hydrogen peroxide. The maximum photocatalytic activity could be achieved by the TiO2/Ti mesh photoelectrodes calcinated at550℃. In strong acidic or caustic conditions, such as pH=1or13, a high degradation efficiency can be both obtained. The presence of H2O2in photocatalytic reactions can promote photocatalytic degradation efficiency. Moreover, the experimental results demonstrated the excellent stability of the TiO2/Ti mesh photoelectrodes, and high degradation efficiency could be kept after5times photocatalytic reaction.Open-ended TiO2nanotube membranes were fabricated by acid etching method and raising voltage method, respectively. By comparing the two methods, the raising voltage method has many advantages. Firstly, the raising voltage method eliminates the use for environmentally unfriendly corrosive acidic solutions to open the closed bottoms. Secondly, the method is a one-step process, which can separate TiO2nanotube membranes from the underlying Ti substrate and simultaneously open their bottoms. Finally, the operation of the method is simple, and the size of the opened pores at the nanotube bottom could be readily adjusted by the value and duration of the applied voltage. TG-DSC and XRD experimental results show that the TiO2nanotube membranes start to transform from amorphous phase to anatase at300℃, the phase transformation from anatase to rutile starts at650℃, and completely transform to rutile at900℃. Compared with mix-crystalline open-ended TiO2nanotube membranes, the pure anatase open-ended TiO2membranes have superior photocatalytic activity. As compared to close-ended T1O2membranes, such open-ended TiO2membranes exhibited about2.5times enhancement in photodegradation rhodamine B (RhB).Benefiting from the semiconducting nature and distinctive both-side-open structure, open-ended TiO2nanotube membranes can be used as multifunctional photocatalytic membrane and nanoreactor. As a new photocatalytic membrane, the photocatalytic properties of open-ended TiO2membranes are contributed to RhB concentration reduction during the diffusion process of RhB molecules. As an important nanoreactor, CdS@TiO2core-shell nanocables were successfully fabricated by a simple paired-cell reaction. The growth mechanism of core-shell structure as follows:nucleation-nanotube-nanowire. The Cd2+cations and S2" anions would be absorbed onto the inner wall of nanotubes and heterogeneously nucleate the corresponding CdS nanoparticles. With increased reaction time, the aggregation of CdS nanoparticles continuously occur to form a thin layer on the tube walls, resulting in CdS nanotube. Finally, the wall thickness of CdS nanotubes increases till solid nanowires are obtained. In addition, the photocatalytic experiments show that the CdS@TiO2samples synthesized at24h exhibited about100%enhancement in photocatalytic activity as compared to the bare TiO2nanotubes, while the CdS@TiO2core-shell nanocables synthesized at48h had the equivalent photocatalytic activity to the bare TiO2nanotubes. Such behavior that the photocalytic activity changes with CdS loading amount results from a balance between a larger amount of light absorption and a lower efficiency of charge separation, as well as limited diffusion by channel blocking higher degree of CdS loading.