Sensitive Electrocatalytic Assay of Cyclotetramethylene Tetranitramine (HMX) Explosive on Carbon Nanotube/Ag Nanocomposite Electrode

An efficient electrocatalyst was developed based on silver nanoparticles/multi walled carbon nanotubes nanocomposite modified glassy carbon electrode (AgNPs/MWCNTs/GCE) by controlled electrodeposition and continuous double-potential pulses to test the high explosive cyclotetramethylene-tetranitramine (HMX) using cyclic voltammetry method. The electrochemical behavior of the system in various pHs was studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), chronoamperometry and chronocoulometry; and some reduction parameters, including the transfer coefficient (α), electron transfer number, apparent electron transfer rate, and diffusion coefficient constants of HMX were estimated. The results demonstrated that reduction of HMX by adsorptive stripping voltammetry on AgNPs/MWCNTs film could remarkably be enhanced and catalyzed compared to bare carbon nanotubes electrode, and the reduction potential could be facilitated from -0.7 V (vs. SCE) to -0.3 V, with electron exchange rate constant of 1.12±0.1 s-1 and 0.17 ±0.1 s-1 for AgNPs/MWCNTs and bare MWCNTs electrodes. Chronoamperometry studies showed a diffusion-controlled process with an apparent diffusion coefficient of 2.01×10−4 cm2 s−1 and a catalytic rate constant of 7.48 times higher than that of bare MWCNTs electrode. Also, chronocoulometric studies showed that the number of electrons transferred for electrochemical reduction of HMX was near 1.98. Under optimized conditions, the reduction peak had two linear dynamic ranges of 2.0-30.0 and 30.0-120.0 mM with the experimental detection limit of 0.2 mM and precision of <2.5% (RSD for five analyses). This modified electrode can be properly used to determine HMX in soil and groundwater samples with satisfactory results.