Preparation of TiO2 Nanotube Array on the Pure Titanium Surface by Anodization Method and Its Hydrophilicity

In this work, a highly ordered TiO2 nanotube array on pure titanium (Ti) was prepared by anodization. The effects of the applied voltage and anodization time on the microstructure of the TiO2 nanotube arrays were investigated, and their hydrophilicity was evaluated by the water contact angle measurement. It was found that a highly ordered array of TiO2 nanotubes can be formed on the surface of pure Ti by anodized under the applied voltage of 20 V and the anodization time in the range of 6-12 h, and the nanotube diameter and length can be regulated by anodization time. The as-prepared TiO2 nanotubes were in an amorphous structure. After annealing at 550°C for 3 h, the amorphous TiO2 can be transformed to the anatase TiO2 through crystallization. The anatase TiO2 array exhibited a greatly improved hydrophilicity, depending on the order degree of the array and the diameter of the nanotubes. The sample anodized at 20 V for 12 h and then annealed at 550°C for 3 h exhibited a superhydrophilicity due to its highly ordered anatase TiO2 nanotube array with a tube diameter of 103.5 nm.

Determination of chemical oxygen demand in mixed organic solution by Ti/TiO2 nanotube array electrode method

Chemical oxygen demand (COD) is a significant parameter for analyzing water quality. However, the detection methods still suffer from the problems of secondary pollution, use of harmful substances, complicated operations, etc. To trace these problems, a Ti/TiO2 nanotube array (NTA) electrode was successfully prepared by the secondary anodic oxidation method in this work. The prepared electrode was used to determine COD of single- and multi-component solutions (including aniline, rhodamine B, and potassium hydrogen phthalate). The Ti/TiO2 NTA electrode exhibited higher electrochemical oxidation efficiency than the neat Ti one. The electrocatalytic reactions of the target organics on the electrode surface were confirmed to conform to the first-order kinetic process. Within COD range of 5–150 mg/L, COD value was not only proportional to the anodizing current but also related to organic matter itself. The activation energies of electro-oxidation reaction of different substances were different from each other (An: 14.25 kJ/mol, RhB: 18.56 kJ/mol, and KHP: 35.32 kJ/mol), indicating the differences in their dynamic behaviors on the electrode surface. The related bias obtained for all successive measurements was below ± 5.8%. Therefore, we report a fast, effective, accurate, and well-reproducible COD detection method, which is feasible for both single-component and multiple-component organic solutions.

Development of Graphene-Doped TiO2-Nanotube Array-Based MIM-Structured Sensors and Its Application for Methanol Sensing at Room Temperature

This work concerns the development of a good quality graphene doped TiO2 nanotube array sensor for efficient detection of methanol. A pure and graphene doped TiO2 nanotube array was synthesized by electrochemical anodization. Morphological, structural and optical characterizations were performed to study the samples. Both the nanotube samples were produced in Au/TiO2 nanotube/Ti type MIM-structured devices. Pure and graphene-doped TiO2 nanotubes offered a response magnitude of 20% and 28% to 100 ppm of methanol at room temperature, respectively. Response/Recovery time was fast for the graphene doped TiO2 nanotube array (34 s/40 s) compared to a pure TiO2 nanotube array (116 s/576 s) at room temperature. This study confirmed the notable enhancement in methanol sensing due to the formation of local heterojunctions between graphene and TiO2 in the hybrid sample.