Highly ordered anodic TiO2 nanotube arrays and their stabilities as photo(electro)catalysts

Highly ordered TiO₂ nanotube arrays with an average diameter of 230 nm, a wall thickness of 30 nm and a length of 1.8 μm were fabricated within a large domain by electrochemically anodizing of a titanium foil in a mixed solution of glycerol and NH₄F aqueous electrolyte. The TiO₂ nanotubes exhibit an anatase structure after annealing at 450 °C in air for 3 h. The direct photolysis (DP), photocatalytic (PC), electrocatalytic (EC) and photoelectrocatalytic (PEC) activities of the TiO₂ nanotube arrays were investigated using methyl orange (MO) as the model pollutant. The degradation of MO in PC process is faster than that in DP process, which confirms the photocatalysis of TiO₂ nanotube arrays. The degradation rate in PEC process is much higher than those in EC and PC processes, which demonstrates the synergetic effect between PC and EC processes. The synergetic factor is 4.1, which suggests that the synergetic effect is strong. Moreover, the stabilities of morphology, structure and photo(electro)catalytic degradation performance of the TiO₂ nanotube arrays were studied in order to evaluate their applicability as photo(electro)catalysts. The photo(electro)catalytic experiments bring neither morphological nor structural modifications to the nanotube arrays. The photo(electro)catalytic degradation rates of the TiO₂ nanotube arrays maintain stable in 10 cycles, which indicates that the TiO₂ nanotube arrays are appropriate to be applied as photo(electro)catalysts.