Fabrication of Multi-Walled Carbon Nanotubes and Poly1,3,5-tri（2-thienyl）benzene Modified Glassy Carbon Electrode and Its Application in Determination of Trace Cu²⁺ in Environmental Water

In order to achieve simple, rapid, low-cost, and highly sensitive detection of trace Cu²⁺ in environmental water, the glassy carbon electrode modified with multi-walled carbon nanotubes （MWCNTs） and poly1,3,5-tri（2-thienyl）benzene （PTTB） （denoted as MWCNTs/PTTB/GC electrode） was prepared and applied to the detection of Cu²⁺ in lake water. The modified electrode was prepared by cyclic voltammetry （CV） for polymerization, and its morphology and composition were characterized by scanning electron microscopy （SEM） and attenuated total reflection infrared （ATR-IR） spectrometry, while its electrochemical behavior was characterized by CV, electrochemical impedance spectroscopy （EIS）, and Tafel curve. The lake water sample was passed through a 0.45 μm filter membrane, and an aliquot （5 mL） was taken. After mixing with 15 mL of acetic acid-sodium acetate buffer solution, the mixed solution was adjusted to pH 5 using acetic acid. Using the MWCNTs/PTTB/GC electrode as the working electrode, the platinum wire as the counter electrode, and the Ag/AgCl electrode as the reference electrode, Cu²⁺ was accumulated at constant potential of −0.8 V for 150 s using chronoamperometry, followed by a 20 s-rest period, and then detected by differential pulse voltammetry （DPV） in the range of −0.4−0.4 V. It was shown that the CV response, internal resistance, Tafel slope, and free corrosion potential of the MWCNTs/PTTB/GC electrode were significantly better than those of the GC electrode, indicating that the modification layer effectively enhanced the electron transfer efficiency and catalytic activity of the GC electrode, and the response of this modified electrode to Cu²⁺ was an adsorption-controlled irreversible process involving two-electron transfer. The mass concentration of Cu²⁺ showed a linear relationship with the DPV stripping peak current in the range of 0.5−200 mg·L⁻¹, with detection limit （3S/N） of 0.166 mg·L⁻¹. RSDs for repeatability （n=20） and reproducibility （n=5） tests were both less than 5.0%, and the stripping peak current of the modified electrode remained above 95% of its initial value after one week of storage. Common anions and cations, including K⁺, Ag⁺, Ca²⁺, Pb²⁺, Cd²⁺, Zn²⁺, SO₄²⁻, CO₃²⁻, Cl⁻, Mg²⁺, and Fe³⁺, did not interfere with the detection of Cu²⁺ （the absolute values of the relative difference in stripping peak current were less than 6.0%）. The method was applied to the analysis of lake water samples, and it was shown that the detected amount of Cu²⁺ was 19.15 mg·L⁻¹, and the recoveries at 4 spiked concentration levels ranged from 85.1% to 92.9%.