Development of titania nanotube arrays: The roles of water content and annealing atmosphere

The effect of water content in the electrolyte solution during annealing process in the synthesis and modification of titania nanotube arrays (TNTAs) by anodic oxidation process has been investigated. Variations in annealing technique that leading to some specific properties of the TNTAs produced have been examined. Doped-TNTAs were obtained by the in-situ anodic oxidation method in glycerol containing fluoride solution followed by annealing to induce crystallization. FESEM and SEM results indicated that TNTAs with inner diameters of 49-80 nm, wall thicknesses from 28 to 42 nm and lengths from 1407 to 1570 nm were synthesized. At water content of 25 v% in the electrolyte solution, self-organized with vertical, ordered of TNTAs with relatively uniform diameter was observed. Suitable morphology of TNTAs such as well developed tubes, vertically oriented, highly ordered, long with optimal diameter and wall thickness of TNTAs could suppress recombination of electrons-holes and, therefore, increase photoelectrochemical properties. Annealing with H2/Ar is found to be efficient for introducing dopant C and N into the lattice of TNTAs to form Ti-O-C and N-Ti-O (FTIR analysis). Therefore, the reducing band gap can be obtained (UV-Vis DRS analysis). Annealing under H2/Ar of as-synt TNTAs with water content of 25 v% in the electrolyte solution produced anatase phase (XRD analysis) and showed optimal condition in producing the highest photocurrent density.