Enhancing Esterification Efficiency via Post-Synthetic Acid Modification of Co- and Zn-Based MOFs

Abstract

Post-synthetic modification (PSM) has emerged as a strategic route to tailor the functionality of metal–organic frameworks (MOFs) for diverse applications, particularly in catalysis. This study explores the structural and catalytic enhancement of cobalt- and zinc-based MOFs via acid-functionalization using H₂SO₄ and H₃PO₄. The acid-modified MOFs were characterized using XRD, FTIR, SEM–EDX, and NMR analyses to confirm structural integrity, functional group incorporation, and morphological changes. XRD revealed preserved crystallinity post treatment, while FTIR confirmed the successful grafting of acidic functionalities. SEM micrographs showed increased surface roughness and porosity, with EDX confirming elemental changes linked to acid uptake. Catalytic evaluation was conducted through esterification of model carboxylic acids with alcohols. The acid functionalized MOFs demonstrated a significant improvement in catalytic efficiency compared to unmodified counterparts, with yields reaching up to 88% for Co-MOF-H₃PO₄ and 85% for Zn-MOF-H₂SO₄. Enhanced yields were attributed to increased Brønsted acidity and improved active site accessibility. A correlation was observed between acid strength, structural modification, and catalytic performance. This work provides a comparative insight into the effects of H₂SO₄ and H₃PO₄ treatments, revealing the superior performance of phosphoric acid in certain cases due to its mild yet effective modification profile. The findings underscore the potential of PSM in advancing MOF-based catalysis for sustainable and efficient ester synthesis.