Photocatalytic degradation of methylene blue dye and electrocatalytic water oxidation over copper(II) complex with mixed ligands

In this study, the preparation of copper(II) complex formulated, [Cu(3-nitrobenzoic acid)₂(1-Me-imi)₂] (1), (where 1-Me-imi is 1-Methylimidazole) were done by using Cu(NO₃)₂·3H₂O, 1-methylimidazole and 3-nitrobenzoic acid in mixed solvents (MeOH/H₂O). This complex was characterized by FTIR, elemental analysis, and single X-ray crystallography. The crystal structure shows two isostructural units with different bond lengths and angles. Its geometry can be described as a distorted octahedron with six coordination numbers. The photocatalytic activity of (1) was studied against methylene blue (MB) dye in aqueous media under UV light irradiation. The reaction parameters influencing photocatalytic activity were optimized. Photocatalytic activity of 70.71% was attained under optimized conditions (initial dye concentration = 40 mg/L, catalyst dosage = 0.5 g, pH = 10, temperature = 333 K, and irradiation time = 40 min). The recyclability test indicated good catalyst stability without losing photocatalytic activity even after four consecutive catalytic runs. Furthermore, pseudo-first-order kinetics was assumed for the photocatalytic reaction with a high-rate constant of 0.02368 min⁻¹. The scavenging study investigated that among various reactive species involved in the photocatalytic reaction, hydroxyl radicals (OH•) have the prominent contribution followed by superoxide anion (∙O₂^-) and positive holes (h⁺). In electrochemical studies for oxygen evolution reaction (OER), 1 has a low overpotential with a Tafel slope 91 mVdec^-1. Electrochemical impedance spectroscopy measurements indicate a small RCT value of 1.178 Ω and the complex was found stable by Chronoamperometric analysis. Magnetic study measurements indicate about no long-range antiferromagnetic interaction in 1.