TiO2–carbon nanotube heterojunction arrays with a controllable thickness of TiO2 layer and their first application in photocatalysis

TiO2–carbon nanotube (CNT) heterojunction arrays on Ti substrate were fabricated by a two-step thermal chemical vapor deposition (CVD) method. CNT arrays were first grown on Ti substrate vertically, and then a TiO2 layer, whose thickness could be controlled by varying the deposition time, was deposited on CNTs. Measured by electrochemical impedance spectroscopy (EIS), the thickness of the TiO2 layer could affect the photoresponse ability significantly. About 100 nm thickness of the TiO2 layer proved to be best for efficient charge separation among the tested samples. The optimized TiO2–CNT heterojunction arrays displayed apparently higher photoresponse capability than that of TiO2 nanotube arrays which was confirmed by surface photovoltage (SPV) technique based on Kelvin probe and EIS. In the photocatalytic experiments, the kinetic constants of phenol degradation with TiO2–CNT heterojunctions and TiO2 nanotubes were 0.75 h−1 (R2 = 0.983) and 0.39 h−1 (R2 = 0.995), respectively. At the same time, 53.7% of total organic carbon (TOC) was removed with TiO2–CNT heterojunctions, while the removal of TOC was only 16.7% with TiO2 nanotubes. These results demonstrate the super capability of the TiO2–CNT heterojunction arrays in photocatalysis with comparison to TiO2-only nanomaterial.