Hydrothermal synthesis of ZnO nanoparticles and comparison of its adsorption characteristics with the natural adsorbent (mango peel)

This study focuses on the utilization of ZnO (as synthetic) and mango peel (natural adsorbent)  to remove blue 221 dye from aqueous solutions. First, ZnO nanoparticles (NPs) were synthesized and detected using the descriptor-based techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), N2 adsorption/desorption isotherms (BET), and X-ray diffraction (XRD). Various operational parameters including adsorbent concentration, pH, adsorbent dose, contact time, and stirring speed were investigated. The obtained kinetic results demonstrated great compatibility of the pseudo-second-order model with the experimental data. The effects of thermodynamic parameters were calculated to confirm the endothermic, spontaneous and physical nature of adsorption process. Langmuir and Freundlich isotherm models were utilized to fit the obtained equilibrium data. Freundlich model was found sufficient to explain the adsorption of blue 221 dye by ZnO NPs and mango peel. The results indicated that the ZnO NPs performed better in blue 221 dye removal as compared with mango peel. The mean size of ZnO NPs was found to be 22.16 nm. The specific surface area of ZnO NPs was obtained 26.85 m2.g-1 and pore volume and pore-size were 0.0581 cm3.g-1 and 1.22 nm, respectively. The maximum adsorption capacity of blue 221 dye on ZnO NPs and mango peel was estimated as 133.33 and 476.19 mg.g-1, respectively.