Acrylic Acid-Functionalized Metal–Organic Frameworks for Sc(III) Selective Adsorption

The increasing demand for rare-earth elements (REEs) due to their extensive high-tech applications has encouraged the development of new sustainable approaches for REE recovery and separation. In this work, a series of acrylic acid-functionalized metal–organic framework materials (named as y-AA-x@MIL-101s) were prepared and used for selective adsorption of Sc­(III). The adsorbent was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, nitrogen adsorption, X-ray photoelectron spectroscopy, and zeta potential and surface functional-group titration. The adsorption isotherm and kinetics data were accurately described by the Langmuir and pseudo-second-order models. The adsorption capacity of the material for Sc­(III), Nd­(III), Gd­(III), and Er­(III) was 90.21, 104.59, 58.29, and 74.94 mg g^–1, respectively. Importantly, the adsorbent was better for selective recovery of Sc­(III) not only from the 16 REE mixed system but also the Cu­(II), Zn­(II), Mn­(II), Co­(II), and Al­(III) coexistence solution. Except for Sc­(III), the material displayed high affinity for Nd­(III) in the light rare-earth mixture and for Gd­(III) in the middle rare-earth mixture. All in all, this study provides a new method for separation and recovery of REEs, which makes this work highly significant in separation and enrichment.