Photoelectrochemical degradation of 2,4-dichlorophenoxyacetic acid using electrochemically self-doped Blue TiO nanotube arrays with formic acid as electrolyte.

Blue TiO nanotube arrays (Blue-TNTs) were fabricated via an electrochemical reduction method with formic acid as the electrolyte. The optimum reduction conditions were obtained as bias potential of -1.3 V, reduction time of 5 min and formic acid of 3 M. Blue-TNTs were remarkably corroded compared with the intact TNTs. Similar crystal structures of the two catalysts were observed using X-ray diffraction, while red-shift was observed for Blue-TNTs using Raman spectra. X-ray photoelectron spectroscopy indicated of the presence of Ti in Blue-TNTs that resulted from the reduction of Ti and reduced the resistance of the catalyst. Blue-TNTs exhibited much stronger light-absorption than intact TNTs over the entire ultraviolet-visible region, especially in the visible region. The catalyst was used toward the photoelectrochemical oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) for the first time where the influencing factors were studied. Photoelectrocatalysis with Blue-TNTs presented a 2,4-D degradation rate constant (0.0295 min) more than twice the sum of that of electrocatalysis (0.0055 min) and photocatalysis (0.0089 min). Blue-TNTs fabricated in formic acid showed a better photoelectrocatalytic performance for 2,4-D removal compared with that prepared in ethylene glycol, NaSO and NaNO solution. Blue-TNTs is considered to be a promising photoelectric anode for contaminant degradation.