Controlled Mesostructures of Solid-Templated Silica: Preparation and Electrochemical Characterization

In the past decades, mesoporous silica materials characterized by well-ordered microstructure and size- and shape-controlled pores have attracted much attention for the development of functional thin films for advanced applications in catalysis and electrocatalysis, sensors and actuators, separation technologies, micro- and nano-electronic engineering and science [1-3]. In this work, a silica sol in mixture with a polystyrene latex suspension was deposited on ITO conductive glass supports modifying the dimension of the template (30, 60, 100 nm) and the number of successive multi-layered depositions. After the template removal, stable, homogeneous and reproducible transparent thin films were prepared, in which an interconnected porous structure was obtained. The morphological features and the physicochemical and optical properties of the films were studied by Dynamic Light Scattering (DLS), FE-SEM, AFM, UV-vis transmittance spectroscopy analyses. Moreover, a deep electrochemical characterization was also performed by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) measurements. In particular, the use of two redox mediator probes [(K4Fe(CN)6) and (Ru(NH3)6Cl3)], presenting opposite charge and different diffusional behaviour, allowed the comprehension of the mass and charge transfer phenomena in the silica negatively charged mesochannels (isoelectric point around 2-3), evidencing the effects of spatial confinement and charge selection properties (Figure 1). Figure 1. Cyclic voltammograms registered at electrodes modified with a single layer (a,b) or multilayers (c) of silica with different pore sizes (30, 60, 100 nm) in the presence of 3 mM (a) [Fe(CN)6]4-/[Fe(CN)6]3- and (b-c) [Ru(NH3)6]3+/[Ru(NH3)6]4+. Electrochemical results were also interpreted in the light of water contact angle measurements: samples surface wettability revealed to be a crucial parameter for the sensing properties of the films, in complete agreement with roughness data provided by AFM measurements, according to the Wenzel model. The easiness of preparation and the interesting properties of these devices pave the way towards their use in trace electroanalysis. References [1] M. Ogawa, Chem. Rec., (2017), 17, 217-232. [2] A. Walcarius, E. Sibottier, M. Etienne, J. Ghanbaja, Nature Mat., (2007), 6, 602-608. [3] F. Yan, X. Lin, B. Su, Analyst, (2016), 141, 3482-3495.