Photocatalytic inactivation of E. Coli by ZnO–Ag nanoparticles under solar radiation

Abstract

Porous and fluffy ZnO photocatalysts were successfully prepared via simple solution based combustion synthesis method. The photocatalytic inactivation of Escherichia coli bacteria was studied separately for both Ag substituted and impregnated ZnO under irradiation of natural solar light. A better understanding of substitution and impregnation of Ag was obtained by Raman spectrum and X-ray photoelectron analysis. The reaction parameters such as catalyst dose, initial bacterial concentration and effect of hydroxyl radicals via H 2 O 2 addition were also studied for ZnO catalyst. Effective inactivation was observed with 0.25 g/L catalyst loading having 10 9 CFU/mL bacterial concentration.With an increase in molarity of H 2 O 2 , photocatalytic inactivation was enhanced. The effects of different catalysts were studied, and highest bacterial killing was observed by Ag impregnated ZnO with 1 atom% Ag compared to Ag substituted ZnO. This enhanced activity can be attributed to effective charge separation that is supported by photoluminescence studies. The kinetics of reaction in the presence of different scavengers showed that reaction is significantly influenced by the presence of hole and hydroxyl radical scavenger with high efficiency.Successful synthesis of hexagonal wurtzite ZnO was carried having BET surface area of 16.8 m 2 /g. A modification to ZnO was performed by Ag substitution and impregnation bearing surface area of 14.2 m 2 /g and 12.4 m 2 /g, respectively. Substitution and impregnation of silver as Ag + ion and metallic Ag was confirmed from XPS. The photocatalytic tests showed that Ag impregnated ZnO exhibits excellent bacterial inactivation. The porous and open structure of ZnO favored the effective inactivation by increasing the number of active sites and effective charge separation observed in presence of Ag. Ag acts as an electron sink and hole as hydroxyl radical former for the photochemical killing of bacteria. The experiments for different radical and electron-hole trapping showed that the photogenerated holes and ·OH radicals are the main oxidative species for E. coli inactivation.

Structure, morphology and luminescence properties of sol-gel method synthesized pure and Ag-doped ZnO nanoparticles

“…Photoluminescence spectroscopy is used for the essential interpretation of chemical compositions, structure, impurities, energy transfer, photoelectric activity and electronic structure of nanoparticles. In this study of pure ZnO and Ag-doped ZnO nanoparticles, the obtained PL emission intensity decreased and these results are in good agreement with the stern-Volmer quenching [31]. Further a highly significant charge carrier separation efficiency was recorded and also some controversial defect emission in ZnO.…”

Synergistic Enhancement in Antibacterial Activity of Core/Shell/Shell SiO2/ZnO/Ag3PO4 Nanoparticles

“…Gao et al . synthesized graphene oxide−ZnO−Ag for disinfection of E. coli under visible‐light, with a material dose of 100 μg/ml for killing 10 7 CFU/ml E. coli ; Adhikari et al . used 200 μg/ml ZnO−Ag nanoparticles to treat 10 6 CFU/ml E. coli .…”

“…Previous studies on integrating Ag with ZnO nanoparticles [51,52] or nanorods [53] revealed that Ag introduction could greatly enhance the photo-antibacterial ability by narrowing the bandgap of ZnO, but also bring the pristine toxicity of Ag. Gao et al [53] synthesized graphene oxideÀZnOÀAg for disinfection of E. coli under visible-light, with 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 a material dose of 100 mg/ml for killing 10 7 CFU/ml E. coli; Adhikari et al [54] used 200 mg/ml ZnOÀAg nanoparticles to treat 10 6 CFU/ml E. coli. In our study, 60 mg/ml SZA-NPs can kill~5 10 8 CFU/ml E. coli in suspension.…”

Insights into the Photocatalytic Bacterial Inactivation by Flower-Like Bi2WO6 under Solar or Visible Light, Through in Situ Monitoring and Determination of Reactive Oxygen Species (ROS)

“…The effect of the initial concentration on the E. coli kinetics mediated by Bi 2 WO 6 catalysts is presented in Figure 7b, showing a delay in the time necessary for bacterial inactivation at higher bacterial concentrations. Although this effect can be ascribed to the exhaustion of surface active sites due to opacity in solution [43], we note here that in absolute numbers, the higher the amount of bacteria in solution, the higher the number of available bacteria (for inactivation). Hence, by calculating the amount of cells inactivated in 4 h per mg of catalyst and per minute, we get 2075, 208, and 21 cells min −1 mg −1 for 10 8 , 10 7 , and 10 6 , respectively.…”