Superior immobilization of U(VI) and 243Am(III) on polyethyleneimine modified lamellar carbon nitride composite from water environment

A novel low-cost, effective and environmental-friendly laminated carbon nitride decorated with polydopamine (PDA) and grafted with polyethyleneimine (PEI) brush (l-C3N4/PDA/PEI3) was successfully synthesized and applied as environmental cleaner for removing U(VI) ions from aqueous solutions under various environmental conditions. The adsorption isotherms fitted well by the Langmuir model, suggesting that the removal of U(VI) on l-C3N4/PDA/PEI3 was monolayer coverage. The effects of different PEI contents were also investigated and the results demonstrated that the adsorption capacity of U(VI) on l-C3N4/PDA/PEIx decreased at higher content of PEI. Typically, various cations (Ca2+ and Mg2+) and SO42− could inhibit the adsorption through competitive coordination with U(VI), while CO32− promoted U(VI) sorption owing to the formation of indissolvable complexes. The main driving force between U(VI) and l-C3N4/PDA/PEI3 was surface complexation with various functional groups (CC, CO, NCC, and CC or CH) and electrostatic attraction. According to the analysis of EXAFS spectra, the occurrence of U-C and U-U shell revealed that inner-sphere complexation and surface co-precipitation dominated the adsorption of U(VI) on l-C3N4/PDA/PEI3 at pH 5.0. The composites were also applied to remove 243Am(III), Cu(II) and Pb(II) ions at different pH values, and similar results were also found for these metal ions. Such a facile synthesis method and efficient removal performance suggested that the l-C3N4/PDA/PEI3 materials might be a promising adsorbent for efficient elimination of radionuclides and heavy metal ions in environmental pollution management.