Electrodeposition of WO3 on Ti substrate and the influence of interfacial oxide layer generated in situ: A photoelectrocatalytic degradation of propyl paraben

Ti/TiO2-WO3 photoanode composites were successfully synthesized through a simple electrochemical deposition of WO3 films on Ti substrate. The electrochemical deposition was evaluated in the following periods: 2.5; 5; 10; 20; 30; 45 and 60 min, and led to the generation of the electrodes denoted E2.5; E5; E10; E20; E30; E45 and E60, respectively. The performance of the electrodes was assessed by monitoring the photoelectrocatalytic oxidation of 50 mg L−1 of propyl paraben under UV-Vis light irradiation. Due to its autoxidation, the Ti substrate was found to exert a significant influence over the photoactivity, yielding a thin and photoactive interfacial layer of titanium oxide after heat treatment at 450 °C. More importantly, the photoactivity of the electrodes was strictly dependent on the content of WO3 as well as on its interaction with titanium oxide. In a good synergy of WO3-TiO2 semiconductors, lower amounts of electrodeposited W (<0.8%), as in the case of E2.5 and E5 electrodes, operate as electron scavengers, leading to high photocurrent values. Conversely, larger amounts of W generate centers of charge recombination, resulting in a substantial decrease in photocurrent values. The photoelectrocatalytic application of the best electrode (E2.5) resulted in a complete removal and mineralization of propyl paraben in only 3 h of experiment under optimized conditions (pH 2 and E = +0.5 V). This study is regarded an important step toward the development of photoanodes involving relatively fewer stages. Remarkably, apart from enabling the generation of TiO2 in situ, the method favors the synergy of the semiconductors as it helps to determine the ideal amount of WO3 deposited on the surface of the electrodes.