3D construction of a cobalt(ii) coordination polymer as a photocatalyst for the degradation of methyl green dye under visible light and its mechanistic pathway

Abstract

A new cobalt(II) coordination polymer ‘Cp-Co’ has been designed and synthesized. The construction includes cobalt(II) as the central metal core along with 1,4-benzenedicarboxylic acid and the spacer 3,5-diamino-1,2,4-triazole obtained by a solvothermal method. The architecture of ‘Cp-Co’ was established using single X-ray crystallography and the topology of the coordination polymer. The ‘Cp-Co’ exhibited a periodic 3D framework. Furthermore, infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) analysis further supported the structure of ‘Cp-Co’. The prepared material was explored as a catalyst for the photocatalytic degradation of methyl green (MG) dye and displayed outstanding degradation efficiency under visible light radiation. The experimental design was explored towards optimization of the reaction variables, such as catalyst dose, MG dye concentration, etc. It was found that 10 mg of Cp-Co with 150 mg L⁻¹ MG resulted in 99.77% photocatalytic efficiency within 60 min of visible light irradiation. The kinetic data was simulated using the Langmuir–Hinshelwood kinetic model and the value of the apparent rate constant (Kapp) was found to be 0.020 min⁻¹, 0.024 min⁻¹ and 0.029 min⁻¹ for 50, 100 and 150 mg L⁻¹ MG concentrations. The trapping experiments suggested the involvement of a superoxide anion radical (O₂⁻˙) in the degradation of MG.