Porous SnO2 nanospheres coated with reduced graphene oxide for formaldehyde gas sensor: Synthesis, performance and mechanism

Mesoporous SnO 2 nanospheres are synthesized by template-free solvothermal method, and then reduced graphene oxide (rGO) nanosheets are anchored on SnO 2 nanospheres (SnO 2 @rGO nanocomposites) by hydrothermal method. The gas-sensing results indicate that rGO nanosheets greatly affect the formaldehyde (HCHO) gas-sensing properties, which the response to 100 ppm HCHO gas increases with the rGO content and reach the maximum of 113.56 at 190 °C for SnO 2 @0.5%rGO sensor. Owing to the huge surface area and conductivity, rGO nanosheets absorb more oxygen molecules and extract electrons from SnO 2 nanospheres, leading to the thicker electron depletion layer of SnO 2 nanospheres. Furthermore, p-n heterojunctions at the interface of rGO nanosheets and SnO 2 nanospheres further increase the thickness of electron depletion layer. However, SnO 2 @0.8%rGO sensor presents the lower response for the new conductive pathways between the surface rGO nanosheets due to the excess of rGO content. Graphical abstract