One-step co-intercalation of cetyltrimethylammonium and thiourea in smectite and application of the organoclay to the sensitive electrochemical detection of Pb(II)

Abstract

This work describes the preparation of organoclays by one-step co-intercalation of cetyltrimethylammonium ions (CTA+) and thiourea in various amounts within the interlayer region of smectite, and their use as electrode material for the detection of Pb(II). The physico-chemical properties of the intercalated clay mineral were first analyzed by XRD, N2 adsorption–desorption and FTIR. These techniques have demonstrated the successful intercalation of the modifiers in the interlayer region of the clay mineral, as evidenced by an extension of the d001 spacing, a decrease in porosity, and a change in FTIR patterns, all arising from the modification process. The electrochemical features and permeability properties of the organoclays, coated as thin films onto the surface of a glassy carbon electrode (GCE), were characterized through ion exchange multisweep cyclic voltammetry. Then, the organoclay film electrodes were exploited to build a sensitive and selective sensor for lead detection, thanks to the chelating ability of thiourea supported on the material. The optimal response was obtained for the functionalized clay mineral sample containing CTA+ ions at a concentration equivalent to 25% of the CEC and thiourea in excess of the CEC of the pristine clay mineral, showing a sensitivity higher by ca. one order of magnitude with respect to the unmodified electrode. The analytical performance of the developed method was evaluated and the experimental parameters governing the preconcentration electroanalysis of lead were optimized. A linear calibration curve for Pb(II) was obtained in the concentration range from 10−9 to 10−7M, with a detection limit of 2.9×10−11M (S/N=3), which is much lower than those usually reported in the literature. The interference effects of several cations on Pb(II) response were also evaluated, and the sensor was successfully applied to the detection of lead in tap water.