Preparation and characterization of thin films of amine functionalised mesoporous silica having cubic pore structures and their use for electrode surface modifications

Thin films of amine functionalised mesoporous silica were deposited on tin-doped indium oxide (ITO) slides by dip-coating mixtures of TEOS (tetraethyl orthosilicate), APTES((3-aminopropyl)triethoxysilane), and the non-ionic surfactant Brij56. The pore structure of the films was found to depend on the temperature use during calcination to remove the templates. Films calcined at 350 degrees C had highly ordered mesostructures with face-centred cubic pore arrangements, while films calcined at 275 degrees C had primitive Cubic pore structures. The as-prepared films, or films extracted with acidic ethanol solutions had very poorly ordered mesopores. Calcination at 275 degrees C was sufficient to remove the Brij56 templates, without damaging the organic amine chains. Calcination at 350 degrees C however, also resulted in the lost of the organic groups. The use of ITO substrates allowed the dip-coated films to be used directly as working electrodes. At pH 4.7, the voltammetric response of [Ru(bpy)(3)](2+) was completely suppressed by the amine functionalised films. This was attributed to protonation of the amine groups that gave the films positive charges. At higher pH, the amine groups were no longer protonated and the voltammetric response of [Ru(bpy)(3)](2+) was restored. Conversely, [Ru(bpy)(3)](2+) Was adsorbed by the unmodified films that carried negative charges at pH 4.7, resulting in a 4-fold increase in the peak currents compared to uncoated ITO. For [Fe(CN)(6)](3-) at low pH the unmodified films blocked the response of the ions, while the functionalised films gave small but distinct voltammetric peaks. (C) 2008 Elsevier Inc. All rights reserved.