Polylysine Functionalized Graphene Aerogel for the Enhanced Removal of Cr(VI) through Adsorption: Kinetic, Isotherm, and Thermodynamic Modeling of the Process

Abstract

The amine functionalized graphene aerogel (GAFP) was prepared by using polylysine as an amine-rich cross-linker with the graphene oxide. The prepared GAFP aerogel was characterized by various analytical techniques including FT-IR spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, X-ray diffraction, and Brunauer-Emmett-Teller (BET). The as-prepared GAFP aerogel showed an excellent uptake capacity (170.64 ± 9.69 mg/g) for Cr(VI) which was much greater as compared to recently reported graphene-based adsorbents. The kinetics of Cr(VI) adsorption on the GAFP followed the pseudo-second-order model. The mechanism of adsorption was explored through various diffusion models such as Mckay et al., Waber-Morris, and Richenberg which revealed that the external diffusion and intraparticle diffusion governed the rate of Cr(VI) adsorption. The isotherm studies confirmed that the Cr(VI) chemically adsorbed on the GAFP in monolayer fashion which was consistent with the electrostatic interaction between oxyanions and protonated amine groups. The process of Cr(VI) adsorption was found to be thermodynamically spontaneous and endothermic. © 2017 American Chemical Society.