Graphene is a single layer of carbon atoms with a large surface-to-volume ratio, providing a large capacity gas molecule adsorption and a strong surface sensitivity. Chemical vapor deposition-grown graphene-based NO₂ gas sensors typically have detection limits from 100 parts per billion (ppb) to a few parts per million (ppm), with response times over 1000 s. Numerous methods have been proposed to enhance the NO₂ sensing ability of graphenes. Among them, surface decoration with metal particles and metal-oxide particles has demonstrated the potential to enhance the gas-sensing properties. Here, we show that the NO₂ sensing of graphene can be also enhanced via decoration with monodisperse polymer beads. In dark conditions, the detection limit is improved from 1000 to 45 ppb after the application of polystyrene (PS) beads. With laser illumination, a detection limit of 0.5 ppb is determined. The enhanced gas sensing is due to surface plasmon polaritons excited by interference and charge transfer between the PS beads. This method opens an interesting route for the application of graphene in gas sensing.

Cobalt hydrate and doped binary Co_0.9M_0.1OOH (M = Ni, Mn, Fe) nanorings of 100–300 nm were fabricated in solution through a facile ambient oxidation method. A transformation from Co_0.9Ni_0.1(OH)₂ nanodiscs to hollow Co_0.9Ni_0.1OOH nanorings was observed with prolonged reaction time. Core-shell nanodiscs have elemental segregation with a Co(OH)₂ core and Ni(OH)₂ shell. Co_0.9Ni_0.1OOH nanorings displayed a higher electrochemical capacitance than Mn and Fe doped nanorings materials or materials with disc-like geometries.