High-Selectivity Laminated Gas Sensor Based on Characteristic Peak under Temperature Modulation.

Aiming at the bottleneck problem of insufficient selectivity of metal oxide gas sensors, a reliable scheme to improve selectivity is proposed, that is, a laminated sensor structure of a gas-sensitive membrane plus catalytic membrane combined with the temperature modulation technology. It is presented as a highly selective ethanol sensor as an example for verification. The laminated gas sensor is made of Sr@SnO2 as the gas-sensing membrane and ZSM-5 as the catalytic membrane by the microelectro mechanical system. The results indicate that in temperature modulation mode, the Sr@SnO2/ZSM-5-laminated sensor has good resistance gas-sensing response to most different types of gases but only shows a characteristic peak on the time-resistance and temperature-resistance curves of ethanol gas response. By defining and calculating this characteristic peak, the selectivity of ethanol gas response signal is improved. The Sr@SnO2/ZSM-5 sensor also exhibits high sensitivity to ethanol gas at the parts per billion level, fast response/recovery time in seconds, excellent anti-interference, and stability, indicating the reliability and practicality of this highly selective scheme. This scheme is of great significance for the study of high selectivity of a metal oxide gas sensor and promotes its wide application.

Cross-Interference of VOCs in SnO2-Based NO Sensors.

In this work, we studied the influence of cross-interference effects between VOCs and NO on the performance of SnO2 and Pt-SnO2-based gas sensors. Sensing films were fabricated by screen printing. The results show that the response of the SnO2 sensors to NO under air is higher than that of Pt-SnO2, but the response to VOCs is lower than that of Pt-SnO2. The Pt-SnO2 sensor was significantly more responsive to VOCs in the NO background than in air. In the traditional single-component gas test, the pure SnO2 sensor showed good selectivity to VOCs and NO at 300 °C and 150 °C, respectively. Loading noble metal Pt improved the sensitivity to VOCs at high temperature, but also significantly increased the interference to NO sensitivity at low temperature. The explanation for this phenomenon is that the noble metal Pt can catalyze the reaction between NO and VOCs to generate more O-, which further promotes the adsorption of VOCs. Therefore, selectivity cannot be simply determined by single-component gas testing alone. Mutual interference between mixed gases needs to be taken into account.

TiO2/(K,Na)NbO3 Nanocomposite for Boosting Humidity-Sensing Performances.

Nanomaterials of TiO2, (K0.5Na0.5)NbO3, and the TiO2/(K0.5Na0.5)NbO3 nanocomposite were successfully synthesized by a hydrothermal method. Impedance-type humidity sensors were fabricated based on these materials. Our results reveal that the impedance of the TiO2/(K0.5Na0.5)NbO3 sensor changes by 5 orders of magnitude with an ultrahigh sensing response of Sf = 166 470 recorded at 100 Hz in the tested relative humidity (RH) range of 12-94%. This value is almost 2 and 4 orders of magnitude larger than that of the (K0.5Na0.5)NbO3 and TiO2 sensors, respectively. Interestingly, satisfactory response/recovery time (25/38 s, within 5 min), very small hysteresis (<5%), excellent stability, and good repeatability were also achieved in the TiO2/(K0.5Na0.5)NbO3 sensor. The improved sensing properties are ascribed to the synergistic effect of TiO2/(K0.5Na0.5)NbO3 heterojunction, which contributes the impedance that is susceptible to environmental humidity. This work underscores that it is a facile way to boost humidity-sensing performance by constructing proper nanocomposites.