Photoelectrocatalytic inactivation of Pseudomonas aeruginosa using an Ag-decorated TiO2 photoanode

Abstract

Fast and total inactivation of Gram-negativePseudomonas aeruginosain suspensions at natural pH 5.9 has beenachieved by photoelectrocatalyisis (PEC), using Ag-decorated TiO2photoanodes onto transparent conductingindium tin oxide (ITO) under UVA irradiation. The assays were made with 100 mL of bacterial suspensions in anundivided cell equipped with a photoanode, a stainless steel cathode and Ag|AgCl (3 M KCl) as referenceelectrode. Total inactivation was obtained in only 5 min using coatings with 4 wt.% Ag, 25 mM Na2SO4as theelectrolyte and 1.70 V as applied bias potential. Comparative photocatalytic treatments reached total inactiva-tion at much longer time, suggesting the crucial role of hydroxyl radicals in PEC. These oxidants, which weredetected by electron spin resonance, attacked the outer cell wall very effectively, since the recombination of theelectron/hole pairs photoinduced under UVA irradiation was reduced. As characterized by high-resolutiontransmission electron microscopy (HRTEM), the best synthesized Ag-TiO2thin-film photoanode mainly containsanatase TiO2nanopowder decorated with Ag nanoparticles of ca. 45 nm. Analyses by X-ray powder diffractionand UV/Vis spectroscopy were also performed. The potential use of PEC for bacterial disinfection was confirmedfor the rod-shaped Gram-positiveBacillus atrophaeus, which was more slowly inactivated due to its different cellwall structure. Scanning electron micrographs of both bacteria showed that PEC induced a high roughness, celllysis and accumulation of cellular debris.