Oxide nanoparticle arrays for sensors of CO and NO2 gases

Metal oxide sensors with active films from Fe2O3 and CoFe2O4 hexagonally assembled nanoparticle (NP) arrays were studied. NPs were synthesized by high-temperature solution phase reaction. Sensing NP layers were deposited by Langmuir–Blodgett (LB) technique. LB layers were characterized by XRD, SEM and magnetic measurements. NPs are monodomain and superparamagnetic at RT. Sensor active films are formed from 1 or 7 LB monolayers deposited on the alumina substrates equipped with heating meander and interdigitated contacts. LB layers were heat-treated or UV irradiated to remove the insulating surfactant. Sensing properties were studied in a test chamber containing reducing (CO) or oxidizing (NO2) gas in concentrations between 5 and 100 ppm in the mixture with dry air. Response current signal (Igas/Iair) vs. temperature and response vs. gas concentration calibration curves were measured. Best response values were obtained with CoFe2O4 devices between 300 and 400 °C, being 3 and 10 for 100 ppm of CO and 5 ppm of NO2, respectively. The response and recovery times of sensors are between 3 and 30 min. The Fe2O3 and CoFe2O4 sensors with response of 8 or 10 to 5 ppm of NO2 might be of practical applications in the detection of explosives.

► Fe2O3 and CoFe2O4 nanoparticle (NP) arrays as CO and NO2 gas sensing elements.
► Arrays from 1 or 7 NP monolayers were deposited by Langmuir–Blodgett technique.
► Arrays were heat-treated or UV irradiated to remove the insulating surfactant.
► Relative signal change up to 10 obtained with CoFe2O4 devices between 300 and 400 °C.
► Recorded sensing of 5 ppm of NO2 might be applied in the detection of explosives.