One-Pot Synthesis of LDH/GO Composites as Highly Effective Adsorbents for Decontamination of U(VI)

The removal mechanism of U(VI) on Mg-Al-layered double hydroxide-supported graphene oxide (LDH/GO) composites was investigated by batch, spectroscopic, and surface complexation modeling. The batch experiments showed that the enhanced removal of U(VI) on LDH and LDH/GO composites in the presence of carbonate was observed at pH < 5.0, whereas the presence of carbonate significantly inhibited U(VI) removal at pH starting from 7.0 to 9.0. It is demonstrated that the oxygenated functional groups (i.e., -OH) were responsible for the high effective removal of U(VI) by XPS analysis. The results of XANES and EXAFS spectra indicated that adsorption of U(VI) on LDH/GO composites was inner-sphere surface complexation. According to surface complexation modeling, the removal of U(VI) on LDH/GO composites can be satisfactorily fitted by a diffuse layer model with an ion exchange (X2UO2) and two inner-sphere surface complexes (SOUO2+ and SOUO2(CO3)(2)(3-) species). The maximum adsorption capacities of LDH and LDH/GO composites calculated from the Langmuir model at pH 4.5 and T = 293 K were 99.01 and 129.87 mg/g, respectively. These findings indicated that GO-based composites can be used as a highly effective adsorbents for the preconcentration and immobilization of radionuclides in environmental cleanup.