Macroscopic and microscopic insight into the mutual effects of europium(iii) and phosphate on their interaction with graphene oxide

Abstract

Graphene oxide (GO) has been proved to be very efficient for radionuclide enrichment. However, its potential performance for binary sorbate systems containing both a radionuclide and phosphate receives little attention. In this study, the mutual effects of Eu(III) and phosphate on their co-removal processes by GO as a function of contact time, pH and temperature were investigated in detail. The results show that the presence of phosphate can enhance not only the removal amount of Eu(III) but also the removal kinetics of Eu(III) on GO surfaces, and vice versa. Both the external mass transfer and diffusion of solute inside GO are important for the Eu(III) and phosphate co-removal rate. Evaluation of the thermodynamic parameters (ΔG⁰ < 0, ΔH⁰ > 0 and ΔS⁰ > 0) indicates the co-removal process is endothermic and spontaneous. The results of X-ray photoelectron spectroscopy (XPS) and zeta potential (ZP) analyses indicate that the oxygen-containing functional groups on GO surfaces play an important role in the co-removal process. This study provides a quantitative investigation of Eu(III) and phosphate with GO, which can facilitate the assessment of GO as a potential adsorbent for Eu(III) and phosphate simultaneous cleanup.