Promoting effect of adding carbon nanotubes on sensing characteristics of ZnO hollow sphere-based gas sensors to detect volatile organic compounds

• Highly pure/size-controlled MWCNTs/ZHSs hybrid mixtures were prepared by a simple/efficient ultrasonic-based method.
• All sensing properties of screen printed ZHSs-based sensors in response to VOCs were promoted by adding CNTs.
• Selectivity was strengthened in hybrid sensors by true tuning of temperature and MWCNTs content.
• 0.05, 0.1wt% of MWCNTs were the optimum contents for ethanol and acetone detection, respectively.

Gas sensors based on pure ZnO hollow spheres (ZHSs) and MWCNTs/ZHSs hybrid materials were fabricated. Prepared sensors were examined to detect 320 ppm of target volatile organic compounds including ethanol, methanol, acetone and ether at temperatures ranging from 120 to 380 °C, using direct injection in a closed chamber. Results showed that the addition of CNTs to the ZHSs matrix increased significantly the responses of the hybrid sensors compared to the blank sensor. It was found that the addition of 0.1 wt.% of MWCNTs to the ZHSs matrix increased the response of the resulted sensor to the acetone as much as 8.87 times compared to the blank sensor at the same temperature. It was also found that the addition of MWCNTs to the ZHSs matrix decreased the optimum operating temperatures of the hybrid sensors. In addition, mixing the CNTs with ZHSs makes the hybrid sensors to be selective in response to the target volatile organic compounds. The effect of CNTs on the response and recovery times and saturation limits of the sensors were reported and discussed.