Abstract
Donor and acceptor phthalocyanine molecules were copolymerized and linked to graphene oxide nanosheets through amidation to yield electrocatalytic platforms on glassy carbon electrodes. The platforms were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, UV/Vis spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The fabricated electrochemical catalytic surfaces were then evaluated toward electrocatalytic detection of ascorbic acid and tryptophan. These were characterized by a wide linear dynamic range and low limits of detection and quantification of 2.13 and 7.12 µM for ascorbic acid and 1.65 and 5.5 µM for tryptophan, respectively. The catalytic rate constant was 1.86 × 104 and 1.51 × 104 M−1s−1 for ascorbic acid and tryptophan, respectively. The Gibbs energy for catalytic reactions was −17.45 and −14.83 kJ mol−1 depicting a spontaneous reaction on the electrode surface. The sensor platform showed an impressive recovery when applied in real samples such as fresh cow milk, in the range 91.71–106.73% for both samples. The developed sensor therefore shows high potential for applicability for minute quantities of the analytes in real biological samples.
Highlights
The electrocatalytic behavior of non-precious metals is enhanced when incorporated in macrocyclic ensembles such as phthalocyanines and porphyrins (Nyokong and Khene, 2016)
We have reported the use of polymer-appended phthalocyanines (Mafuwe et al, 2018) and carbon nanotube–appended phthalocyanines (Shumba and Nyokong, 2017) among other manipulations, and we have shown how these can be used as electrode modifier materials
We explore the effect of substituent groups on the electrocatalytic behavior of phthalocyanines
Summary
The electrocatalytic behavior of non-precious metals is enhanced when incorporated in macrocyclic ensembles such as phthalocyanines and porphyrins (Nyokong and Khene, 2016). We have recently shown that the inclusion of carbon-based nanomaterials has resulted in improved electron flow and enhanced redox capabilities of the metal center in the macrocyclic ensemble (Shumba and Nyokong, 2016a). The approaches such as nanosizing and polymerization alike discourage aggregation which is prominent in phthalocyanines. 2017), this work explores for the first time prepolymerization of differently substituted phthalocyanines This was achieved through amidation of carboxylate- and amine-terminated phthalocyanines as described before (Moyo et al, 2016; Shumba and Nyokong, 2017), Scheme 1A. Electrodes as described before, and the resultant electrodes were named GO/GCE, CoTAPc/GCE, CoTCPc/GCE, poly-CoTAPcCoTCPc-GCE, poly-CoTAPc-CoTCPc-GONS/GCE, and CoTAPc-GONS/GCE
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