High-energy (110) and twin-defect (20−2) faceted CuO nanosheets enable ultrasensitive trace formaldehyde sensing

The dynamic reaction process of HCHO, encompassing its adsorption onto the surface of CuO nanosheets, subsequent oxidation to formic acid, and further oxidation to carbon dioxide, was elucidated using in-situ infrared spectroscopy and Gibbs free energy calculations. • Surface-induced preparation facilitates the formation of high-energy (110) crystal planes and (20−2) twin defects in CuO nanosheets, which synergistically enhance their performance for ultra-sensitive formaldehyde detection. • The CuO nanosheet sensor exhibits an extremely low detection limit of 0.1 ppb, along with rapid response and recovery times, enabling long-term and continuous detection. Long-term exposure to an environment above the formaldehyde threshold poses a serious threat to human health. In this study, by adjusting the concentration of the surfactant polyvinylpyrrolidone, CuO nanosheets with high-energy crystal planes (110, 20−2) twinning defect structures were successfully prepared for the first time. Through operando infrared and theoretical calculation of Gibbs free energy and adsorption energy, the dynamic process of HCHO adsorption on the surface of CuO, oxidation to formic acid and ultimately to carbon dioxide was revealed for the first time. The results of the gas sensitivity test show that the response value of the CP-4 sensor to formaldehyde reaches 129.95 (5 ppm) at the low operating temperature (100 °C), with a detection limit as low as 8.4 ppb. The response/recovery time were 6 s/14 s. This sensor demonstrated excellent stability during 50 cycles and 90 days of continuous operation. Its outstanding performance stems from the fact that high-energy crystal planes increase the active sites for oxygen adsorption, and twinning defects accelerate electron transfer. The examination system based on the STM-32 platform verified the feasibility of practical application. This study provides a new strategy for optimizing the performance of CuO-based HCHO sensors, which has significant guiding significance for the development of high-performance semiconductor gas sensors. Download: Download high-res image (131KB) Download: Download full-size image