High-performance scavenging of Nd (III) and Sm (III) from water by a copper-based metal-organic framework HKUST-1

The increasing demand for neodymium (III) and samarium (III) due to their extensive high-tech applications has drawn much attention to their recovery. In this work, the copper-based metal-organic framework HKUST-1 was prepared and used for the adsorption of neodymium (III) and samarium (III) in the media of an aqueous solution. The maximum adsorption capacity of the material for neodymium (III) and samarium (III) was 284.11 and 503.45 mg g⁻¹ at a pH of 5.5, respectively. The adsorption removal rate could achieve nearly 100% at the solid-to-liquid ratio of 1.0 g L⁻¹, which is relatively excellent among such adsorbents used for rare earth elements uptake. The mechanism and reversibility of neodymium (III) and samarium (III) adsorption were systematically investigated by X-ray diffraction, Fourier transforms infrared spectroscopy, Raman spectra, and X-ray photoelectron spectroscopy, suggesting that the mechanism for the adsorption was ion exchange and complexation between trivalent rare-earth ions and the oxygen atom in the hydroxyl group. The reason behind the material displaying a more robust affinity for samarium (III) may be caused by the energy difference between fⁿ and fⁿ⁺¹ states of samarium (III) was larger than that of neodymium (III), thus forming stronger covalent bonding.

Graphical abstract

HKUST-1 exhibited high adsorption capacity towards Nd (III) and Sm (III). The reason behind the material displaying a more robust affinity for Sm(III) was caused by that the energy difference between fⁿ and fⁿ⁺¹ states of Sm(III) was larger than that of Nd(III), thus forming stronger covalent bonding.