An investigation of photoelectrocatalytic disinfection of water using titania nanotube photoanodes with carbon cathodes and determination of the radicals produced

In photoelectrocatalysis (PEC) a considerable amount of research has been focused on improving the photoelectrode; however, cathodic reactions are essential to PEC disinfection. In this work, a TiO2 nanotube (TiNT) array was used as the photoanode with various cathode electrodes materials, including gas diffusion electrodes (GDE) modified with different Pt nanoparticle loadings. The highest rate of E.coli inactivation was achieved with the non-modified GDE (2.51 log) compared to Pt mesh paddle (0.79 log reduction). This was explained by the examining reactive oxygen species generated at the counter electrode, where the non-modified GDE had the highest Faradaic efficiency of 15.5% for the formation of H2O2. Modification with Pt inhibited the formation of H2O2 to below the detection limit. The TiNT photoanode was shown to generate hydroxyl radicals, but importantly, there was reduction of molecular oxygen to superoxide radical at the anode. A thin cell reactor was then constructed using the identified optimal materials and a 5.0 log reduction in E.coli was in 20 min under UVA irradiation.