Tailoring Perfluorosulfonated Ionomer-Entrapped Sol−Gel-Derived Silica Nanocomposite for Spectroelectrochemical Sensing of Re(DMPE)3

The influence of the initial molar ratio of water relative to tetraethyl orthosilicate (TEOS) precursor and the content of Nafion ionomer in sol−gel-derived silica composites on the voltammetric response of electrodes modified with these composites for [ReI(DMPE)3]+ was investigated. The slow diffusion of [ReI(DMPE)3]+ in Nafion can be significantly improved by dispersing Nafion in sol−gel-derived silica, and the diffusion of [ReI(DMPE)3]+ in such a composite increases with the increase in water/TEOS molar ratio and the decrease in Nafion content. With the mass ratio of Nafion relative to sol−gel-derived silica being 40:100 and the initial molar ratio of water relative to TEOS being 20:1, the electrodes modified with the derived Nafion−silica nanocomposite exhibited an apparent peak current increase rate, during preconcentration of [ReI(DMPE)3]+, that was approximately three times faster than the corresponding Nafion-modified electrode. Compared with bare indium−tin oxide (ITO) glass, the composite-coated ITO glass showed a 25-fold enhancement in voltammetric response to [ReI(DMPE)3]+. The suitability of the developed optically transparent Nafion−silica composite for spectroelectrochemical sensing of [ReI(DMPE)3]+ was demonstrated. The [ReI(DMPE)3]+ extracted into the coating (∼0.4 μm in thickness) was electrolyzed to [ReII(DMPE)3]2+. Under attenuated total reflection mode, the in-situ electrogenerated chromophore [ReII(DMPE)3]2+ was monitored by probing its interaction with the evanescent field of light of a selected wavelength. Thus, the elements required for a spectroelectrochemical sensor with three modes of selectivity were demonstrated: partitioning into the film on an electrode surface and an electrochemically modulated optical signal.