Ionic-liquid-functionalized metal-organic frameworks are attractive platforms for oxyanion capture, but their practical performance is often compromised by severe pore blockage, insufficient accessibility of exchange sites, and limited interfacial stability under aqueous or acidic conditions. This work presents a thermally reconstructed ionic-liquid@MIL-101-NH₂ hybrid adsorbent for ReO₄^- capture. EMIMBr was introduced into MIL-101-NH₂, followed by thermal treatment under N₂ to generate a series of HTIL@MOF composites with different IL/MOF mass ratios.
Structural characterization shows that direct ionic-liquid incorporation causes extensive pore occupation, whereas thermal treatment partially restores pore accessibility and redistributes the ionic liquid within the framework. The BET surface area, pore volume, and micropore volume of HTIL@MOF increase progressively from 1:1 to 4:1, indicating that thermal reconstruction generates a more accessible pore network at moderate IL loadings. At a higher IL/MOF mass ratio of 6:1, the surface area decreases again, suggesting renewed pore occupation by excess ionic liquid. Nevertheless, HTIL@MOF (6:1) exhibits the highest ReO₄^- uptake, demonstrating that adsorption performance is governed not by surface area alone but by the balance between pore accessibility and ionic-liquid-derived exchange-site density.
FTIR, XPS, TGA, DFT calculations, electron microscopy, and post-adsorption analyses collectively support the formation of a thermally reconstructed IL/MOF interface with altered local coordination and electronic environments. Theoretical calculations further reveal the formation of defect-associated coordination environments. ReO₄^- is preferentially stabilized at the coupled MOF-IL interface, with a calculated adsorption energy of −1.60 eV, indicating thermodynamically favorable perrhenate binding at the reconstructed interfacial region. Charge-density-difference and electrostatic-potential analyses reveal interfacial charge redistribution and positively polarized domains that promote oxyanion enrichment.
Adsorption experiments demonstrate that HTIL@MOF (6:1) achieves a maximum ReO₄^- uptake of 242.74 mg g^-1 (a 6.05-fold enhancement over pristine MIL-101-NH₂), with equilibrium attained within 20 min. Kinetic analysis reveals that the Elovich model (R² = 0.959) provides the best fit, and isotherm modeling shows that the Sips model outperform the Langmuir and Freundlich models, with a Sips-derived maximum capacity of 522.29 mg g^-1 at 45 °C, collectively confirming heterogeneous multi-site adsorption at the reconstructed interface. The composite maintains 64.72% removal efficiency in 3 mol L^-1 HNO₃ at a solid-to-liquid ratio of 100 g L^-1, retains selectivity toward ReO₄^- in the presence of competing anions (Cl^-, NO₃^-, ClO₃^-, SO₄^2-), and exhibits stable performance over eight adsorption–desorption cycles. The improved performance is attributed to the synergistic effects of restored pore accessibility, ionic-liquid-mediated ion exchange, interfacial polarization, and favorable ReO₄^- binding at the reconstructed MOF-IL interface. This work provides a thermally assisted interfacial reconstruction strategy for designing robust IL/MOF hybrid adsorbents for perrhenate/pertechnetate-related oxyanion separations.
 

MIL-101-NH2; ionic liquid; thermally reconstructed interface; perrhenate adsorption; ion exchange; metal-organic framework