The role of supramolecular interactions and pyridine groups in the (photo)electrocatalytic properties of a non-precious Co-based MOF

Abstract

The influence of functional group coordination on the (photo)electrocatalytic (PEC) properties of two cobalt-based MOFs is studied in this work. Different synthesis temperatures during the solvothermal method produce two polymorphic MOFs. Co-MOF1 (120 °C) presents a nitrogen-to-cobalt coordination bond; meanwhile, Co-MOF2 (90 °C) shows a non-coordinated free amine group. Co-MOF1 exhibits a better crystallization, with a higher crystallite size, and smaller particles, thus inducing a higher surface area. Both materials present similar UV-vis spectra, indicating the same electronic transitions; nevertheless, Co-MOF2 presents a lower bandgap related to the free amine in the 5-aminoisophthalate linker. Computational analysis shows that the 4,4′-bipyridyl linkers in Co-MOF2 present higher electronic density than in Co-MOF1, as these are responsible for decreasing the HOMO energy of Co-MOF2. Regarding PEC characterization, Co-MOF2 presents better light-harvesting promoted by a narrower bandgap; meanwhile, Co-MOF1 exhibits better charge transport properties and higher stability, attributed to higher crystallinity. Both materials present an n-type photocatalytic response. Physicochemical measurements indicate that the coordination of functional groups is a useful parameter to control the electronic density of linkers, thus decreasing the HOMO energy and generating lower energetic bandgaps. The correlation between structural, morphological, optical, and catalytic properties, and supramolecular interactions suggests that Co-MOF2 presents an enhanced PEC activity; however, it also displays instability issues. Conversely, Co-MOF1 offers higher stability but a lower PEC response. Such characteristics could be taken advantage of, depending on the specific application. In this way, both MOFs are promising materials to perform advanced (photo)electrocatalytic oxidation processes.