A hybrid graphene-metal oxide sensor for formaldehyde detection at room temperature

The formaldehyde detection is important for protecting human health and controlling environment pollution. Many metal oxide sensors have been developed for the formaldehyde detection in the last decade. The NiO sensor is considered as the most sensitive one, which is able to detect very low concentration of formaldehyde (<1 ppm). But it needs a high operating temperature. Presently, graphene has attracted much attention for sensor applications. Its high surface-to-volume ratio possesses the potential ability to detect the presence of a single interacting molecule and its high carrier mobility ensures low electrical noise and low power consumption. However, pristine graphene is chemically inert and shows weak adsorption of formaldehyde molecules. To obtain stronger adsorption ability, thereby a higher sensitivity, it is necessary to functionalize or pretreat graphene. In this study, we design a new hybrid sensor, in which graphene acts as a highly conductive network and NiO as a sensitive layer for formaldehyde. This hybrid sensor combines the advantages of both materials. Comparing to the pure graphene sensor and the usual NiO sensor, the hybrid sensor demonstrates better sensing performances, such as faster response and recovery, importantly, operating at room temperature. This sensor could be easily integrated with complementary metal oxide semiconductor (CMOS) chip in the future.