Material dependent and temperature driven adsorption switching (p- to n-type) using CNT/ZnO composite-based chemiresistive methanol gas sensor

The present study correlates two simultaneous as well as significant observations coming out from a single sensing prototype concerning the detection of volatile organic compounds (VOCs) by a carbonaceous material based sensor. We have developed a composite based chemiresistive sensor utilizing two different components (carbon nanotube (CNT) and zinc oxide (ZnO)). This is reflected in a unique adsorption switching phenomena followed by a 'p- to n-' type transition characteristics above a certain operating temperature (150 degrees C) in the VOC detection process. Noticeably, by the virtue of adsorption switching, the CNT/ZnO composite is able to operate as a dual mode sensor, in which CNT dominates in low temperature region (<= 150 degrees C) and ZnO at high temperature region (>150 degrees C) with a realistic detection ability. The highly reproducible sensors (29 prototypes) are selective towards methanol (Response, R similar to 73 +/- 3 %) and shows 8-fold enhancement in response value compared to neighbouring VOC i.e., ethanol at an operating temperature of 150 degrees C with a very low bias voltage of 10 mV. Finally, the adsorption switching phenomena (physisorption to chemisorption) has been explained by Fourier Transform Infrared Spectroscopy (FTIR) study and activation energy values along with 'p- to n-' type transition is compared qualitatively with a typical full wave rectification process.

Automated summary

The study presents a composite chemiresistive sensor utilizing carbon nanotubes and zinc oxide for detecting VOCs, demonstrating unique adsorption switching phenomena and dual-mode sensor capabilities. The sensor shows selectivity towards methanol with high response values, making it a highly reproducible and high-quality sensor.