Electrochimica Acta 112 (2013) 333–341 Contents lists available at ScienceDirect Electrochimica Acta jo u r n al hom ep age: www.elsevier.com/locate/electacta Clay-mesoporous silica composite films generated by electro-assisted self-assembly Adela Maghear a,b , Mathieu Etienne a , Mihaela Tertis ¸ b , Robert S˘ andulescu b , Alain Walcarius a,∗ a Laboratoire de Chimie Physique et Microbiologie pour l’Environnement, UMR 7564, CNRS – Université de Lorraine, 405 rue de Vandoeuvre, F-54600 Villers-lès-Nancy, France b Analytical Chemistry Department, Faculty of Pharmacy, “Iuliu Hat ¸ ieganu” University of Medicine and Pharmacy, 4 Louis Pasteur St., 400349 Cluj-Napoca, Romania a r t i c l e i n f o Article history: Received 18 July 2013 Received in revised form 23 August 2013 Accepted 26 August 2013 Available online xxx Keywords: Clay Sol–gel silica Composite thin films Electrochemically-assisted deposition Modified electrode Permeability a b s t r a c t This work describes the electro-assisted generation of clay-mesoporous silica composite films onto glassy carbon electrodes (GCEs). The method involved the deposition of clay particles by spin-coating on GCE and the subsequent growing of a surfactant-templated silica matrix around these particles by electro-assisted self-assembly (EASA). EASA typically consisted in applying a cathodic potential to the electrode immersed into a hydrolyzed sol (containing tetraethoxysilane, TEOS, as the silica source, and cetyltrimethylammo- nium bromide, CTAB, as surfactant) in order to generate the necessary hydroxyl catalysts inducing the formation of the mesoporous silica. In such conditions, alongside the silica deposition process, the inter- layer distance between the clay sheets was found to increase as a result of CTAB ion exchange. After removal of the surfactant template, the composite film became highly porous (i.e., to redox probes) and the clay recovered its pristine interlayer distance and cation exchange properties. This made it promis- ing for application in preconcentration electroanalysis, as pointed out here using copper(II) as a model analyte, especially because it offered much better long-term operational stability than the conventional (i.e., without silica binder) clay film electrode. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Structuration of electrode surfaces with inorganic thin films has become a well-established field of interest, notably for applica- tions in electroanalysis [1–21]. Various materials have been used for that purpose, including zeolites [2–5], clays [6–9] and lay- ered double hydroxides [10,11], silica [3,12,13] and silica-based organic–inorganic hybrids [13,14], sol–gel materials [14–17] and, more recently, ordered mesoporous materials [3,18–21]. The driv- ing force to select one or another of these electrode modifiers often relies on the particular properties (ion exchange, selec- tive recognition, hosting capacity, size selectivity, redox activity, permselectivity, etc.) which can be useful to the final application (preconcentration electroanalysis, electrocatalysis, permselective coatings, biosensors, . . .). As most of these materials are electronic insulators, their use in connection to electrochemistry requires a close contact to an electrode surface, which can be basically achieved via dispersion of as-synthesized powdered materials in a conductive composite ∗ Corresponding author. Tel.: +33 3 83 68 52 43, fax: +33 3 83 27 54 44. E-mail address: alain.walcarius@univ-lorraine.fr (A. Walcarius). matrix (e.g., carbon paste electrodes [22]) or deposited as thin films on solid electrode surfaces. In the latter case, a critical point is the uniformity and long-term mechanical stability of the thin coatings, which might be challenging when attempting to deposit particulate materials onto electrodes, requiring often the use of an additional polymeric binder [23]. This is especially the case of zeolite film modified electrodes, the situation being somewhat less problem- atic for clay film modified electrodes because of the particular platelet morphology of clay particles and their self-adhesive prop- erties toward polar surfaces [24] ensuring better interaction with most electrode materials and consequently more durable immobi- lization. Nevertheless, besides the classical physical attachment of a clay film to a solid electrode surface (through solvent casting, spin- coating or layer-by-layer assembly as the mainstream techniques [6,24,25], or electrophoretic deposition [26]), other strategies based on covalent bonding (via silane or alkoxysilane coupling agents) have been also developed [27,28]. On the other hand, the versatility of the sol–gel process makes it especially suitable to coat electrode surfaces with uniform deposits of metal or semimetal oxides (mainly silica) and organic–inorganic hybrid thin films of controlled thickness, composition and porosity. The method is intrinsically simple and exploits the fluidic character of a sol (typically made of alkoxysilane precursors for silica-based 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.08.119