Abstract
This paper describes the electrocatalytic behaviour of a glassy carbon electrode (GCE)modified with cobalt(II)phthalocyanine (CoPc) complex peripherally tetrasubstituted withcobalt(II)tetraphenylporphyrin (CoTPP) complexes via ether linkages (i.e., CoPc-(CoTPP)4). Thefeatures of the immobilised pentamer were interrogated with cyclic voltammetry andelectrochemical impedance spectroscopy (EIS) using [Fe(CN)6]3-/4- as redox probe revealedenhanced electron transfer properties with kapp ≈ 18 x 10-6 cms-1 compared to that of the bareGCE (4.7 x 10-6 cms-1). The viability of this supramolecular complex as a redox mediator for theanodic oxidation and sensitive amperometric determination of hydrazine in alkaline conditions isdescribed. The electrocatalytic oxidation of hydrazine by GCE-CoPc-(CoTPP)4 was characterisedwith satisfactory catalytic current response with low non-Faradaic current (ca. 30 times lowerthan the bare GCE) and at much lower oxidation potential (ca. 300 mV lower than the bareGCE). A mechanism for the studied electrocatalytic reaction was proposed based on thespectrophotometric evidence that revealed the major involvement of the Co(III)/Co(II) redox coupleof the central CoPc species rather than the CoTPP component of the pentamer. Rate constant forthe anodic oxidation of hydrazine was estimated from chronoamperometry as ~ 3x103 M-1s-1. Theproposed amperometric sensor displayed excellent charateristics towards the determination ofhydrazine in 0.2 M NaOH ; such as low overpotentials ( 100 mV vs Ag|AgCl), very fastamperometric response time (1 s), linear concentration range of up to 230 μM, with micromolardetection limit, high sensitivity and stability.
Highlights
Hydrazine (N2H4) is a powerful reducing agent, useful as a fuel in fuel cells [1]
These results clearly showed that the pentamer acts as a redox mediator by enhancing the electronic communication between the glassy carbon electrode (GCE) and the [Fe(CN)6]4/[Fe(CN)6]3- species, possibly by electrostatic attraction of the negatively charged probe and the positively charged cobalt centers of the pentamer
These results confirm that the immobilized CoPc-(CoTPP)4 solid thin film serves as an efficient electron transfer mediator between hydrazine and the GCE and the pentamer electrode can be successfully employed for the analysis of this important analyte
Summary
Hydrazine (N2H4) is a powerful reducing agent, useful as a fuel in fuel cells [1]. Hydrazine and its derivatives are frequently found in our environment, and are used as essential raw materials and intermediates in some industrial preparations such as pesticides, and suspected to be carcinogenic and mutagenic [2]. Electrodes modified with macrocyclic transition metal complexes such as the metallophthalocyanines (MPcs) have been reported to be efficient catalysts for the oxidation of hydrazine. The application of the immobilised pentamer film as a viable potential electroctalyst for both the anodic oxidation and amperometric determination of hydrazine in alkaline pH conditions were studied. The mechanism of the electrocatalytic processes of hydrazine with the immobilised pentamer film was proposed based on the electrochemistry data and supported by solid UV-visible spectrophotometric investigations. This represents the first report on the use of a metallophthalocyanine-metalloporphyrin conjugate for the study of the electrocatalytic oxidation and detection of hydrazine
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