Two multifunctional Cu(ii) coordination complexes with mixed ligands as efficient catalysts for the oxygen evolution reaction and photocatalytic degradation of methyl orange azo dyes

Abstract

In order to solve the problems of environmental pollution and energy crisis, it is of great significance to develop low-cost, high-efficiency and environmentally friendly multifunctional materials to deal with environmental and energy concerns. Herein, two multifunctional Cu(II) coordination complexes with the formula {[Cu(m-bix)(FDC)(H₂O)]·H₂O}_n (1) and {[Cu₂(DAP)₄(NIP)₂]·DMF}_n (2) (m-bix = m-bis(imidazol-1-ylmethyl)benzene; DAP = N-(4-pyridyl)dimethylamine; H₂FDC = 2,5-furandicarboxylic acid; H₂NIP = 5-nitroisophthalic acid) were successfully constructed by using mixed ligands via a solvothermal method. Structural analyses show that both complexes exhibit a 1D chain structure, extending into a 3D supramolecular network via abundant hydrogen bonding forces. Electrochemical oxygen evolution reaction (OER) catalytic studies reveal that 1 and 2 are efficient electrocatalysts for the OER. In particular, 2 has a lower overpotential of 360 mV at 1 mA cm⁻² under alkaline conditions. Furthermore, both complexes exhibit excellent photocatalytic activity due to their narrow band gaps – 2.51 eV (494 nm) for 1 and 2.77 eV (448 nm) for 2. The oxidation system composed of the complex and H₂O₂ can degrade methyl orange azo dyes (40 mg L⁻¹) to less than 10% in only 150 minutes under sunlight irradiation. This work demonstrates that employing mixed ligands is a promising approach to obtain multifunctional complexes. It also opens up a unique path for the development of high-efficiency, low-cost, and environmentally friendly multifunctional materials to address environmental and energy issues.