Sulfur-Functionalized MOF via Ligand Additive-Stabilized SALE for Efficient Hg²⁺ Ion Removal

Area of Science:

• Materials Science
• Environmental Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are crucial for adsorption and separation.
• Post-synthetic modification, like solvent-assisted linker exchange (SALE), allows precise functionalization.
• Incorporating linkers with Lewis basic sites into MOFs can destabilize the framework.

Purpose of the Study:

• To develop a stable method for functionalizing zeolitic imidazolate framework-8 (ZIF-8) with sulfur-containing linkers.
• To investigate the impact of SALE parameters on MOF stability and functionalization efficiency.
• To evaluate the performance of sulfur-functionalized ZIF-8 for mercury ion (Hg²⁺) removal.

Main Methods:

• Ligand additive-stabilized solvent-assisted linker exchange (SALE) was employed to incorporate 2-mercaptoimidazole into ZIF-8.
• Systematic variation of SALE parameters (ligand concentration, time, solvent) was performed.
• Quantitative image analysis was used to study MOF morphology and structural transformations.

Main Results:

• The ligand additive-stabilized SALE successfully preserved ZIF-8 crystallinity and porosity.
• Sulfur-functionalized ZIF-8 demonstrated a high Hg²⁺ adsorption capacity (1504 mg g^-1).
• The material exhibited excellent recyclability (>95% capacity retention over cycles) and broad pH applicability for Hg²⁺ removal.

Conclusions:

• Ligand additive-stabilized SALE is a robust method for introducing sulfur functionalities into MOFs.
• Sulfur-functionalized ZIF-8 shows significant potential for efficient and practical mercury remediation.
• This approach opens new avenues for designing functional MOFs for environmental applications.