A QCM-based NO2 gas detector using morpholine-functional cross-linked copolymer coatings

Piezoelectric devices coated with cross-linked poly(styrene-co-chloromethyl styrene) reacted with morpholine were fabricated to develop a simple system that monitors NO2 gas in air. The introduction of NO2 gas irreversibly decreased the oscillation frequencies of all the devices tested, indicating that these devices can be used for one-shot detection of NO2 concentrations in air. The NO2 sensitivity was defined as hourly changes in frequency. The use of the cross-linked structure clearly increased sensitivity. The largest sensitivity obtained in this study was 1200 Hz/h for 50 ppm of NO2, which demonstrated a sub-ppm level of NO2 detection.