Sulfolane as a Solvent for Nano-MOF Synthesis: Enabling Prolonged Nucleation and Controlled Growth

Conventional methods for synthesizing nano-sized metal-organic frameworks (nano-MOFs) often rely on additives or extra conditions, overlooking the critical role of solvents. Here, we highlight tetramethylene sulfone (TMS, or sulfolane) as a versatile solvent for nano-MOF synthesis. TMS forms strong solvation structures with metal ions and inhibits ligand deprotonation, enabling control over particle size. Using TMS, we synthesized ZIF-65 [Zn(2-nIm)₂, 2-nIm = 2-nitroimidazole], ZIF-8 [Zn(2-mIm)₂, 2-mIm = 2-methylimidazole], UiO-66 [Zr₆O₄(OH)₄(BDC)₆, BDC = 1,4-dicarboxybenzene acid], and MOF-199 [Cu₃(BTC)₂, BTC = 1,3,5-benzenetricarboxylic acid] with significantly smaller particle sizes compared to traditional solvents like ethanol (EtOH). Systematic analysis on the growth of ZIF-65 revealed distinct growth behaviors: in TMS, slower kinetics allowed the coexistence of nucleation and growth over an extended period, leading to an increase in particle number while maintaining relatively constant size; in contrast, EtOH promoted rapid growth followed by Ostwald ripening, resulting in larger particles and reduced particle number over time. By adjusting reactant concentration, metal-to-ligand ratio, and reaction temperature, we achieved facile size modulation of ZIF-65 nanoparticles. This work underscores the importance of solvents in nano-MOF synthesis and offers a robust strategy for tailoring MOF particle size, advancing applications in catalysis, biomedicine, and beyond.