Ag-ZnO nanocomposites with photocatalytic and antimicrobial properties obtained by green synthesis in Ulva lactuca aqueous extract

Abstract Ulva lactuca is a valuable source of biomolecules and therefore an important resource in the green synthesis of metals, metal oxides, or composite materials. In this study, we obtained Ag(0) nanoparticles by green synthesis in the U. lactuca extract and incorporated them into zinc oxide nanopowder in order to improve the properties of ZnO for application in wastewater treatment. The molar ratio in the synthesis of Ag-ZnO nanocomposites was 1:50, 1:20, and 1:10, and the synthesis followed two routes, differing in the obtaining of the colloidal Ag(0), i.e., in basic, respectively neutral U. lactuca extract. The U. lactuca extract was not only used as a reaction medium but also served as a source for the reduction agent in producing Ag nanoparticles and capping biomolecules. The resulting nanocomposites underwent analysis via various techniques such as X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, UV–visible diffuse reflectance, Fourier transform infrared, and photoluminescence spectroscopy, and the BET method was used for the determination of the specific surface area. The results revealed that the synthesis route leads to differences in morphology and composition. The efficacy of the obtained composites in removing Congo Red and levofloxacin from aqueous solutions was evaluated, revealing a higher removal efficiency (over 90%) for the dye compared to levofloxacin (around 40%). The antimicrobial properties of Ag-ZnO composites were tested against Gram-positive and Gram-negative bacteria, and biocompatibility was evaluated against normal cells (normal human lung fibroblast cells).