Electrochemistry of Carbon Nanotube Composite Electrodes

Carbon nanotubes can be considered as molecular-scale wires with high mechanical strength and different electronic properties (metallic, semiconducting or semimetallic) depending mainly on the tube symmetry [14]. These properties have been utilized for the development of various electrochemical sensors for monitoring gases as NO2 or NH3 [5], the oxidation of biomolecules (dopamine, ascorbic acid, etc.) [6,7], the investigation of protein electrochemistry [8] and the electrocatalytic reduction of oxygen [9]. Most of the above sensors are mixtures of the nanotubes with inert organic binders (bromoform, Nujol or liquid paraffin) [79]. Other sensors schemes include the construction of electrodes based on single nanotubes attached to a Pt tip [10] or the use of whiskers of loosely packed multi-wall carbon nanotubes (MWNT) [11,12]. The sol-gel chemistry involves the fabrication of ceramic materials via the hydrolysis and condensation of suitable alkoxysilane precursors [13]. Sol-gel technology has been widely used for the development of chemical sensors and biosensors since it provides a relatively simple way to incorporate recognition species in a stable host environment [14,15]. Several sol-gels have been used in conjunction with carbon powder [16-18] or gold particles [19,20] for the construction of composite electrodes. The applications of those electrodes include biosensing [1820], chromatographic detection [21-23] and electrocatalysis [16,24]. In the present work new composite electrode materials were designed and characterized by combining carbon nanotubes and sol-gel technology. The multi-wall carbon nanotubes were dispersed into different types of sol-gel matrix for the construction of the electrode. The effect of the sol nature and the amount of the carbon nanotube on the electrochemical behavior of the composites electrodes is investigated.