Emerging trends in phytochemically mediated fabrication of ZnO nanoparticles for the application of harnessing solar light for photocatalytic application to dyes

The present work demonstrates a green route to synthesizing unique-structural-property ZnO nanostructures with enhanced photocatalytic efficiency, utilizing 80 ml of aqueous leaf extract from Azadirachta indica and Moringa oleifera. The crystalline nature of the synthesised ZnO NPs -80-A and M was examined using X-ray diffraction (XRD), where the peak positions at Bragg angles (2θ) of 31.8°, 34.42°, 36.57°, 56.42°, 62.56°, and 66.40° corresponded to Miller indices of (100),(002), (101), (110), (103), and (200), respectively, confirming the hexagonal wurtzite structure; however, the Fourier transform spectroscopy (FT-IR) analysis confirmed the functional groups' purity, and the presence of broad absorption bands appearing at 3340-3400 cm⁻¹ indicated the O-H stretching vibrations of absorbed H₂O molecules, while another strong peak around 476 cm⁻¹ indicated the stretching mode of crystalline ZnO. To examine the photocatalytic activity, 0.1 g/L of ZnO NPs-A and ZnO-NPs-M was immersed in 100 mL of 10 ppm brilliant cresyl blue and Malachite green dye solution, stirred for 25 minutes, and kept in the dark to establish adsorption–desorption equilibrium, followed by open irradiation under sunlight. During irradiation, a 3 ml suspension was taken out at intervals of 20 minutes; the absorbance was measured, which decreased with time. Moreover, the ZnO NPs-A displayed good photocatalytic activity after 160 min of sunlight exposure. The degradation of the dyes followed pseudo-first-order kinetics.