Synthesis, spectroscopic analysis and theoretical study of novel cobalt(II) complexes: Solar radiations-driven photocatalytic degradation of organic pollutants in wastewater

Abstract

The primary objective of this research is the synthesis of novel cobalt(II)-based mixed-ligand complexes, incorporating 2-hydroxyphenyl and a Schiff base ligand (L1) derived from cinnamaldehyde and mesalamine, designated as complexes 1 and 2. These complexes exhibit efficacy in detoxifying organic pollutants, specifically methylene blue (MB) and malachite green (MG), from wastewater. Spectral characterization of the ligand (L1) and the cobalt(II) complexes, 1 and 2, were performed using Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (¹H NMR) spectroscopy, cyclic voltammetry (CV), powder X-Ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), and ultraviolet–visible (UV–Vis.) spectroscopy. Additionally, molar conductance measurements, chloride estimation, and metal estimation were conducted and discussed. The molecular structures of L1, complex 1, and 2 were optimized by using Density Functional Theory (DFT) with B3LYP functional model and 6–311++G(d,p) basis set, and the corresponding parameters were thoroughly analyzed. Quantum chemical reactivity parameters for these synthesized complexes were predicted through charge distribution and molecular orbital analyses. Furthermore, the cobalt(II) complexes demonstrated effective photocatalytic degradation of MB and MG in aqueous solution, exhibiting high reusability. Complexes 1 and 2 showed exceptional selective photocatalytic efficiency towards the degradation of cationic dyes. Kinetic studies revealed that the degradation process adheres to the Langmuir-Hinshelwood kinetic model, achieving a maximum degradation efficiency of up to 96.5 % for the cationic dyes. Based on trapping experiments, a hypothetical mechanism for the observed photocatalytic performance was proposed.