Stepwise improvement of (hetero-) polysiloxane sensing layers for CO2 detection operated at room temperature by modification of the polymeric network

Gas sensors based on the work function read out of (hetero-) polysiloxane sensing layers containing primary amino groups (–NH2) can be used for the detection of CO2. The sensing mechanism is assumed to be an acid/base reaction between primary amino groups and CO2. In literature, both a bicarbonate formation and a carbamate formation are discussed. To investigate the reaction with CO2, different polymers based on modified polysiloxanes are examined. It is shown that the CO2 response of work function type sensors can be systematically improved by modifying the polymeric network on the one hand (adjoining primary amino groups) and by increasing the hydrophobicity on the other hand. The findings summarized in this paper indicate the possibility for new ambient temperature CO2 sensors with short response (<1 min) and recovery times (<5 min), a high long-term stability (months to years) as well as a high SNR (signal noise ratio) of ca. 25 (exposure from 400 ppm up to 4000 ppm CO2). Furthermore, the fast establishment of the chemical equilibrium is remarkable when humidity is changed in atmosphere.