One-step electrosynthesis of visible light responsive double-walled alloy titanium dioxide nanotube arrays for use in photocatalytic degradation of dibutyl phthalate.

Using Ti-6Al-4V (TC4) alloy as a substrate, double-walled alloy titanium dioxide nanotube arrays (DW-ATNTAs) with a special porous inner wall and visible light response are synthesized by an improved anodization method. During the anodization, the V element in the TC4 alloy converts into VO which dominates the visible light response of DW-ATNTAs. After 3 h of irradiation with visible light, there is a nearly 97% reduction of dibutyl phthalate (DBP) by DW-ATNTAs in which the degradation kinetic constant is 50 and 7 times higher than that of titanium dioxide nanotube arrays (TNTAs) and alloy titanium dioxide layers (A-TiO(plate)), respectively. The richly porous inner wall structure of DW-ATNTAs can provide sufficient vacancies for adsorption and active sites for photocatalytic reaction. Furthermore, the differences in the morphology of the inner and outer walls are attributed to the thicker carbon and fluorine-rich oxide layer (C, F-rich oxide layer) resulting from a longer time that the inner wall spends in contact with the electrolyte during the anodization process. This special porous inner wall structure was formed due to the anti-corrosion properties of the alloy caused by appropriate amounts of V and Al as well as the removal of C and F elements during the calcination process.