Electrochemical properties of surface-confined films of single-walled carbon nanotubes functionalised with cobalt(II)tetra-aminophthalocyanine: Electrocatalysis of sulfhydryl degradation products of V-type nerve agents

This paper describes detailed comparative electrochemical and electrocatalytic behaviours of basal plane pyrolytic graphite electrodes (BPPGEs) modified with single-wall carbon nanotube (BPPGE-SWCNT) and SWCNTs functionalised with cobalt(II) tetra-aminophthalocyanine by physical (BPPGE-SWCNT-CoTAPc((mix))), chemical (BPPGE-SWCNT-CoTAPc((cov))) and electrochemical adsorption (BPPGE-SWCNT-CoTAPc((ads))) processes. SWCNT improves both solution and surface electrochemistry of CoTAPc. Electrochemical kinetics of the SWCNT-CoTAPc modified BPPGE yielded different k(s) values, indicative of different rate-determining steps for the cathodic and anodic reactions. Electrochemical impedance spectroscopy (EIS) analyses in the presence of [Fe(CN)(6)](3-/4-) as a redox probe revealed that the SWCNT and SWCNT-CoTAPc((mix)) films have comparable data in terms of solution resistance (R-s), electron transfer resistance (R-et), Warburg impedance (Z(w)) and electron-transfer rate constant (k(app)). Also, these surface-confined films showed comparable electrocatalytic responses towards the detection of V-type nerve agent sulfhydryl hydrolysis products, dimethylaminoethanethiol (DMAET) and diethylaminoethanethiol (DEAET). Using the BPPGE-SWCNT-CoTAPc((mix)), the estimated catalytic rate constants and diffusion coefficients were higher for DEAET than for the DMAET. Also, the detection limits of approximately 8.0 and 3.0 mu M for DMAET and DEAET were obtained with sensitivities of 5.0 and 6.0 x 10(-2) A M-1 for DMAET and DEAET, respectively. BPPGE-SWCNT-CoTAPc showed better potential discrimination for detection of these sulfhydryl analytes than the BPPGE-SWCNT, the latter exhibited enhanced catalytic response for the sulfhydryls than the former. (c) 2006 Elsevier Ltd. All rights reserved.