Near Room Temperature Light-Activated WS(2)-Decorated rGO as NO(2) Gas Sensor

The NO(2) response in the range of 200 ppb to 1 ppm of a chemoresistive WS(2)-decorated rGO sensor has been investigated at operating temperatures of 25 °C and 50 °C in dry and humid air (40% RH) under dark and Purple Blue (PB) light conditions (λ = 430 nm). Few-layers WS(2), exfoliated by ball milling and sonication technique, with average dimensions of 200 nm, have been mixed with rGO flakes (average dimension 700 nm) to yield WS(2)-decorated rGO, deposited on Si(3)N(4) substrates, provided with platinum (30 μm gap distance) finger-type electrodes. TEM analysis showed the formation of homogeneous and well-dispersed WS(2) flakes distributed over a thin, continuous and uniform underlying layer of interconnected rGO flakes. XPS and STEM revealed a partial oxidation of WS(2) flakes leading to the formation of 18% amorphous WO(3) over the WS(2) flakes. PB-light irradiation and mild heating of the sensor at 50 °C substantially enhanced the baseline recovery yielding improved adsorption/desorption rates, with detection limit of 400 ppb NO(2) and reproducible gas responses. Cross sensitivity tests with humid air interfering vapor highlighted a negligible influence of water vapor on the NO(2) response. A charge carrier mechanism between WS(2) and rGO is proposed and discussed to explain the overall NO(2) and H(2)O response of the WS(2)–rGO hybrids.