Fabrication and photocatalytic properties of free-standing TiO2 nanotube membranes with through-hole morphology

Anodic growth of TiO2 nanotubes has recently attracted intensive interests. However, the insulating, closed barrier layer has restricted their feasibility for the applications such as flow-through photocatalytic reactions, biofiltration, and diffusion controlling. In the present work, we fabricated free-standing TiO2 membranes with through-hole morphology by elevating the anodizing voltage at the end of anodization process. Characterization of the samples was carried out by means of scanning electron microscope, X-ray diffraction and thermogravimetry-differential scanning calorimetry. The experimental results show that the TiO2 membranes start to transform from amorphous phase to anatase at 300 °C, and the phase transformation from anatase to rutile starts at 650 °C. In addition, photocatalytic degradation of rhodamine B by the TiO2 membranes with closed bottoms and opened bottoms has also been systematically investigated. As compared to TiO2 membranes with closed bottoms, TiO2 membranes with opened bottoms exhibited superior photocatalytic activity due to its better access for rhodamine B molecules as well as the enhanced light harvesting and electron collection efficiencies.

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► The closed bottoms were opened by elevating the anodizing voltage.
► Phase transformation from anatase to rutile starts at 650 °C.
► TiO2 membranes in the anatase form have a better catalytic performance.
► Opened-bottom TiO2 membranes with exhibited superior photocatalytic activity.