Simultaneous electrochemical detection of Cd2+ and Pb2+ using a green silver nanoparticles/polyaniline-modified carbon paste electrode

Abstract

In this study, a novel electrochemical sensor based on a carbon paste electrode (CPE) modified with polyaniline (PANI) and green-synthesized silver nanoparticles (AgNPs) was developed for the simultaneous detection of cadmium (Cd²⁺) and lead (Pb²⁺) ions in aqueous solutions. The AgNPs were synthesized using a green route employing plant extract as a reducing and capping agent, ensuring environmental sustainability. The modified electrode (AgNPs-PANI-CPE) was characterized by UV-Vis spectroscopy, field-emission gun scanning electron microscopy (FEG-SEM), and simultaneous thermal analysis (TGA/DSC). The electrochemical behavior of Cd²⁺ and Pb²⁺ was investigated using square wave voltammetry (SWV) and CV. The sensor exhibited distinct and well-separated anodic peaks for Cd²⁺ and Pb²⁺, with excellent sensitivity, wide linear response ranges, and low detection limits (0.09 and 0.05 μg L^-1, respectively). Interference studies demonstrated good selectivity towards the target ions, and successful application to real water samples confirmed its analytical performance. This work highlights the potential of eco-friendly nanocomposite-modified electrodes in environmental monitoring of toxic heavy metals.

Fig. 1. FEG-SEM images of: (A) polyaniline (PANI), (B) carbon paste electrode (CPE).

Fig. 2. The thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) data of polyaniline (PANI), with curve A (in blue) showing the TGA curve and curve B (in green) the DTG curve.

Fig. 3. (a) FT-IR spectra of olive leaves extract spectrum, (b) UV-Vis absorbance spectrum of green-synthesized AgNPs. (The curve shown is representative of three independent nanoparticle synthesis batches).

Fig. 4. Effect of (a) deposition potential, (b) deposition time on the anodic stripping peak current of Cd²⁺ and Pb²⁺ of 100.0 μg L⁻¹ to evaluate AgNPs-PANI-CPE sensor performance in 0.1 M acetate buffer (pH 4.5) and (c) anodic peak currents in acetate buffer as a function of pH (each point represents the mean ± standard deviation (SD) of three independent measurements).

Fig. 5. Cyclic voltammograms of AgNPs-PANI-CPE electrode at scan rates from 10 to 120 mV s⁻¹ in [Fe(CN)₆]^3−/4− solution. (Representative voltammograms from triplicate experiments).

Fig. 6. (A) Plot of anodic and cathodic peak currents vs. square root of scan rates; (B) peak currents vs. scan rates and (C) log of peak currents vs. logarithm of scan rates for AgNPs-PANI-CPE (all plots are based on average values from three independent measurements; error bars represent ± SD).

Fig. 7. (a) Nyquist diagram of CPE, PANI-CPE, and AgNPs-PANI-CPE [inset: the equivalent circuit], (b) CV curves of CPE, PANI-CPE, AgNPs-PANI-CPE in 5 mM [Fe(CN)₆]^3−/4− solution containing 0.1 M KCl at scan rate of 50 mV s^−1.

Fig. 8. Comparison of SWV on these three different electrodes for simultaneous detection of 4.8 μg L⁻¹ Cd²⁺ and Pb²⁺.

Fig. 9. A) Multi metal SWV of AgNPs-PANI-CPE in 0.1 M acetate buffer (pH 4.5) for the simultaneous detection of Cd²⁺ and Pb²⁺. (B) The corresponding the calibration curves.

Fig. 10. A) CV Curves for simultaneous analysis of AgNPs-PANI-CPE in 0.1 M acetate buffer (pH 4.5) containing [0.1–1] μg L⁻¹ of Cd²⁺ and Pb²⁺ at scan rate of 50 mV s⁻¹. (B) The corresponding: the calibration curve.

Fig. 11. Responses of AgNPs-PANI-CPE towards Cd²⁺ and Pb²⁺ in the presence of different interfering substances.

Fig. 12. SWV recorded in Cd²⁺ and Pb²⁺ in 0.1 M acetate buffer (pH 4.5) on AgNPs-PANI-CPE for (a) repeatability experiments and (b): sensor stability over a 14 days.