Antibacterial activities of gel-derived Ag-TiO<sub>2</sub>-SiO<sub>2</sub> nanomaterials under different light irradiation

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Gel-derived Ag-TiO2-SiO2 nanomaterials were prepared by sol-gel process to determine their disinfection efficiency under UV-C, UV-A, solar irradiations and in dark condition. The surface morphology and properties of gel-derived Ag-TiO2-SiO2 nanomaterials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET specific surface area. The results showed that the average particle size of Ag-TiO2-SiO2 was around 10.9–16.3 nm. SiO2 mixed with TiO2 (the weight ratio of Si to Ti = 10:90) in the synthesis of Ag-TiO2-SiO2 by sol-gel process was found to increase the specific surface area of the obtained photocatalyst (164.5 m2g−1) as compared with that of commercial TiO2(P25) (53.1 m2g−1). Meanwhile, Ag doped in TiO2 (the mole ratio of Ag to TiO2 = 1%) decreased the specific surface area to 147.3 m2g−1. The antibacterial activities of gel-derived Ag-TiO2-SiO2 nanomaterials were evaluated by photocatalytic reaction against Escherichia coli bacteria (ATCC®25922). Ag-TiO2-SiO2 nanomaterials was observed to achieve higher disinfection efficiency than the catalyst without silver since both Ag nanoparticles and ions exhibit a strong antibacterial activity and promoted the e− – h+ separation of TiO2. The bactericidal activity of Ag-TiO2-SiO2 nanomaterial under light irradiation was superior to that under dark and only light. The reaction time to achieve a reduction by 6 log of bacteria of UV-C light alone and Ag-TiO2-SiO2 with UV-C light irradiation were 30 and 5 minutes, respectively. In addition, the superior synergistic effect of Ag-TiO2-SiO2 under both UV-A and solar light as compared to that under UV-C counterpart could be ascribed to the red-shift of the absorbance spectrum of the Ag doped TiO2-based catalyst.