Fabrication of carboxyl and amino functionalized carbonaceous microspheres and their enhanced adsorption behaviors of U(VI)

Abstract

Design and fabrication of materials with abundant functional groups represent an important and promising direction in the remediation of aqueous contaminants. In recent years, carbon-based materials have drawn widespread concern on account of their low cost, large specific surface area, good chemical stability as well as controllable porosity. The U(VI) binding onto raw carbon-based materials is still confronted with the problem of limited adsorption capacity, which severely hinders the practical applications of materials. Herein, amino- and carboxyl-functionalized carbonaceous spheres (denoted as ACSs and CCSs) were fabricated by in-situ polymerization and simply annealing methods, respectively. The highest adsorption amounts of ACSs and CCSs towards U(VI) were calculated to be 73.83 and 401.61 mg·g−1 from Langmuir model at pH = 4.0 and 298 K, which were higher to that of raw carbonaceous material (19.31 mg·g−1). Interestingly, the Freundlich model could well simulate U(VI) sorption isotherms on ACSs at these temperatures (T = 298, 313 and 328 K), while U(VI) sorption isotherms on CCSs were able to significantly conform to the Langmuir model. According to FT-IR and XPS analysis, U(VI) was enriched on both materials on account of the ample functional groups on ACSs (e.g. CNOH/CNH2) and CCSs (e.g. OH/COOH). In addition, effect of ionic strength manifested that U(VI) elimination on ACSs and CCSs were greatly caused by the formation of outer-sphere and inner-sphere surface complexes, respectively. This work promises to provide two facile approaches for engineering diverse functionalized materials towards a highly rapid and efficient sequestering U(VI) from contaminated water.