Graphene-wrapped WO3 nanospheres with room-temperature NO2 sensing induced by interface charge transfer

Graphene (GR)-wrapped WO3 nanosphere composite was synthesized by using a facile sol-gel method. The morphology and structural properties of the GR-WO3 nanocomposites were characterized by field-emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. The GR-wrapped WO3 nanospheres composite exhibits p-type gas sensing behavior and the response of GR-WO3 sensor toward NO2 shows a linear increase with an increase in the concentration from 7 to 56 ppm at room temperature. Upon exposure to 56 ppm NO2, its response value becomes 40.8%, but there is no responsiveness for the sensors based on pure WO3 and graphene sensors. The effective charge transfer through chemically bonded interfacial contact between graphene and WO3 nanospheres is proposed to be responsible for the room temperature sensing performance. This work may provide a new insight into the structural design of GR-base nanocomposites and has a potential prospect in the environment monitoring or disease detection of NO2 at room temperature.