The adsorption of U(VI) on carbonaceous nanofibers: A combined batch, EXAFS and modeling techniques

The adsorption mechanism between U(VI) and carbonaceous nanofibers (CNFs) was demonstrated by batch, EXAFS and surface complexation modeling. The batch experiments indicated that the adsorption of U(VI) on CNFs decreased with increasing ionic strength at pH < 4.0, whereas the U(VI) adsorption was independent of ionic strength at pH 4.0-7.0. The adsorption kinetics and isotherms of U(VI) adsorption can be satisfactorily fitted by pseudo-second-order kinetic model and Langmuir model, respectively. The maximum adsorption capacity of CNFs for U(VI) calculated from Langmuir model at pH 4.5 and 293 K was 52.63 mg/g. The results of EXAFS analysis revealed that the adsorption mechanism of U(VI) on the CNFs at pH 4.0 was outer-sphere surface complexation, whereas inner-sphere surface complexation/surface co-precipitate dominated the adsorption mechanism of U(VI) on the CNFs at pH 7.0. The adsorption of U(VI) on CNFs can be fitted by double diffuse layer modeling with an outer-sphere surface complexes (SOHUO22+ species) and an inner-sphere surface complexes (SOUO2+ species) very well. The findings presented herein showed that CNFs can be regarded as a promising candidate for the preconcentration and immobilization of radionuclides from aqueous solutions in environmental remediation.