Sensitive Detection of Dichlorvos Pesticide in Aqueous Phase using a Cobalt (II) Coordination Polymer based on Biphenyl-4-carboxylic acid

Abstract

ABSTRACTA cobalt-based coordination polymer (CP), [Co(Biphen)2(Tmp)2] n.(H2O), was successfully synthesised andcharacterised using Fourier-Transform Infrared Spectroscopy (FTIR), ultraviolet visible spectroscopy (UV-Vis),Thermogravimetric analysis (TGA), and Scanning Electron Microscopy (SEM). The MOF appeared as a bluecrystalline solid with a melting point of 257 °C and a molecular weight of 889.92 g/mol. It was slightly soluble inDimethy sulphoxide (DMSO) but insoluble in ethanol, methanol, n-hexane, Dimethylformamide (DMF), and water.FTIR analysis revealed shifts in the C=O band from 1684 cm-1 in the free Biphen ligand to 1681 cm⁻1 in the complex,as well as the appearance of carboxylate (COO-) symmetric and asymmetric stretching bands at 1608 cm-1 and 1535cm-1, respectively, with a Δν value of 73 cm-1, confirming a chelating bidentate coordination mode. Additional Co-Oand Co-N stretching bands appeared at 516 and 621 cm-1, respectively. UV-Vis spectra exhibited ligand-based π→π*/n→π* transitions and d-d transitions characteristic of octahedral Co(II) centers. TGA revealed three decompositionstages with high thermal stability. SEM analysis revealed aggregated, porous micro- to nanosized particles with acauliflower-like morphology. The compound showed a distinct emission band at 630 nm upon excitation at 318 nm.This was attributed to ligand to metal charge transfer (LMCT) because of cheating the metal to the ligand. Thecompound also showed high selectivity towards dichlorvos pesticide among other organic compounds tested vialuminescence sensing. Keywords: Coordination polymers, Detection, Fluorescence, Pesticide, Quenching