Controlled synthesis and enhanced photoelectro-catalytic activity of a 3D TiO2 nanotube array/TiO2 nanoparticle heterojunction using a combined dielectrophoresis/sol–gel method

The surface morphology, particle size and crystal structure have a great impact on the performance of materials. Therefore, it is necessary to explore a method for the controllable synthesis of materials. In this study, three-dimensional TiO2 nanotube arrays (3D-TNAs) formed by electrochemical anodization over Ti meshes have been prepared. The TiO2 nanotubes are oriented in all directions, and could harvest the incident light from any direction. 3D TiO2 nanotube arrays decorated by TiO2 nanoparticles (3D-TNAs/TiO2) were successfully prepared by a combined dielectrophoresis (DEP)/sol–gel process. This method greatly shortens the time required for 3D-TNAs/TiO2 preparation while increasing the density of electrode materials and particle size uniformity. Experimental results show that the morphology and size of 3D-TNAs/TiO2 can be controlled using DEP technology. These mesh electrodes with an anatase/rutile heterojunction were applied in photoelectrocatalytic degradation of methylene blue (MB), and show a significant improvement in photoelectrocatalytic activity compared to unmodified 3D-TNAs and 3D-TNAs/TiO2 fabricated through only a sol–gel process. The photocurrent density could reach 0.11 mA cm−2. The superior photoelectrocatalytic activity and the photocurrent response of 3D-TNAs/TiO2 were mainly attributed to the high specific surface area, strong light absorption, low electron–hole recombination rate and wide light-response range.