A novel eco-friendly procedure was developed to adsorb Pd2+ ions from wastewaters using the green synthesized zinc oxide (ZnO) nanoparticles (NPs). ZnO NPs were easily produced using zinc nitrate through Centaurea cyanus extract as a reducing agent at ambient conditions. X-ray diffraction results demonstrated that ZnO NPs have a highly crystalline hexagonal structure. Fourier transform infrared spectral analysis indicated an active contribution of C. cyanus-derived biomolecules in zinc ions bioreduction. ZnO NPs were properly dispersed and had a hexagonal shape. The impact of process parameters like initial pH of solution, adsorption dosage, Pd2+ ions initial concentration, and contact time on the Pd2+ ions adsorption from the effluent of a petrochemical company was evaluated. The Freundlich isothermal model could excellently legitimize a multilayer adsorption. The adsorption process followed a pseudo-second-order reaction kinetic, i.e., chemisorption process
