Microwave-Assisted Synthesis of Graphene-SnO Nanocomposites and Their Applications in Gas Sensors.

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