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Selective Adsorption of Rare Earth Elements over Functionalized Cr-MIL-101
Summary:
The authors from Department of Chemistry and Chemical Engineering, Inha University (Republic of Korea) developed functionalized Cr-MIL-101 MOFs with high stability and selectivity, achieving excellent rare earth elements (REEs) adsorption performance in aqueous solution separation.
Background:
1. To address the growing demand for REEs and defects of traditional separation methods (high cost, pollution, low efficiency), previous researchers used MOFs as adsorbents but suffered from low adsorption capacity and sluggish kinetics.
2. The authors proposed synthesizing Cr-MIL-101 and its derivatives via direct/postsynthetic modification, introducing diverse functional groups to enhance REE adsorption capacity and selectivity.
Research Content:
1.Synthesis: Prepared MIL-101, MIL-101-NH₂, MIL-101-ED, MIL-101-DETA, and MIL-101-PMIDA using ligands like H₂BDC, H₂BDC-NH₂, and PMIDA, via mixing, heating, refluxing, filtration, and drying.
2.Characterizations:
1) BET surface area: MIL-101 (3680 m²/g), MIL-101-PMIDA (989 m²/g); pore volume: MIL-101 (2.01 cm³/g), MIL-101-PMIDA (0.65 cm³/g); average pore diameter 1.2-2.31 nm.
2) SEM tests show octahedral morphology; MIL-101-NH₂ and MIL-101-PMIDA particle size ~0.5 μm, others ~1 μm.
3) FT-IR detected functional group peaks; zeta potential negative at pH>3, increasing with pH.
3.Application: Adsorbed La³⁺, Ce³⁺, Nd³⁺, Sm³⁺, Gd³⁺; MIL-101-PMIDA had maximum Gd³⁺ adsorption capacity (90.0 mg/g, pH=5.5), selectivity ~90% against transition metals, stable for 5 cycles.
4.Mechanism: High pH promotes deprotonation of functional groups, realizing REE adsorption via surface complexation (COO⁻, PO₃²⁻, -NH₂ with Gd³⁺) and electrostatic attraction (-NH₂-OH⁻ with Gd³⁺); chemisorption is rate-limiting (pseudo-second-order model).
Outlook:
This research develops high-performance functionalized MOF adsorbents, providing an efficient, green solution for REE separation, with significant industrial application value.
Selective Adsorption of Rare Earth Elements over Functionalized Cr-MIL-101
Authors: Yu-Ri Lee, Kwangsun Yu, Seenu Ravi, Wha-Seung Ahn*
DOI: 10.1021/acsami.8b07130
Link: https://pubs.acs.org/doi/10.1021/acsami.8b07130
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