Ligand-engineered zeolite imidazole frameworks for environmental and energy applications

Abstract

Zeolitic imidazolate frameworks (ZIFs), a subset of metal-organic frameworks (MOFs), exhibit high crystallinity, tunable porosity, large surface areas, and excellent chemical stability, making them promise for environmental and energy applications. However, challenges such as limited mesoscale cavities, saturated metal sites, poor stability in catalytic environments, and low conductivity hinder their broader utility. This thesis focuses on ligand engineering strategies for ZIF frameworks (ZIF-8 and ZIF-67) with sodalite topologies to address these issues.In the first project, I employed the selective ligand removal (SeLiRe) strategy to fabricate hierarchically porous ZIFs with dual-pore structures, achieving a 40-fold enhancement in dye adsorption capacity due to increased pore volume and rapid molecular diffusion. The second project explored the introduction of open metal sites (OMS) within ZIF frameworks. By utilizing in-situ spectroscopy and electrochemical methods, unsaturated Zn−N2 sites were found to chemisorb hydroxide ions, forming high-valence HO−Zn−N2 active sites, resulting in efficient hydrogen evolution reaction (HER) performance with remarkable stability.In the third project, I synthesized mixed-ligand ZIF-67 variants to investigate their (photo)electrocatalytic oxygen evolution reaction (OER) properties. Specific secondary ligands promoted the in-situ formation of cobalt (oxy)hydroxide layers, improving conductivity and stability. The synergistic interface enhanced catalytic efficiency and durability, underscoring the potential of ligand engineering to develop advanced frameworks for sustainable applications. These results indicate that the ligand engineering strategy is a powerful tool to design advanced functional frameworks with enhanced activity, selectivity and durability in environmental and energy applications.