Sensing layers for mass sensitive sensors prepared from tetraethoxysilane and organic modifiers for the detection of volatile organic compounds

Sol–gel derived materials (SGM) are widely used in analytical chemistry because of their easy preparation, chemical stability and the opportunity to vary the physical and chemical properties in a wide range by means of suitable modifiers. However, sol–gel derived materials are seldom employed as sensing layers of mass sensitive sensors. In the present paper, the suitability of organically modified silica layers as sensing material of mass sensitive sensors is studied, in particular for the detection of volatile organic compounds (VOCs). Sol–gel materials are prepared with tetraethoxysilane (TEOS) and organic modifiers (e.g., monoalkyl triethoxysilanes) as precursors. Model sensors are coated with sensing layers (thickness 10–100 μm) by an electrospray procedure. The coated model sensors are heat-treated at temperatures up to 600 °C using a thermogravimetric analyzer (TGA). Heat treatment causes the decrease of the mass of the sensing layer and the simultaneous increase of the sorption capacity and sorption rate for gaseous analytes. The sorption of VOCs is studied by direct measurement of the mass increase due to the sorption by the TGA. The sorption capacity depends mainly on the organic functionality of the modifier, the modifier concentration and the preceding heat treatment. A considerable increase of the sorption capacity is observed in particular after treatments at ≥400 °C. The influence of the preparation conditions, composition of the layer and heat treatment on the sensing properties is discussed.