Efficient Removal of Uranium(VI) from Aqueous Solutions by Triethylenetetramine-Functionalized Single-Walled Carbon Nanohorns

In the present study, SWCNH-COOH and SWCNH-TETA were fabricated using single-walled carbon nanohorns (SWCNHs) via carboxylation and grafting with triethylenetetramine (TETA) for uranium (VI) ion [U(VI)] removal. The morpho-structural characterization of as-prepared adsorbing materials was performed by transmission electron microscopy, X-ray diffractometry, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Several parameters including the pH value of the aqueous solutions, contact time, temperature, and U(VI) concentration were used to evaluate the sorption efficiency of SWCNH-COOH and SWCNH-TETA. The Langmuir isotherm model could well represent the as-obtained adsorption isotherms, and the kinetics was successfully modeled by pseudo-second-order kinetics in the adsorption process. The maximum adsorption capacity of SWCNH-TETA was calculated as 333.13 mg/g considering the Langmuir isotherm model. Thermodynamic studies showed that adsorption proved to be a spontaneous endothermic process. Moreover, SWCNH-TETA exhibited excellent recycling performance and selective adsorption of uranium. Furthermore, the possible mechanism was investigated by XPS and density functional theory calculations, indicating that the excellent adsorption was attributed to the cooperation capability between uranium ions and nitrogen atoms in SWCNH-TETA. This efficient approach can provide a strategy for developing high-performance adsorbents for U(VI) removal from wastewater.