Introduction of benzotriazole into graphene oxide for highly selective coadsorption of An and Ln: Facile synthesis and theoretical study

The removal of actinide (An) and lanthanide (Ln) elements from aqueous solution is a significant strategy for the safe disposal of radioactive wastes. Herein we presented a 5-methylbenzotriazole modified graphene oxide (MBTA-GO) as a novel adsorbent, in which benzotriazole group was used as targeted sorption site bearing strong affinity toward An-Ln (An and Ln) ions for the first time. MBTA-GO was characterized by Fourier transformed infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The effect of pH and initial concentration on combined adsorption of An-Ln were examined, and the results showed that the adsorption of metal ions on MBTA-GO was strongly dependent on pH in multi-cation solution, and MBTA-GO exhibited excellent An-Ln selectivity (selectivity coefficients are more than 99%), overwhelming majority of other reported adsorbents. The cycle experiments revealed that the MBTA-GO exhibited good reusability and structural stability. By density functional theory (DFT) calculation, the binding energy of Cation-MBTA-GO followed the order of Th(IV) > U(VI) > Eu(III) > La(III) > Sr(II) > Cs(I), suggesting that the benzotriazole groups were preferentially responsible for An-Ln ions on MBTA-GO, which is in well agreement with the experimental results. Finally, the mechanism of selective coadsorption was revealed, which is the synergistic effect of chemical complexation and electrostatic interaction.