Graphene Oxide/Polyamidoamine G4 as a High Efficient and Eco-Friendly Adsorbent for Dichromate Ions

Abstract

In this study, graphene oxide/polyamidoamine G4 was used as a biocompatible nanocomposite adsorbent to adsorb dichromate ions. In alkaline solutions, dichromate ions changed to chromate ions which were not adsorbed on the surface of adsorbent. Thus, experiments were carried out in acidic and neutral water solution. Under these conditions, adsorption sites of adsorbent were protonated by primary and ternary amine groups of adsorbent shown as –NH3+ and –NHR2+ respectively that adsorbed dichromate ions through electrostatic interactions. Adsorption isotherms of dichromate on graphene oxide/polyamidoamine G4 were obtained under various ionic strengths, pHs and temperatures. Isotherms were analyzed by the adsorption isotherm regional analysis (ARIAN) model. The highest observed adsorption capacity of this process was 246.7 mg g–1 at pH = 0 and 318 K. Tests at pH = 2 showed that this process was endothermic. Adsorption kinetic experiments were carried out under various initial dichromate concentrations, pHs, temperatures, shaking rates and ionic strengths and were analyzed by the kinetics of adsorption study in the regions with constant adsorption acceleration (KASRA) model and intraparticle diffusion, ideal-second-order (ISO) and non-ideal process of adsorption kinetics (NIPPON) equations. The four-region ARIAN and KASRA models using a series of equations can interpret thermodynamics and kinetics of interactions of adsorbent and adsorbate under different conditions, respectively. Pb2+, Cd2+, Cr3+ and tannic acid were separated by graphene oxide/polyamidoamine G4 from dichromate ions and the graphene oxide/polyamidoamine G4 was recycled by using an alkaline solution.