Due to health and pollution concerns of aquatic environments related to the presence of heavy metal toxic ions, the necessity of developing devices able to detect and to monitor such kinds of species has recently gained importance. Carbon paste electrodes (CPEs) a starting approach to obtain new ion-selective devices by supporting materials like bentonite and/or clay; which become sensitive to lead(II) when they are suitably modified by chemical treatments to obtain different hybrid materials. In this work, two natural clays and three different hybrid materials were produced and then were characterized by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy to assess their physico-chemical properties. After this stage, the electrochemical characterization of the modified CPEs using hybrid materials was performed by cyclic voltammetry, using the standard Fe(CN) 6 4− /Fe(CN) 6 3− redox couple. Subsequently, this study performed electrochemical experiments on lead(II) containing solutions, to test the ability of the examined CPEs to detect this toxic ion present in very low amounts. Lead(II) exhibited a reversible two electron oxidation/reduction behaviour in the cyclic voltammetry analyses and a reasonably good linear behaviour of the current associated with the oxidation peak as a function of its concentration (5.0-40.0 µg/L). The detection limit was found to vary in the range of 3-5 µg/L for the different modified CPEs. The presence of several co-existing ions showed that an interference variation had occurred. These results, therefore, show a restriction of the selectivity of the electrode up to a certain extent in the lead(II) detection. Finally, tap water with spiked lead(II) was analyzed to verify the suitability of the electrodes in the low level detection of lead(II) from real matrix samples.

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The carbon paste electrode (CPE) was modified with the pristine bentonite and hybrid material (HDTMA-modified bentonite). The modified-CPEs are then employed as working electrode in an electrochemical detection of As(V) from aqueous solutions using the cyclic voltammetric measurements. Cyclic voltammograms revealed that As(V) showed reversible behavior onto the working electrode. The hybrid material-modified carbon paste electrode showed significantly enhanced electrochemical signal which was then utilized in the low level detection of As(V). Moreover, the studies were conducted at neutral pH conditions. The electrochemical studies were conducted with scan rates (20 to 200 mV/s) to deduce the mechanism of redox processes involved at the electrode surface. The anodic current was linearly increased, increasing the concentration of As(V) from 5.0 to 35.0 μg/g using the hybrid material-modified electrode. This provided fairly a good calibration line for As(V) detection. The presence of varied concentrations of As(III) in the determination of total arsenic was studied. The influence of several cations and anions viz., Cu(II), Mn(II), Zn(II), Pb(II), Cd(II), Fe(III), Cl-, NO3-, PO4 3-, EDTA and glycine in the detection of As(V) from aqueous solution was also studied. Further, in an attempt to simulate the real matrix analysis, the tap water sample was spiked with As(V) and subjected for As(V) detection using the modified-CPE.

Novel silane grafted bentonite was obtained using the natural bentonite as precursor material. The material which is termed as nanocomposite was characterized by the Fourier Transform Infra-red (FT-IR) and X-ray diffraction (XRD) methods. The surface imaging and elemental mapping was performed using Scanning Electron Microscopic (SEM/EDX) technique. The electroanalytical studies were performed using the nanocomposite electrode. The electroactive surface area of nanocomposite electrode was significantly increased than the pristine bentonite or bare carbon paste based working electrode. The impedance spectroscopic studies were conducted to simulate the equivalent circuit and Nyquist plots were drawn for the carbon paste electrode and nanocomposite electrodes. A single step oxidation/reduction process occurred for As(III) having ΔE value 0.36 V at pH 2.0. The anodic stripping voltammetry was performed for concentration dependence studies of As(III) (0.5 to 20.0 μg/L) and reasonably a good linear relationship was obtained. The detection limit of the As(III) detection was calculated as 0.00360±0.00002 μg/L having with observed relative standard deviations (RSD) less than 4%. The presence of several cations and anions has not affected the detection of As(III) however, the presence of Cu(II) and Mn(II) affected the detection of As(III). The selectivity of As(III) was achieved using the Tlawng river water sample spiked with As(III).