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 μM for DMAET and DEAET were obtained with sensitivities of 5.0 and 6.0 × 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.