One-pot solvothermal synthesis of octahedral 3D copper (II) MOF and its performance evaluation towards electrochemical sensing of Malathion pesticide and adsorption of Congo red dye

Pesticide and dye residues in water bodies have become a global problem, as they bio-accumulate in organisms and adversely disturb the balance of ecosystem. A 3D truncated octahedral Cu MOF was synthesised by the Solvothermal approach and evaluated for the adsorption of Congo red dye (CRD) and the electrochemical detection of Malathion pesticide in water. Various characterisation techniques have been employed to assess the surface morphology, crystalline behaviour, availability of functional groups, porosity, and the chemical state of the as-synthesised Cu MOF. Differential pulse voltammetry (DPV) was used to quantify Malathion in a 0.1 M PBS (pH 7) electrolyte solution. The Cu MOF-modified glassy carbon electrode (GCE) exploits the strong interaction between copper centres and the sulphur groups in Malathion, allowing effective binding and signal transduction. The sensor exhibits higher electron-transfer rate and selectivity, with a linear range of 0.2–25 µM and a detection limit of 120 nM. The practical applicability of sensor was verified by spiking Malathion pesticides in tap water and garden soil, with recovery rates ranging from 96% to 104%. Additionally, batch experimental studies conducted under optimised conditions, using 10 mg/L of CRD and 6 mg of Cu MOF as the adsorbent, yielded a removal efficiency of 99.3% at neutral pH and ambient temperature along with the adsorption capacity of 96 mg/g. This 3D Cu MOF can be recycled for five adsorption-desorption cycles. The thermodynamic study reveals that adsorption isotherm fits well with Langmuir model, and reaction kinetics follow pseudo-second order kinetics.