Nano-Asterisks of Vanadium Dioxide As Electrodes for TNT Detection

Tuesday, 26 May 2015: 15:40
PDR 6 (Hilton Chicago)
D. Cliffel, M. Casey, and A. Daniel (Vanderbilt University)
Vanadium dioxide (VO2) is a unique transition metal oxide that undergoes a first-order phase transition at approximately 340K from the insulating monoclinic phase (M) to the conducting rutile phase (R). This metal-to-insulator transition (MIT) results in a change in the resistivity and optical absorption of the material, which has made it useful in several electronic and electro-optic applications. Common synthetic techniques such as pulsed laser deposition (PLD), chemical vapor deposition (CVD), and magnetron sputtering allow for the synthesis of high quality films of VO2 for these applications. Recently, however, hydrothermal methods have been used for the synthesis of relatively large quantities of VO2(M) from inexpensive starting materials without the need for expensive instrumentation. While these hydrothermally synthesized VO2(M) particles are being developed for electronic and electro-optic applications, their applicability in other areas, such as catalysis and sensing, is the focus of research in our group. 

To make nano-asterisks of VO2, the amount of vanadium precursor present during a hydrothermal treatment was varied to produce several different morphologies of VO2(M) including plates, snowflake asterisks, and truncated asterisks.  Films of the particles were drop cast onto glass slides and four-point Van der Pauw resistivity measurements were used to determine the phase transition behavior of the particle films.  We observe resistivity changes of more than 2 orders of magnitude for drop cast films of VO2(M) nano-asterisks.  Additionally, BET gas adsorption theory was used to determine the surface area of the particles in order to evaluate their potential as electrocatalytic materials. 

The electrochemical reduction of 2, 4, 6-Trinitrotoluene (TNT) was investigated using films of vanadium dioxide, from both thin layer films formed by PLD and films composed of nano-asterisks particles. Three distinct reduction peaks were observed in the potential range -0.50 V to -0.90 V (vs. an Ag/AgCl reference electrode), corresponding to the electrochemical reduction of the three nitro-groups on the TNT molecule. Adsorptive stripping voltammetry was performed to achieve detection down to 1 µg/L (4.4 nM), revealing a linear response to TNT concentration. These results are the first describing the use of VO2 films as an electrochemical sensor for TNT, and open new avenues for further electrochemical research using this unique material.