AMPEROMETRIC SENSOR FOR HYDROGEN PEROXIDE BASED ON SOLID CARBON PASTE ELECTRODE MODIFIED WITH AN IRON-RICH NATURAL ZEOLITE

Zeolite modified carbon paste electrodes were widely used in electroanalytical applications [1-3]. Solid carbon pastes prepared using solid paraffin instead of mineral oil as the binder represent a new type of matrices, which have been used in zeolite modified carbon paste electrodes (ZMCPEs). These kinds of composite electrodes are more hydrophobic, preventing from impregnation by the electrolyte solution in the bulk electrode [1]. In this work we have prepared and characterized a new solid carbon paste electrode modified with an iron-based natural zeolitic volcanic tuff. The zeolitic volcanic tuff is cropped out from Paglisa (P) deposit (Cluj county, Romania). The sample was first used as an ionic exchanger in the process of iron and zinc removal from a wastewater resulted in the electrochemical plating process. Prior to this process zeolitic rock was brought to a granulation of 0.2-0.6 mm by grinding and size separation, then washed with distilled water and dried at 105°C. The exhausted ion exchanger was then dried, when P-Fe-Zn was obtained, and calcined at 400°C for 4 hours, when the P-Fe-Zn-c form was obtained. The zeolitic volcanic tuff, in unmodified (P) and modified (P-Fe-Zn, P-Fe-Zn-c) forms were characterized by means of chemical analysis, scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Fourier transformed infrared spectroscopy (FTIR), BET anaylsis and X-ray photoelectronic spectroscopy (XPS). Results of the analysis performed indicated that the samples are macroporous, specific surface areas was 15-20 m2/g, and that the main zeolite species identified is clinoptilolite (~70%). Also XPS analysis indicates that the iron content, as Fe(III), on the surface reached 2.07% in the modified samples. The electrochemical behaviour of solid ZMCPEs was investigated in buffered solutions at various pH values, using cyclic voltammetry. Then, their electrocatalytic properties for hydrogen peroxide reduction was investigated by amperometry under various experimental conditions (pH, applied potential). The analytical performance and response time of the obtained amperometric sensors were determined, optimized, and discussed with respect to the presence of iron centers in the materials.

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