chapter  4
5 Pages

IMIDAZOLIUM-BASED IONIC LIQUID FUNCTIONAL MATERIALS AND THEIR APPLICATION TO ELECTROANALYTICAL CHEMISTRY

ILs of interesting properties. For the overall environmental impact and economics, they were employed as solvents for electrochemistry [2-8], analytical chemistry [9], chemical synthesis [10-14], liquid/liquid separations and extractions [15-17], dissolution [18-20], catalysis [21-25], and polymerization [26]. In electrochemistry, they show relatively wide potential window and high conductivity and allow studies to be undertaken without additional supporting electrolyte [27]. Thus various applications including in electrodeposition, electropolymerization, capacitors, Li-ion batteries, and solar cell have been intensive investigated [28]. ILs have also offered many opportunities in electroanalytical chemistry [29]. Particularly, some task-specific ILs have also been designed because the structures and properties of ILs can be easily tuned by selecting proper combination of organic cations and anions. Equally importantly, these unique properties of ILs could be extended to the concept of task-specific IL-materials. No longer as simple green solvents, it would greatly expand the potential application of ILs. As excellent reviews exist describing ILs for analytical chemistry, electroanalytical chemistry or electrochemistry [9, 28-31], here we will focus on the imidazolium-based IL-materials and their applications in electroanalytical chemistry from our laboratory as well as other groups. 4.2 ELECTROSYNTHESISILs show a relatively wide potential window and high conductivity and allow studies to be undertaken without additional supporting electrolyte. Recently, Aida et al. have reported sing-walled carbon nanotubes (SWNTs) could be considerably untangled into much finer bundles that are physically cross-linked in ILs [32]. Thus, we were motivated to design a kind of RTIL-supported three-dimensional network SWNT electrode (as shown in Fig. 4.1a) [33]. The advantage of bucky gels of ionic

liquids and SWNTs for the electrochemical functionalization of SWNTs is that the ionic liquid acts as both a dispersant of SWNTs and a supporting electrolyte. More important, it would greatly increase the effective surface area of the SWNT electrode, and the homogeneous electrochemical functionalization of the SWNTs performed well even in large quantities. This is rare for conventional electrochemical functionalization of SWNTs because the reaction occurs locally on a limited surface of bundled SWNTs deposited on metal electrodes. N-succinimidyl acrylate (NSA), as a model monomer, which bears an active ester group, was ground into a gel of ILs and SWNTs, and the mixture was placed onto gold electrode. NSA was electrografted and polymerized onto SWNTs (SWNTs-poly-NSA) by applying a reduction potential to the electrode (Fig. 4.1b). The active ester groups in the grafted poly-NSA can be utilized for further functionalization. For example, by the reaction with glucose oxidase (GOD), the modified SWNTs with an electrocatalytic activity toward glucose can be fabricated, which could be utilized as biosensor toward glucose (Fig. 4.1c). Similarly, Wei et al. have utilized the same method to functionalize SWNTs with polyaniline [34].In addition, ILs could also be used as both solvent and electrolyte for the electrodeposition of copper [35, 36], aluminum [37, 38], tantalum [4], platinum [39], silver [40, 41], gold [40-42], and silicon [43]. For example, Endres et al. have reported the electrodeposition of nanocrystalline metals and alloys, such as aluminum from ILs, which previously could not be electrodeposited from aqueous or organic solutions. This method enabled the synthesis of aluminum nanocrystals with average grain sizes of about 10 nm, Al-Mn alloys, as well as Fe and Pd nanocrystals [4] (as shown in Fig. 4.2).