Post-synthetic modification of CAU-10-pydc nanosheets with sulfonic acid groups: A robust MOF-based heterogeneous acid catalyst for efficient oleic acid esterification

Abstract

A special class of aluminum-based metal-organic frameworks (MOFs) named as CAU-10-pydc with a unique nanosheet morphology was used for the first time as a solid support to prepare an efficient and novel heterogeneous acid catalyst. This MOF was facilely synthesized through a conventional solvothermal technique, and sulfonic acid groups were post-synthetically introduced to the CAU-10-pydc framework via the nucleophilic interaction of pyridinic N atoms of organic ligand with 1,3-propanesultone and subsequent treatment with sulfuric acid. The successful incorporation of sulfonic acid groups in CAU-10-pydc structure was confirmed using FT-IR, EDX-map, XPS, and N₂-sorption analyses, while the modification potential of this MOF was precisely determined using ¹H NMR technique. Also, this kind of MOF was found structurally stable during the post-synthetic modification (PSM) process, which was evaluated by XRD and FE-SEM techniques. The catalytic performance of as-prepared CAU-10-pydc/PrSO₃H catalyst was evaluated in acid-catalyzed esterification of oleic acid with methanol to produce renewable, ecofriendly, and sulfur-free biodiesel. The high oleic acid conversion of 95.5 % was achieved with sustained combustibility following a short reaction time of 2 h in the presence of CAU-10-pydc/PrSO₃H catalyst, while the non-catalytic experiment and unfunctionalized CAU-10-pydc exhibited much lower catalytic activity.