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This paper reports the characterization and photoactivity of Ag-TiO2materials using different amounts of silver during the hydrothermal synthesis. Photocatalysts were characterized by means of TEM, XPS, XRD, DRS, and N2sorption isotherms to determine the textural properties. The photocatalyst's configuration was observed to be as anatase-brookite mixed phase particles with Ag partially oxidized aggregates on the TiO2surface, which increased visible light absorption of the material. Moreover, photoproduction of singlet oxygen was followed by EPR analysis under visible light irradiations following the formation of TEMPOL. Such photoproduction was totally decreased by using the singlet oxygen scavenger DABCO. Photocatalysts were tested towards the photocatalytic disinfection of water suing a solar light simulator and an interior-light irradiation setup. Results evidenced an increase in the photooxidative effect of TiO2, while dark processes evidenced that part of the inactivation process is due to the Ag-TiO2surface bactericidal effect and possible lixiviated Ag+.

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ResumenSe estudió la cinética de la desinfección fotocatalítica de agua (DFA) con E. coli usando dos ecuaciones cinéticas tipo Langmuir-Hinshelwood de tres parámetros: la constante cinética, la constante de interacción bacteria-fotocatalizador y el coeficiente de inhibición. Se analizó el efecto de la concentración de TiO 2 y la potencia de irradiación sobre los parámetros cinéticos. En los intervalos estudiados, la constante cinética incrementa con el aumento de la concentración del fotocatalizador y de la potencia de irradiación, mientras que, la constante de interacción bacteriafotocatalizador disminuye. Además, el coeficiente de inhibición no presenta dependencia de estas variables. Se usaron medios selectivos para seguir la concentración de bacterias con el fin de evaluar el efecto de la DFA sobre la bacteria y los daños sucesivos que ocurren en ésta hasta llegar a un umbral límite de daño. El modelo cinético utilizado permite la predicción de valores aproximados de las poblaciones bacterianas lastimadas y no lastimadas. Palabras clave: inactivación de bacterias, fotodesinfección, parámetros cinéticos, bacterias lastimadas Kinetics of the Photocatalytic Disinfection of Water contaminated with E. coli. Effect of the Photocatalyst Concentration and of the Irradiation Power AbstractThe photocatalytic water disinfection (PWD) kinetics with E. coli was studied, using two Langmuir-Hinshelwood type kinetic equations involving three parameters: the kinetic constant, the interaction bacteria-photocatalyst constant, and the inhibition coefficient. The TiO 2 concentration and the irradiation power were modified, and their effects on the inactivation kinetics were analyzed. It was found that the kinetic constant increased with the increase of the catalyst concentration and the irradiation power, while the constant related to the interaction bacteria-photocatalyst decreased. In addition, it was found that the inhibition coefficient does not depend on these variables. Furthermore, the bacteria concentration was followed using selective media to assess the effect of the PWD process on the bacteria, and its subsequent attacks to reach a threshold limit of damage. It was observed that the kinetic model predicts approximate values of the undamaged and injured bacteria population.