Preparation of porous chitosan/carboxylated carbon nanotube composite aerogels for the efficient removal of uranium(VI) from aqueous solution

The porous chitosan/carboxylated carbon nanotubes composite aerogels (CS-CCN) with different CCN contents were prepared for the efficient removal of U(VI) from aqueous solution. The successful formation of CS-CCN aerogels with highly porous structure was confirmed by different characterizations (such as SEM, TEM, XRD, etc.). The sorption capacity of the aerogels depends on CCN content, which has significant impact on the porous structure and the sorption ability of the aerogels. The CS-CCN aerogels were found to be very effective for U(VI) sorption: the maximummono-layer sorption capacity for CS-CCN2 aerogel reached 307.5 mg/g at pH 5.0 and 298 K. The chemisorption or surface complexation through sharing of O/N lone pair electrons on the active sites (carboxylic and amine groups) was responsible for U(VI) sorption, which is confirmed by the IR and XPS analysis. Meanwhile, the good-fitting of both sorption kinetics by pseudo-second-order model and sorption isotherms by Langmuir model also indicates chemisorption mechanism. The thermodynamic data suggest that U(VI) sorption on CS-CCN aerogel is endothermic and spontaneous. The unique characteristics such as high sorption capacity, fast kinetic, and easy recovery from solution make CS-CCN aerogels be very efficient sorbents for the treatment of radioactive wastewater. (C) 2020 Published by Elsevier B.V.