Role of natural extracts on the synthesis and properties of semiconductor nanoparticles of ZnO applied in water treatment by photocatalytic processes

One of the most pressing issues that the world is currently facing is water contamination. Photocatalysis using semiconductor nanoparticles (NPs) is a promising and potential alternative for water treatment. In this research, zinc oxide (ZnO) NPs were synthesized using Ternstroemia pringlei Rose (FT), Turnera diffusa Willd (DC), and Agastache mexicana (TM) extracts, as an eco-friendly approach. The properties of ZnO NPs were evaluated by different characterization techniques. According to XRD patterns, a hexagonal Wurtzite structure was achieved for all syntheses. FTIR spectra exhibited stretching vibrations of the Zn–O bond at 397 cm⁻¹, which indicates the formation of ZnO. The bandgap was found to vary depending on the extract source. Furthermore, PL spectra showed UV and visible emission associated with free exciton and structural defects in ZnO. A quasi-spherical shape and sizes of less than 20 nm were releveled by SEM and TEM. ZnO NPs, using DC and TM extracts, demonstrated and highlighted the influence in the efficient degradation of Methylene blue (MB), Malachite green (MG), and Congo red (CR); however, the Rhodamine B (RB) and methyl orange (MO), presented a slow degradation independent of the extract used for ZnO synthesis. The green method using FT, DC, and TM extracts offers a suitable route for ZnO production with promising applications in sustainable water treatment.