Mesoporous silica films for sensing volatile organic compounds using attenuated total reflection spectroscopy

Sensitivity of evanescent wave sensing of gaseous species can be vastly increased by enrichment materials that locally concentrate the analyte on the sensor. Here, we investigate functionalized mesoporous silica films as versatile enrichment layer for sensing volatile organic compounds (VOCs) from gas-phase. Attenuated total reflection (ATR) crystals were coated with silica films of different pore sizes and their capability to enrich three different aromatic hydrocarbons from a vapor stream was studied by means of Fourier Transform infrared (FTIR) spectroscopy. Thereby, single-digit ppmv limits of detection (LOD) were achieved with an effective path length of only 6.3 μm. The selectivity introduced by the functionalization of the silica films effectively minimized interferences of water vapor, which gave access to the spectral fingerprint region between 1550 and 1450 cm-1. This allowed to discriminate and quantify toluene, p-xylene and 1,2,4-trimethylbenzene in multicomponent mixtures at high humidity. Fast response and regeneration times and enrichment factors up to 32 000 showcase the high potential of this material for evanescent wave sensing.