Development and evaluation of ZnO and ZnO/MWCNT composite as CO2 gas sensors

Abstract

Sensing devices have currently become essential to monitor CO2 concentrations in human exhalation and the environment. These devices play a crucial role in identifying acceptable limits and ventilation rates in the workplace, thus optimizing the return to classrooms, laboratories, and offices during the global coronavirus pandemic (SARS-CoV-2). The purpose of this study is to obtain a composite material by combining zinc oxide (ZnO) and multi-walled carbon nanotubes (MWCNTs) and investigate its structural and sensing properties. Pure ZnO nanostructures were synthesized by homogeneous precipitation assisted by ultrasound irradiation, while MWCNTs were prepared by spray pyrolysis at 700 °C. Subsequently, the ZnO/MWCNT composite was synthesized by wet chemical method and tested for CO2 detection at different concentrations from 5 to 500 ppm. The hexagonal wurtzite phase of ZnO and ZnO/MWCNT composite was evaluated by X-ray diffraction (XRD) measurements at room temperature. Additionally, a scanning electron microscopy (SEM) analysis showed a rod-like morphology in the ZnO structures and agglomerated prisms in the ZnO/MWCNT composite. Finally, the CO2 detection properties analyzed in this study were sensing response, response time, recovery time, repeatability, and stability in both samples.