A ppb-level formaldehyde gas sensor based on CuO nanocubes prepared using a polyol process

We fabricated and characterized a highly formaldehyde-sensitive gas sensor based on CuO nanocubes. Cu2O nanocubes were synthesized through a wet, facile, and mass-producible polyol process, and oxidized CuO nanocubes were prepared using thermal oxidation under air conditions. The synthesized nanocubes were monodisperse, and the average edge size was about 90 nm and average pore size about 52 nm. We determined the operating temperature of the gas sensors to be 300 °C, considering the proper sensitivity and a rapid response. At this operating temperature, the CuO nanocube gas sensors showed a high HCHO gas response, that is, logarithmic properties in an HCHO gas concentration range of 0.05-3 parts per million (ppm). The gas sensors demonstrated excellent reproducibility (coefficient of variation of 1.17% with 800 parts per million (ppb) at 300 °C) and a very low limit of detection of 6 ppb at 250 °C. Furthermore, among the tested gases that commonly exist in the indoor ambient air, like C6H6, NO2, CO, CO2, NH3, and HCHO, the CuO nanocube gas sensors showed the most strong response to HCHO gas at 300 °C. This investigation therefore indicates that an HCHO gas sensor using CuO nanocubes can be a simple and useful platform for sensing very hazardous indoor formaldehyde gas at several levels of ppb.