Dye Photocatalytic Degradation and Water Treatment Using Biosynthetic ZnO Nanoparticles Produced Using Annatto Tree Leaf Extract

The biosynthesis of zinc oxide nanoparticles (ZnO NPs) using plant extracts offers several important advantages, including low residue generation, reduced costs, and potentially faster production as compared to traditional chemical methods. In this study, for the first time, ZnO NPs were biosynthesized using an annatto plant (Bixa orellana) leaf extract and characterized using a range of analytical techniques, including scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, ultraviolet–visible and Fourier transform infrared spectroscopies, thermogravimetric analysis, and point of zero charge measurements, thus ensuring a comprehensive elucidation of their physicochemical properties. Subsequently, photodegradation of methylene blue (MB) dye using the biosynthesized ZnO NPs was successfully demonstrated. The photodegradation studies showed that the ZnO NPs were capable of decomposing over 95% of MB after 110 min of UV irradiation. In addition, the potential application of ZnO NPs for water disinfection was evaluated by assessing their ability to eliminate microbial pathogens. Furthermore, cell-free singlet oxygen and intracellular ROS detection assays were performed to investigate the NP antibacterial molecular mechanisms. Overall, our results reveal that the ZnO NPs exhibit excellent potential for photodegradation applications and may contribute to the development of more effective and sustainable solutions for water treatment and quality control.