Adsorption of uranium by phosphorylated graphene oxide

Abstract

A novel phosphorylated graphene oxide (PGO) adsorbent material was synthesized by chemical grafting. The morphology and structure were characterized by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The Fourier transform infrared spectroscopy (FT-IR) spectrum, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to investigate the functional groups on the surface of adsorbents. It was confirmed that the phosphate groups were introduced onto the surface of graphene oxide by reacting with C–O–C. In addition, the effect of environmental factors including pH, ionic strength, temperature, and contact time for the adsorption of U(VI) were investigated by batch experiments. The U(VI) sorption process of PGO was clearly pH-dependent, showing that the adsorption was driven by complexes between the interior surface of PGO and uranyl ions. The adsorption process was dominanted by the Langmuir isotherm model and the pseudo-second-order model, indicating that chemisorption controlled the adsorption. The adsorption capacity of U(VI) onto PGO reaches 396.83 mg g−1, that is significantly higher than that of the GO (249.38 mg g−1). The selectivity was above 56%. The adsorption thermodynamic model calculation indicated that the sorption process was endothermic and spontaneous. The 0.1 mol L−1 HCl solution was selected as elution solvent for the study of reusability of PGO, and the desorption rate reaches 98%. After the five adsorption-desorption cycles, the absorption of PGO was decreased only 13%, demonstrating that PGO maintains excellent repeatability.