Effect of adding silver on photocatalytic properties of ZnAl2O4 nanopowder synthesized using microemulsion and polyacrylamide gel methods for recycled water

In recent decades, water purification and removal of organic pollutants such as organic dyes have been among the most important issues. Photocatalyst is one of the most effective methods for recycled water to eliminate organic pollutants and break them down into safe compounds. One of the most significant factors for determining the efficiency of photocatalyst nanoparticles is the utilization of new synthesis methods. Microemulsion and polyacrylamide gel methods are the two methods that were used for the synthesis of zinc aluminate nanoparticles for this study. The powders obtained from these two synthesis methods were characterized using the X-ray diffraction (XRD) technique, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and ultraviolet-visible spectroscopy (UV-Vis) which were utilized as photocatalysts in the photocatalytic degradation reaction of methylene blue (MB). The results demonstrated that the nanoparticles synthesized in both methods were of single-phase zinc aluminate with a spinel structure. The crystallite size obtained for zinc aluminate synthesized using the microemulsion method was 21.7 nm, whereas, in the polyacrylamide gel method, it was 26.3 nm. Microscopic images represented smaller and more uniform particle sizes in the nanoparticles obtained by the microemulsion method. The band gap energy of zinc aluminate nanoparticles obtained using microemulsion and polyacrylamide gel methods was 4.15 and 3.82 eV, respectively. Similarly, the results of MB removal showed that zinc aluminate nanoparticles synthesized using the microemulsion method and polyacrylamide gel, respectively, were 100% and 71% after 120 min. In the second phase of this study, silver nanoparticles were added to zinc aluminate nanoparticles during the synthesis process. X-ray diffraction showed that silver nanoparticles are formed metallically next to zinc aluminate. Moreover, the addition of silver decreased the crystallite size and slightly increased the band gap energy of zinc aluminate. The results of MB dye degradation tests in the presence of ZnAl2O4-Ag nanocomposites showed that the kinetics of dye degradation increased when the silver increased up to 5 wt%. Finally, the mechanism studied on dye degradation using scavenger agents showed that the main agents of dye degradation are the superoxide radical and the holes created in the valence band. It was consistently confirmed by examining the valence and conduction band potentials and also by comparing these potentials with those responsible for producing superoxide and hydroxyl radicals.