▎ 摘　　要

The sorption mechanism of Th(IV) on amidoxime/graphene oxide composites was investigated by extended X-ray absorption fine structure (EXAFS) spectra and surface complexation modeling. It was found that amidoxime/graphene oxide composites possessed a variety of oxygen-and nitrogen-containing functional groups such as hydroxyl, carboxyl, carbonyl, amine and imine groups. The sorption kinetics and sorption isotherms of Th(IV) on amidoxime/graphene oxide composites can be satisfactorily fitted by the pseudo-second- order kinetic model and the Langmuir model, respectively. The maximum sorption capacity of Th(IV) on amidoxime/graphene oxide composites calculated from the Langmuir model at pH 2.0 and 293 K was 123.46 mg g(-1). According to EXAFS analysis, the presence of a Th-C shell (R = 2.97 angstrom, CN = 4.9) indicated that inner-sphere surface complexation dominated the sorption of Th(IV) on amidoxime/graphene oxide composites at pH 2.0, whereas the occurrence of a Th-Th shell revealed that a surface precipitate dominated the sorption of Th(IV) on amidoxime/graphene oxide composites at pH 5.0. The pH-dependent sorption behaviors of Th(IV) on amidoxime/graphene oxide composites can be satisfactorily simulated by double layer modeling based on two inner-sphere surface complexes and a surface precipitate. These observations revealed that the amidoxime/graphene oxide composites can be regarded as a promising adsorbent to remove tetravalent radionuclides from aqueous solutions in environmental cleanup.