Synthesis, crystal structure, photocatalytic properties and Hirshfeld surface analysis of Co(II)-based complex: An environmental approach for degradation of organic dyes

Abstract

A new mixed-ligand Co(II) complex, formulated as: [Co(1-methylimidazole)4(H2O)2].(pic)2, (1) (where pic = picrate) has been successfully synthesized using 1-methylimidazole and picric acid in mixed solvents (CH3OH and H2O). The characterization of (1) was carried out through various techniques such as FTIR, elemental analysis, and single X-ray crystallography. The X-ray study indicates that the Co(II) exhibits six coordination numbers with distorted octahedral geometry. Further, the supramolecular structure of 1 demonstrates the bifurcated hydrogen bonding between picrate and 1D structure. The complex was explored for degradation of methylene blue (MB) and methyl orange (MO) dyes and the degradation values were 80.9 % and 83.7 % for MB and MO respectively. The effects of catalyst dosage, dyes concentration and pH on photocatalytic activity were also investigated systematically. The photocatalytic degradation mechanism elaborated pseudo-second-order kinetics with a rate constant of 0.0106 min−1. Additionally, the recyclability test revealed that the complex has photocatalytic effectiveness even after being used five times in succession. Studies on scavenging showed that ‧OH radicals and H+ are the main reactive species that break down substances. The results showed that compound 1 is a proficient and cost-effective catalyst for the degradation of MB and MO dyes. We performed a Hirshfeld surface analysis to understand the intermolecular interactions and packing within the crystal structure. The most prominent intermolecular interactions were H‧‧‧O/O‧‧‧H contacts, which accounted for 49.1 % of the Hirshfeld surface. This indicates a significant role of hydrogen bonding in stabilizing the crystal structure.