Escherichia coli inactivation by Ti/RuO2-IrO2-TiO2 with different molar ratios obtained by dynamic spin coating: Kinetics and mechanism

In the present work, electrodes based on mixtures of ruthenium, iridium and titanium oxides were used to favor oxygen and/or chlorine evolution reactions, leading to the electro-generation of oxidizing species for the treatment of water contaminated with pathogenic microorganisms. Titanium sheets were modified using the spin coating technique with varying molar proportions of metal oxides to obtain electrodes called MMO1 (RuO2:IrO2: TiO2= 0.25:1:1), MMO2 (RuO2:IrO2:TiO2= 0.75:1:1), MMO3 (RuO2:IrO2:TiO2= 1:1:1), MMO4 (RuO2:IrO2:TiO2= 1:0.75:1) and MMO5 (RuO2:IrO2:TiO2= 1:0.25:1). These were characterized using scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, scanning electrochemical microscopy and linear sweep voltammetry, obtaining homogeneous and electroactive surfaces. Considering the surfaces and electrochemical properties of MMO1 and MMO5, their effectiveness in the inactivation of Escherichia coli (E. coli) was studied in aqueous mediums with NaCl or Na2SO4 as supporting electrolytes. Complete bacterium inactivation was achieved when applying 1.7 mA at initial pH of 7.0 in less than 15 min with both MMOs. Chloride proved more effective than sulfate and treatment time was lower with MMO5 (6 min). Disinfection with Na2SO4 is due to the direct oxidation of E. coli on the surface of MMOs, confirmed by its first-order kinetics and by the absence of lipid peroxidation. For NaCl disinfection results from the direct oxidation of bacteria on the anode surface and the production of active chlorine species. This was confirmed by its pseudo-first order kinetics and by an increase in cell perme-ability, determined by the indirect detection of intracellular enzyme & beta;-D-galactosidase in the aqueous medium.

Automated summary

Electrodes based on mixtures of ruthenium, iridium and titanium oxides were used to treat water contaminated with pathogenic microorganisms. The modified titanium sheets exhibited homogeneous and electroactive surfaces. Both MMO1 and MMO5 electrodes effectively inactivated E. coli, with MMO5 achieving complete bacterium inactivation in only 6 minutes. The disinfection mechanism involved direct oxidation of the bacteria on the electrode surface, with chloride proving to be more effective than sulfate.