Photoelectrocatalytic degradation of p-hydroxybenzoic acid at the surface of a titanium/titanium dioxide nanotube array electrode using electrochemical monitoring

In this study, the titanium/titanium dioxide nanotube array (Ti/TiO2-NTA) electrode was prepared with anodic oxidation of Ti foil electrode. The morphology of Ti/TiO2-NTA electrode was evaluated with scanning electron microscopy images. The results showed that the inner diameter of nanotubes is below of 100 nm. The electrochemical behavior of the as-prepared Ti/TiO2-NTA electrode was studied using the cyclic voltammetry. In addition, a significant photoelectrochemical behavior of the p-hydroxybenzoic acid (p-HBA) was observed on the Ti/TiO2 electrode using the hydrodynamic photoamperometry experiments. Then, the photoelectrocatalytic (PEC) degradation of the p-HBA was performed by this electrode, and compared with photocatalytic (PC), electrooxidation (EC), and direct photolysis by ultra-violet ray. It was found from mechanistic studies that the rate constant for the PEC process of Ti/TiO2-NTA electrode was higher than other degradation processes. The p-HBA concentration monitoring was carried out with the differential pulse voltammetry. Finally, the effects of the solution pH, applied potential, and the p-HBA concentration on the degradation efficiencies were studied and the results showed that the optimum pH for the photoelectrocatalytic degradation was equal to 7.00. The optimum potential and the optimum concentration were about 0.5 V (vs. Ag|AgCl|KCl (3M) as reference electrode) and 0.129 mM in the studied ranges, respectively.