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.