Interactions between Th(IV) and graphene oxide: experimental and density functional theoretical investigations

Graphene oxide (GO) has been receiving increasing research efforts in recent years because of its wide applications in various scientific fields. In this work the sorption of Th(IV) onto graphene oxide (GO) was studied using a batch method under ambient conditions. The sorption kinetics were found to be fast and fitted the pseudo-second-order model very well, with an equilibrium time of about 10 min. The sorption is strongly dependent on the solution pH but independent of the ionic strength of the solution. The maximum sorption capacity of as high as 214.6 mg g(-1) can be achieved at pH 2.60 +/- 0.05, and Th(IV) can be desorbed readily from the GO with 1.0 M HNO3. The thermodynamic investigations revealed that the sorption of Th(IV) on the GO was an endothermic and spontaneous process. The Scanning Electron Microscopy (SEM) results indicated obvious surface morphology changes of the GO induced by Th(IV) sorption. Furthermore, the interaction mechanism of Th(IV) and the GO was investigated by infrared (IR) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy combined with density functional theory (DFT) calculations. The results of EXAFS indicated that Th(IV) was bonded to similar to 8 or 9 oxygen atoms and the average bond length of Th-O was estimated to be similar to 2.45 angstrom in the first coordination shell. The DFT calculations further confirm the rationality of experimental and the EXAFS results. This work demonstrates the tremendous potential opportunities offered by GO in preconcentration and removal of thorium and other tetravalent actinides for the recovery and remediation of the environment.