Modified carbon nanoparticle-chitosan film electrodes:: Physisorption versus chemisorption

Surface functionalised carbon nanoparticles of ca. 8 nm diameter co-assemble with chitosan into stable thin film electrodes at glassy carbon surfaces. Robust electrodes for application in sensing or electrocatalysis are obtained in a simple solvent evaporation process. The ratio of chitosan binder backbone to carbon nanoparticle conductor determines the properties of the resulting films. Chitosan (a poly-D-glucosamine) has a dual effect (i) as the binder for the mesoporous carbon composite structure and (ii) as binding site for redox active probes. Physisorption due to the positively charged ammonium group (pK(A) approximate to P 6.5) occurs, for example, with anionic indigo carmine (a reversible 2e(-)-2H(+) reduction system in aqueous media). Chemisorption at the amine functionalities is demonstrated with 2-bromo-methyl-anthraquinone in acetonitrile (resulting in a reversible 2e(-)-2H(+) anthraquinone reduction system in aqueous media). Redox processes within the carbon nanoparticle-chitosan films are studied and at sufficiently high scan rates diffusion of protons (buffer concentration depended) is shown to be rate limiting. The chemisorption process provides a much more stable interfacial redox system with a characteristic and stable pH response over a pH 2-12 range. Chemisorption and physisorption can be employed simultaneously in a complementary binding process. (C) 2008 Elsevier Ltd. All rights reserved.