Synthesis of a three-dimensional reduced graphene oxide aerogel decorated with (Fe3O4@SiO2–NH2)–COC2H4COOH for adsorption of heavy metal cations

Abstract

Hereunder, a new method for the synthesis of a three-dimensional (3D) reduced graphene oxide (r-GO) nanohybrid is presented by the use of a synthetic novel crosslinker ((Fe3O4@SiO2–NH2)–COC2H4COOH) designed for multifunctional purposes. This crosslinker not only provide a three-dimensional structure for the adsorbent (increasing adsorption capacity), but also it enables the magnetically separation of the 3D r-GO nanohybrid. According to high-resolution transmission electron microscopy (HRTEM), the r-GO sheets were well decorated with nearly spherical (Fe3O4@SiO2–NH2)–COC2H4COOH nanoparticles with an average size of 60 nm. More importantly, the X-ray photoelectron spectroscopy (XPS) showed that the 3D r-GO nanohybrid contains several oxygenous and nitrogenous functional groups that makes it an ideal heavy metallic cations adsorbent. In addition, the synthesized 3D r-GO nanohybrid showed a maximum adsorption capacity of ∼455, 448 and 232 mg/g for lead, cadmium, and copper, respectively; besides, the exothermic adsorption of these cations followed a pseudo-second-order model. It was also found that an effective metal desorption step can be achieved by using a mixture of nitric acid and acetonitrile. The adsorption percentage of the 3D r-GO nanohybrid remained unchanged after five cycles of adsorption–desorption step. At last, the experimentally observed adsorption/desorption behaviors were justified using the density functional theory (DFT).