Multi-wall carbon nanotubes (MWCNTs) and Nation composite film (MWCNTs/Nafion) were used for fabricating electrochemical sensors for the voltammetric detection of trace lead(Ⅱ) and cadmium(Ⅱ) in several water samples. The morphology and structure of MWCNTsfNafion film were characterized by scanning electron microscopy (SEM) and infrared spectrum (IR). The electron transfer of MWCNTs/Nafion composite film was examined by cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS). Various experimental parameters, which influenced the response of MWCNTs/Nation/GC to target metals, were optimized. The results showed that the synergistic effect was obtained on the MWCNTs/Nafion/GC whose sensitivity and stability were better than those of Nation-coated electrode (Nafion]GC) or CNTs/GC. Stability of the Pb(II) and Cd(Ⅱ) stripping signals was excellent with relative standard deviations (RSD) within 5% (n = 10) from one electrode preparation to another, and RSD of 30μg.L^1 Pb(Ⅱ) and Cd(Ⅱ) were 2.8% and 3.2% for 20 repeated analysis on one single CNTs/Nafion/GC. Over 50 runs, the stability of Pb and Cd detection at the MWCNTs/Nafion conposites electrode was still satisfactory with RSD lower than 6.0%. The determination limits (S/N=3) of the proposed method were determined to be 100 ng·L^-1 for Pb and 150 ng.L^-1 for Cd. Finally, the MWCNTs/Nafion/GC was successfully applied to determine Pb(Ⅱ) and Cd(Ⅱ) in different water samples with recoveries of 97%-103% for Pb and 96%-104% for Cd.
A simple and sensitive electroanalytical method was presented for the determination of 4-n-octylphenol (OP) based on multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE). OP was directly oxidized on the MWCNTs/GCE, and the electrochemical oxidation mechanism was demonstrated by a one-electron and one-proton process in the reaction. The oxidation peak current of OP was significantly enhanced by the use of MWCNTs/GCE compared with those of bare glassy carbon electrode, suggesting that the modified electrode can remarkably improve the performance for OP determination. Factors influencing the detection processes were optimized. Under these optimal conditions, a linear relationship between concentration of OP and current response was obtained in the range of 5 × 10-8 to 1× 10-5 mol/L with a detection limit of 1.5 × 10-8 mol/L and correlation coefficient 0.9986. The modified electrode showed good selectivity, sensitivity, reproducibility and high stability.
A simple and rapid approach for the electrochemical synthesis of Ag nanoparticles-coated gold nanoporous film (AgGNF) on a gold substrate was reported. The solid gold electrode (SGE) was directly anodized under a high potential of 5 V, and then reduced to obtain gold nanoporous film (AuNF) by freshly prepared ascorbic acid. The Ag nanoparticles (AgNPs) were grown on the AuNF electrode by potential-step electrodeposition. The resulting AgGNF composites electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and cyclic voltammetry (CV). As-prepared AgGNF electrode was used as a kind of superior sensor for Cr(VI) detection, which exhibited better electrocatalytic behavior than those of AuNF and SGE under identical conditions. Such a designed AgGNF nanocomposites electrode showed outstanding sensitivity (about 0.15 nA/ppb) and favorable reproducibility for Cr(VI) detection. The dependence of reduction current on Cr(VI) concentration is linear from 2 to 370 ppb with a low detection limit of 0.65 ppb. Interferences from other heavy metals ions (Cr3+, Cu2+, Pb2+, As3+ and Hg2+) associated with Cr(VI) analysis could be effectively diminished. The present method proves to be rapid, reliable, sensitive and low-cost.