Ultrasensitive ppb-level NO2 gas sensors at room temperature based on SnS2/rGO nanohybrids with P-N transition property and optoelectronic visible light enhancement performance

Nitrogen dioxide (NO2) is an important gas for industrial production, medical treatment and biology. At present, the detection of ultralow concentration (at ppb level) of NO2 under low temperature with other interfering gases is still a great challenge. In this work, we developed nanohybrids of SnS2 and reduced graphene oxide (SnS2/rGO) as gas sensors by a simple one-step hydrothermal method. Especially, the sensors exhibit transitions in the properties of p-type and n-type sensing behavior towards NO2 by adjusting the ratio of graphene to SnS2. Both the two types of sensors demonstrate a remarkable LOD of 5.03ppb, 1.10ppb and sensitivity of 650%, 40% at 1 ppm, respectively. Fast response and strong selectivity are also realized at room temperature. The ability of the sensors to be manipulated by visible light and the influence of light density and wavelength are investigated particularly. Red light (650nm) with 1mW/cm2 can greatly enhance the sensitivity by around five-fold and accelerate the recovery rate greatly, and a complete response and recovery curve with good sensitivity to 10ppb NO2 is realized. Further, ab initio DFT calculations and the band structure of the nanohybrids explain the interaction of the components and the effect of the light-induced carriers on gas sensing behavior.