Microwave-Assisted Synthesis of Graphene–SnO2 Nanocomposites and Their Applications in Gas Sensors

We obtained extremely high and selective sensitivity to NO 2 gas by fabricating graphene–SnO 2 nanocomposites using a commercial microwave oven. Structural characterization revealed that the products corresponded to agglomerated structures of graphene and SnO 2 particles, with small secondary SnO x ( x ≤ 2) nanoparticles deposited on the surfaces. The overall oxygen atomic ratio was decreased with the appearance of an SnO x ( x < 2) phase. By the microwave treatment of graphene–SnO 2 nanocomposites, with the graphene promoting efficient transport of the microwave energy, evaporation and redeposition of SnO x nanoparticles were facilitated. The graphene–SnO 2 nanocomposites exhibited a high sensor response of 24.7 for 1 ppm of NO 2 gas, at an optimized temperature of 150 °C. The graphene–SnO 2 nanocomposites were selectively sensitive to NO 2 gas, in comparison with SO 2, NH 3, and ethanol gases. We suggest that the generation of SnO x nanoparticles and the SnO x phase in the matrix results in the formation of SnO 2 /SnO 2 homojunctions, SnO 2 /SnO x ( x < 2) heterojunctions, and SnO 2 /graphene heterojunctions, which are responsible for the excellent sensitivity of the graphene–SnO 2 nanocomposites to NO 2 gas. In addition, the generation of surface Sn interstitial defects is also partly responsible for the excellent NO 2 sensing performance observed in this study.