Aerogel-platform optical sensors for oxygen gas

Abstract

We have developed aerogel-platform gas sensors that respond rapidly to changes in oxygen concentration. The aerogels are prepared via a novel one-step supercritical extraction technique, which employs a metal mold and a commercial hydraulic hot-press. The lack of a solvent extraction step facilitates the entrapment of probe species within the aerogel matrix. The three probes used, tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)32+], ruthenium(II)4,7-diphenyl-1,10-phenanthroline [Ru(dpp)32+], and platinum octaethylporphine [PtOEP], respond to variations in ambient oxygen concentrations through marked changes in their fluorescence intensity. The probe is added to a tetramethoxysilane (TMOS) precursor mixture before the mixture is poured into the mold; hence, the probe becomes physically entrapped within the aerogel matrix as it forms. We investigated the response of the probes to oxygen in xerogels and in aerogels. Both the aerogels and xerogels have high porosity, which allows for rapid diffusion of gases into these materials. The sensors respond rapidly and reversibly to changes in oxygen concentration. As oxygen concentration decreases, the Ru(dpp)32+ and PtOEP probe fluorescence intensities increase dramatically. The change in intensity of Ru(bpy)32+ is more modest. Ru(dpp)32+-doped aerogels and xerogels respond within 10s and 50s, respectively, whereas PtOEP-doped aerogels respond within 20s.