Tryptophan-modified magnetic graphene oxide for adsorption of copper(II) cation

Recently adsorption by using of modified nano-adsorbents as one of the methods of separating heavy metals from wastewater has been attracted a lot of attention due to the simplicity and high efficiency of the process. In this work, at first a graphene-oxide-based magnetic nanostructure modified by tryptophan was synthesized. The synthesized magnetic graphene oxide has a high absorption capacity for Cu(II) ion (i.e., 118 mg g-1) due to the presence of nitrogen groups of tryptophan exist on the surface of adsorbent. Kinetic parameters and contact time were optimized, and the results showed that the optimal contact time is 60 minutes. Absorption kinetic studies were performed using pseudo-first-order and pseudo-second-order models. The findings indicated that the pseudo-second-order model with a higher regression coefficient (R2=0.9978), compared to the pseudo-first-order model (R2=0.9942), describes the test data better. The adsorption kinetics’ adherence to the pseudo-second-order model demonstrated that the rate-determining step is a chemical interaction. In order to investigate the thermodynamics of absorption, the effects of temperature on the absorption process were explored by using of Van’t Hoff equations, and the results showed that the absorption process is endothermic.