Functionalized Carbon Nanotubes Enabled Flexible and Scalable Co2 Sensors

Abstract

The demand for CO2 detection steadily increases mainly due to the greenhouse effect caused by CO2 emission, which significantly impacts the environment. Among different promising candidates, carbon-based (i.e., graphene, carbon nanotubes, carbon nanoparticles, etc.) composites have been widely studied due to their exceptional mechanical, electrical, and thermal properties. Besides, carbon-based composites offer high strength-to-weight ratios, excellent conductivity, and superior thermal stability, making them ideal materials for various industrial applications. Despite tremendous efforts to develop CO2 sensors, obtaining a well-dispersed system using those materials remains challenging to achieve an affordable and easy-to-use sensor.  In this work, we have demonstrated a low-cost and effective chemiresistive CO2 sensor based on the composite of functionalized carbon nanotubes (f-CNTs) with polyethyleneimine (PEI). With the modification of pyrene and chlorosulfonic acid, the resultant f-CNTs have outstanding dispersibility in PEI, which is mainly attributed to the non-covalent bonds between CNT and pyrene and the interaction between the amine and sulfonate groups. The rheology of the f-CNT/PEI composites has been thoroughly studied, which tremendously influences the screen-printing quality. The resulting sensor shows excellent selectivity and sensitivity, which can respond to the CO2 concentration in a wide range of 300 - 5000 ppm. The effects of ink dilution and humidity of the environment on the sensor performance have also been further explored. More importantly, the working mechanism has been proposed, and we hope it can provide insight and a new pathway for future sensor design.

Keywords: Carbon nanotubes, carbon dioxide sensors, polyethyleneimine, screen printing, Printed electronics