Temperature-induced structural diversity of metal-organic frameworks and their applications in selective sensing of nitrobenzene and electrocatalyzing the oxygen evolution reaction.

ABSTRACT

Structural diversities are presented in four new Co-MOFs containing 1,5-bi(imidazolyl)anthracene and different dibenzobarrelene skeletons based on dicarboxylic acid, in which MOFs 1-3 exhibit 2D networks in a 4-connected node sql topology with the point symbol of {44·62}, while MOF 4 forms a 1D chain structure. It is clearly observed that the 2D-1D structural transformation of 2-4 has been realized by temperature modulated hydrothermal synthesis procedures from 120-160 °C, suggesting the key role of temperature for constructing MOFs. In addition, obvious π-π interactions between anthracene rings can be observed in the architectures of 1-3, which may favorably stabilize their 2D supramolecular networks. More importantly, fluorescence behaviors of 1-4 have been investigated in water among various nitro-aromatic compounds (NACs) and the results show that all samples exhibit high selectivity and fine sensitivity to nitrobenzene (NB) with fluorescence quenching, which is confirmed to be the result of electron transfer from the excited state of ligands to that of NB by density functional theory. Furthermore, MOFs 1-4 have been directly employed as electrocatalysts for the oxygen evolution reaction (OER), in which MOF 4 gives the best activity towards the OER among all as-synthesized samples with an overpotential of 398 mV at a current density of 10 mA cm-2 and a low Tafel slope of 59 mV dec-1.