Green synthesis of ultrafine zinc oxide nanoparticles for photocatalytic degradation of methylene blue dye: Optimization and kinetic studies

• Sustainable green synthesis was used to synthesize ultrafine ZnO NPs with uniform morphologhy. • Phyllanthus acidus leaf extract was utilized as reducing and capping agent. • Ultrafine ZnO NPs exhibited high surface area of 21.2016 m 2 /g with a mean particle size of 22 nm. • ZnO NPs exhibited 72% degradation efficiency against methylene blue dye under ultraviolet light illumination. • Optimization of dye, catalyst and oxidants & reaction kinetics were investigated and discussed. . Zinc oxide nanoparticles (ZnO NPs) were synthesized using Phyllanthus acidus leaf extract by means of its reduction and stabilization tendency. The prepared ZnO NPs were systematically characterized by X-ray diffraction, Brunauer–Emmett–Teller, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and UV-Visible diffuse reflectance spectroscopy techniques. X-ray diffraction analysis confirmed the development of ZnO NPs with hexagonal wurtzite structure. Rietveld refinement analysis disclosed consistency of lattice parameters (a and c) and cell volume with the hexagonal wurtzite structure. Observed R p , R wp and χ 2 values indicated better profile refinement of ZnO NPs. According to field emission scanning electron microscopy and transmission electron microscopy analyses, the ZnO was composed of ultrafine nanoparticle morphology with size ranged between 15 and 30 nm and a mean particle size of 22 nm. Brunauer–Emmett–Teller analysis was employed to evaluate texture features of ZnO NPs and determined their surface area (21.2016 m 2 /g). Optical analysis disclosed that the green synthesized ZnO NPs had band gap energy value of 3.21 eV. The ZnO NPs were effectively utilized for photodegradation of methylene blue dye under ultraviolet light illumination and achieved a maximum efficiency of 72% at 90 min. The insights of green synthesizing ZnO NPs and their photodegradation application are thoroughly explained in detail.