2.4. Fabrication of Cu/Ce-MOF/NZP/CPE

The carbon paste electrodes were prepared using graphite powder and paraffin oil (2 drops) as binder. The components of 0.15 g in total weight in the absence and presence of modifiers (1.3% NZP, and 2.7% Cu/Ce-MOF) were mixed thoroughly in a mortar for at least 25 min to obtain homogeneous paste. Then, the paste was packed into one end of a polyethylene insulin syringe in 0.4 cm deep, and a copper wire passing through the center of the electrode body for electrical contact. The surface of each electrode was polished using a suitable paper to produce a smooth, shiny and reproducible working surface. Then, the prepared electrode was washed with deionized water to remove impurities. The Cu/Ce-MOF/NZP/CPE electrodes were fabricated by employing different amounts of Cu/Ce-MOF and NZP modifiers in paste composition.