Determination of Trace Pb²⁺ and Cd²⁺ in Water by Electrochemical Method Based on Glassy Carbon Electrode Modified with COF@CNTs/Bi

A method for the determination of trace Pb²⁺ and Cd²⁺ in water by electrochemical method based on glassy carbon electrode modified with COF@CNTs/Bi was established. Single-wall carbon nanotubes of 0.1 g was taken, dimethyl sulfoxide of 25 mL was added, and the mixture was treated for 10 min with ultrasonic. Dialdehyde terephthalate of 0.02 g and 1,3,5-tri(4-aminophenyl) benzene of 0.035 g were added for ultrasonic treatment of 5 min. Then 12 mol·L^-1 acetic acid solution of 2 mL was added for ultrasonic treatment of 10 min. After washing 3 times repeatedly with N,N-dimethylformamide of 10 mL and anhydrous ethanol of 10 mL and drying, COF@CNTs was obtained. N,N-dimethylformamide of 5 mL was added to COF@CNTs of 1 mg for ultrasonic treatment of 5 min to get the suspension. The suspension of 5 μL was dropped onto the activated glassy carbon electrode surface to obtain COF@CNTs working electrode. Using COF@CNTs as the working electrode, Ag/AgCl as the reference electrode and platinum wire as the auxiliary electrode, the three-electrode system was placed in standard solution of Bi³⁺, Pb²⁺ and Cd²⁺. Bi³⁺, Pb²⁺ and Cd²⁺ were enriched for 360 s at -1.4 V to prepare COF@CNTs/Bi electrode. The stripping peak currents of Pb²⁺ and Cd²⁺ were recorded in the range of -1.4--0.2 V. As shown by the results, linear relationships between values of mass concentration of Pb²⁺ and Cd²⁺ and their stripping peak current were kept within 500 μg·L^-1, with detection limits (3S/N) of 0.33 μg·L^-1. Pb²⁺ and Cd²⁺ mixed standard solution of 100 μg·L^-1 was determined 5 times in parallel based on COF@CNTs/Bi electrode, and RSDs of the determined values was 3.9%. Recovery test was made on tap water and lake water, giving results in the range of 96.2%-108% and 95.3%-105%, respectively.