Adsorption of acid yellow 36 onto green nanoceria and amine functionalized green nanoceria: Comparative studies on kinetics, isotherm, thermodynamics, and diffusion analysis

In this study, the green nanoceria (GN) was synthesized from Prosopis juliflora (Sw.) leaves extract, then amine functionalized to GN-NH2 (AGN) with epichlorohydrin and ammonium hydroxide. The synthesized GN and AGN were characterized by FT-IR, zeta potential, XRD, BET model and.HR-TEM. Sequentially, Acid Yellow 36 (AY36) was adsorbed onto the GN and AGN in aqueous solutions in batch trials by varying the pH, initial adsorbate concentration and contact time. Further, the equilibrium kinetics, isotherm, thermodynamics, and diffusion analysis were probed for the experimental data. In the ambient temperature and at acidic pH of 2, the maximum removal efficiency of AY36 is 73.3 and 92.9% for GN and AGN respectively. The kinetic data exhibited good correlation coefficient (r(2) > 0.99) for the pseudo-second-order and elovich models with marginal error values signifying the chemisorption type of adsorption process. Moreover, the equilibrium data suggesting the monolayer coverage of adsorbate as it fits well with the Langmuir isotherm model (r(2) > 0.99) and the maximum adsorption capacities of GN and AGN are 16.39 and 26.95 (mg/g), respectively. The energy functions of chemical thermodynamics revealed the adsorbate transport across the phase boundary is of spontaneous and endothermic. Diffusional models demonstrated that the intra-particle diffusion controls the rate and dominates the external boundary layer diffusion. Further, the study proposed the electrostatic interactions or surface complexation might facilitate the AY36 adsorption onto AGN. The potential restorative ability of the adsorbents was proved by desorption studies and thus identifies them as effective adsorbents for the removal of AY36 from aqueous solutions. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.