Amino-grafting of montmorillonite improved by acid activation and application to the electroanalysis of catechol

Abstract

In this work, a natural sodium-montmorillonite clay mineral (Mt-Na) was functionalized with aminegroups, either by direct grafting (Mt-NH2) or via acid activation followed by grafting (MtH-NH2) of [3(2-aminoethyl)amino)]propyltrimethoxysilane (AEP-TMS). The morphology and structure of the resulting composite materials were characterizedby scanning electron microscopy, X-ray diffraction, N2 adsorption-desorption isotherms (BET method) infrared spectroscopy, CHN elemental analysis and thermogravimetric analyses (TGA). The obtained organoclays were then used to modify the surface ofa glassy carbon electrode (GCE), and the permselectivity and accumulation properties of the resulting films were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicated that MtH-NH2 modified GCE (GCE/MtH-NH2) exhibited some charge selectivity features and can be applied to the electrochemical oxidation of catechol (CT).By plotting the double logarithmic variation of anodic peak currents (Ipa) versus potential scan rate, the obtained slope valueof 0.49 revealed a diffusion-controlled electron-transfer mechanisms for the redox process. The electrochemical behavior of CT on the modified electrode was also studied using differential pulse voltammetry (DPV). The sensitivities of GCE/MtH-NH2 for CT were 1.71, 3.87 and 1.35-fold greater than signals obtained on the bare GCE, GCE/Mt-Na and GCE/Mt-NH2 respectively, due to the ability of the aminated materials to strongly accumulate CT. After optimization, GCE/MtH-NH2 was used for CT determination by differential pulse voltammetry that gave rise to a linear response in the concentration range from 5 μM to 80 μM (R2 = 0.999), and to a detection limit of 0.65 μM. The proposed method was applied to CT detection in water samples and in a tea sample.