A facile green synthesis of ZnO nanoparticles and its adsorptive removal of Congo red dye from aqueous solution

Abstract

In this present article, zinc oxide nanoparticles (NPs) have been synthesized by a greener approach using Acacia concinna fruit extract via sol–gel technique. These biosynthesized ZnO NPs were characterized by XRD, SEM, FTIR, BET and HRTEM techniques. The XRD pattern revealed the samples are crystalline and having hexagonal ZnO phase with wurzite type structure. The morphology of zinc oxide nanoparticles were analysed by SEM, which suggested that the particles are in agglomerated form and porous in nature. The adsorption of Congo red dye by using these ZnO NPs was investigated extensively. The kinetics, thermodynamics and adsorption isotherm data were obtained from the batch experiment analysis of the Congo red dye, where the efficiency of adsorption of the sample was found to be ∼ 92%. The kinetics data analysis, indicated the adsorption process to be of pseudo-second order type. The Freundlich isotherm was found to be best fitted with R2 = 0.998, signifying a multilayer adsorption. Thermodynamic parameters, ΔH0 and ΔS0 were calculated. The negative value of ΔH0 (−5.644 kJ/mol) corresponded to an exothermic adsorption process and the positive value of ΔS0 (0.0108 J mol−1 K−1) signified the increased randomness at the interface of the adsorbate and the adsorbent.