Design of long-term stable formaldehyde sensor and its humidity enhanced sensing effect

Developing a long-term stable gaseous formaldehyde (HCHO) sensor is urgent. Titanium dioxide (TiO2) nanorods, an excellent stable oxide, were modified on the Quartz Crystal Microbalance (QCM) sensing platform for HCHO detection. This sensor detects HCHO as low as 50 ppb at normal temperature, and the response time (10 s) and recovery time (13 s) are very short. Besides, its selectivity and short-time repeatability are also satisfactory. Notably, the sensor still maintains the HCHO detection ability after 5 months thanks to the stability of TiO2. In addition, the enthalpy change in the sensing process was extracted by the variable temperature experimental method. Moreover, the hydrate HCHO molecule (i.e. HCHO center dot beta H2O) has a larger molecular weight in real air containing humidity, so we elucidated the molecular formula of hydrate HCHO: the specific range of HCHO center dot beta H2O with a relative humidity of 50-90% is HCHO center dot 2.03 similar to 2.35 H2O.

Automated summary

Developing a long-term stable gaseous formaldehyde (HCHO) sensor is urgent. The modified Titanium dioxide (TiO2) nanorods on the Quartz Crystal Microbalance (QCM) sensing platform demonstrate excellent HCHO detection capabilities with a low detection limit of 50 ppb at normal temperature. The sensor also exhibits short response and recovery times of 10 s and 13 s, respectively, and satisfactory selectivity and short-term repeatability. Furthermore, the molecular formula of hydrate HCHO (HCHO•βH2O) in real air containing humidity is elucidated as HCHO•2.03-2.35H2O within a relative humidity range of 50-90%.