Fabrication and characterization of graphene oxide and reduced graphene oxide decorated diatomite composite materials and their adsorption performance for uranium ions

In this study, the composite materials based on the incorporation of diatomite of graphene oxide (GO)/reduced graphene oxide (rGO/diatomite) were developed and characterized by different techniques (SEM, XRD, FTIR and BET). Developed composites were used for the first time in the removal of uranium ions from aqueous solutions. In adsorption studies, parameters affecting the adsorption efficiency such as solution pH, temperature, contact time and initial U(VI) concentration were investigated using full factorial experimental design (FFED). ANOVA (analysis of variance) analysis within the 95 % confidence interval of the model applied to control the compatibility of the model and the experimental findings was examined. Langmuir, Freundlich and Temkin isotherms were used to determine the adsorption model and related parameters were calculated. In addition, adsorption thermodynamic parameters such as enthalpy, Gibbs free energy change and entropy were calculated. The uranium removal behaviour on GO/diatomite and rGO/diatomite was better characterized by the pseudo-second order and Langmuir models, indicating that uranium ions were chemically adsorbed onto composite materials. Additionally, it was observed that higher temperatures promoted the uranium removal on GO/diatomite and rGO/diatomite, suggesting that the removal process was a spontaneous endothermic and exothermic reaction, respectively. In addition, the adsorption of U(VI) with GO/diatomite and rGO/diatomite was investigated using density functional theory (DFT) study. Configuration and adsorption energy were determined. The GO/diatomite composite materials can be a promising candidate as an adsorbent for the removal of uranium from aqueous solutions.