Development of cysteine amide reduced graphene oxide (CARGO) nano-adsorbents for enhanced uranyl ions removal from aqueous medium

The affinity of uranyl ions for binding with nitrogen bearing ligands has led to development of several amine/amide reduced graphene oxides as adsorbent for uranyl ion removal. We have developed a novel nano-adsorbent (referred as CARGO) with an aim of increasing nitrogen groups in reduced graphene oxide (GO) for enhanced uranyl ion removal. There are two important stages in this work: (a) synthesis of CARGO, which comprises of GO reduction by the as synthesized L-cysteine amide and (b) optimization of uranyl ion adsorption by CARGO. The synthesis of L-cysteine amide (precursor) is confirmed by FT-IR and H-1 NMR. Reduction of GO by L-cysteine amide is revealed from decrease in the acidic functionalities of GO and characterized by XRD, UV-vis, Raman and FT-IR spectroscopy techniques. The FE-SEM and TEM studies CARGO revealed flake like morphology. The uranyl ion adsorption on CARGO surface was confirmed from EDX analysis and supported by two dimensional elemental maps of uranium and carbon. The regeneration, re-usability and selectivity of uranium adsorption by CARGO have been studied. The uranyl adsorption was kinetically and thermodynamically favorable, which accounted for 88.9% uranyl ion removal in 60 min at an optimized pH 5 via chemisorption mechanism and the corresponding q (max) derived from Langmuir adsorption isotherm was 337.93 mg/g. Such high uranyl ion adsorption capacity is attributed to more amine and/or amide binding sites on CARGO, high BET surface area (57.086 m(2)/g) and negative zeta potential values of the adsorbent.