Amidoxime modified chitosan/graphene oxide composite for efficient adsorption of U(VI) from aqueous solutions

Graphene oxide (GO) and its composites are promising candidates for the adsorption of U(VI) in water. Whereas the high hydrophobicity and dispersibility of GO makes it hard to separate from aqueous solutions, and thus greatly restricts its practical application. To address this defect, a novel composite [i.e., poly(amidoxime)/GO/chitosan (PAO/GO/CS)] was prepared. Characterization including Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed that cross-linking reaction between GO and CS may consume oxygen-contained groups of GO. The resulting deficit in U(VI) adsorption may be compensated by the amidoxime grafted onto the surface of GO/CS. Langmuir model showed that the maximum adsorption capacity of U(VI) by PAO/GO/CS was up to 701.5, 821.7, and 1220.0 mg/g, respectively, under 293, 303, and 313 K at pH 6.0. U(VI) is spontaneously and mainly chemically adsorbed onto the oxygen-containing groups (i.e., hydroxyl and amidoxime) in PAO/GO/CS based on characterization and density functional theory (DFT). DFT analysis indicated that the optimized adsorption energy of most stable configuration of the uranyl-PAO/GO/CS is −309.99 kcal/mol. PAO/GO/CS can achieve selective adsorption for U(VI) against common coexisting ions and superior separation from water. These findings demonstrate the feasibility of PAO/GO/CS composite used for the remediation of uranium-containing wastewater.