Selective Th(iv) capture from a new metal-organic framework with O^- groups

Area of Science:

• Materials Science
• Radiochemistry
• Environmental Chemistry

Background:

• Radioactive waste management poses significant challenges due to the toxicity of heavy metals like Thorium (Th(iv)).
• Developing selective adsorbents is crucial for efficient separation and capture of hazardous radionuclides from contaminated environments.
• Metal-organic frameworks (MOFs) offer tunable structures and high surface areas, making them promising candidates for adsorption applications.

Purpose of the Study:

• To synthesize and characterize a new 4-fold interpenetrated metal-organic framework (MOF) functionalized with O- groups.
• To evaluate the MOF's capacity and selectivity for capturing Thorium (Th(iv)) ions from aqueous solutions.
• To investigate the separation efficiency of Th(iv) from other metal ions with varying valence states.

Main Methods:

• Synthesis of a novel 4-fold interpenetrated MOF (compound 1a) featuring O- functional groups.
• Adsorption experiments to determine Th(iv) adsorption capacity, removal efficiency, and kinetics.
• Calculation of separation coefficients (S) for Th(iv) against various metal ions (La(iii), Sm(iii), Ho(iii), Cd(ii), K(i), Pb(ii)).
• Characterization of the adsorption process using FT-IR, SEM-EDS, and XPS techniques.

Main Results:

• The activated MOF (1a) exhibited a high adsorption capacity for Th(iv) (K_d = 3.16 × 10⁵ mL g^-1, 165.61 mg g^-1).
• Achieved >99.75% Th(iv) removal efficiency within 10 minutes from a 100 mg L^-1 solution, following pseudo-second-order kinetics.
• Demonstrated excellent selectivity for Th(iv) over various metal ions, with high separation coefficients (e.g., S_Th(IV)/K(I) = 255.79).
• Showed significant, albeit lower, selectivity for Th(iv) over Pb(ii) (S_{Th(IV)/Pb(II)} = 4.36), despite O- groups' known affinity for Pb(ii).

Conclusions:

• The developed O- functionalized MOF (1a) is a highly effective and selective adsorbent for Th(iv) capture.
• The material's rapid adsorption kinetics and high capacity make it suitable for practical applications in radioactive waste treatment.
• The MOF's performance highlights its potential for separating hazardous radionuclides from complex mixtures.