Photoelectrocatalytic destruction of organics using TiO 2 as photoanode with simultaneous production of H 2O 2 at the cathode

Abstract

Research on the photoelectrocatalytic (PEC) oxidation of organic contaminants, the role of cathodes during photocatalysis has usually been disregarded. This paper reports a study of the PEC decomposition of aniline and salicylic acid with simultaneous production of hydrogen peroxide in a divided reactor using TiO 2 as a photoanode. Two types of TiO 2 electrode were used. Thermal oxidation electrodes (TO–TiO 2) were made by oxidation of titanium metal sheet; sol–gel electrodes (SG–TiO 2) were made by coating and then heating a layer of titania gel on titanium sheet. Saturated photocurrent was used to carry out an initial characterization and optimization of both electrode types. The best TO–TiO 2 electrodes were prepared by heating titanium at 600–700 °C in air. For the SG–TiO 2 electrodes, optimum performance was obtained by heating at 500 °C. These electrodes were then used to photodegrade aniline and salicylate. The SG–TiO 2 electrodes turned out to be superior to the TO–TiO 2 electrodes in terms of PEC rate under the same conditions but the difference in rate between the two electrodes was comparable under a high enough bias potential. The most important factors affecting the production of H 2O 2 in the cathode compartment are presented. The current efficiencies for the accumulation of H 2O 2 were remarkably affected by the cathode used, pH value, current density, and metal cations such as copper and iron ions. An expected H 2O 2 concentration could be obtained by controlling either the magnitude of the photocurrent or illumination time. The maximum current efficiency for the cathodic reduction of oxygen to H 2O 2 was as high as 90.1% when graphite was used as the cathode. Compared to the SG–TiO 2 electrode, the TO–TiO 2 electrode had a higher light to electricity conversion efficiency, thus it turned out to be more suitable for the production of H 2O 2. Furthermore, the role of in-situ reduced oxygen species in the PEC decomposition of aniline was evaluated.