Studying structural, morphological and optical properties of nanocrystalline ZnO:Ag films prepared by sol-gel method for antimicrobial activity

Pure and Ag-doped zinc oxide sol-gel thin films were prepared by spin-coating process. Pure and Ag-ZnO films, containing 2-8% Ag, were annealed at 500 A degrees C for 2 h. All thin films were prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-visible spectroscopy. X-ray diffraction studies show the polycrystalline nature with hexagonal wurtzite structure of ZnO and Ag:ZnO thin films. The crystallite size of the prepared samples reduced with increasing Ag doping concentrations. AFM and SEM results indicated that the average crystallite size decreased as Ag doping concentration increased. The transmittance spectra were then recorded at wavelengths ranging from 300 to 1000 nm. The films produced yielded high transmission at visible regions. The optical band gap energy of spin-coated films also decreased as Ag doping concentration increased. In particular, their optical band gap energies were 3.75, 3.55, 3.4, 3.3, and 3.23 eV at 0%, 2%, 4%, 6%, and 8%, respectively. Antibacterial activity of pure and Ag-doped zinc oxide against Escherichia coli and Staphylococcus aureus was evaluated by international recognized test (JIS Z 2801). The results showed that pure and Ag-doped ZnO thin film has an antibacterial inhibition zone against E. coli and S. aureus. Gram-positive bacteria seemed to be more resistant to pure and Ag-doped ZnO thin film than gram-negative bacteria. The test shows incrementally increasing in antibacterial activity of the thin films when dopant ratio increased under UV light. [GRAPHICS] Pure and Ag-doped zinc oxide sol-gel thin films were prepared by spin coating process. Pure and Ag-ZnO films, containing 2-8% Ag, in comparing with other researchers, Ag was added to the ZnO thin films with high concentration. It was found that Ag concentration was affected on surface roughness, grain size, absorption of UV light and antibacterial activity of the samples. The antibacterial activity of pure and Ag doped ZnO thin films improved under UV light for 1 h at room temperature. The presence of the silver in zinc oxide structure enhanced the antibacterial activity up to 99.32% against S. aureus and E. coli at 6% Ag-ZnO prepared films. All prepared films have hexagonal wurtzite structure. Moreover, the antibacterial activity of thin films against S. aureus under UV light irradiation (365 nm, 8 W) has been developed in this research.