Multi-layered zinc oxide-graphene composite thin films for selective nitrogen dioxide sensing

Abstract

In the present work, selective nitrogen dioxide (NO2) sensing characteristics of multi-layered graphene-zinc oxide (G-ZnO) thin films have been demonstrated at 150 °C. The response% of 5 ppm NO2 was measured to be 894% with response and recovery times estimated to be 150 s and 315 s, respectively. In these composite films, the interaction between graphene and zinc oxide is established through X-ray photoelectron spectroscopy in conjunction with the analyses of photoluminescence spectra. Superior NO2 sensing of these films is due to simultaneous chemiadsorption of molecular oxygen and NO2 gases onto graphene and ZnO surfaces, resulting in an appreciable increase in the depletion layer width and thereby the sensor resistance. The sensor responses for other reducing gases (viz., CO, H2, and i-C4H10) are postulated to be due to their catalytic oxidation on the sensor surface, resulting in a decrease in the sensor resistance upon gas exposure. At lower operating temperature, due to the molecular nature of the chemiadsorbed oxygen, poor catalytic oxidation leads to a far lower sensor response for reducing gases as compared to NO2. For mixed NO2 and reducing gas sensing, we have reported that fast Fourier transformation of the resistance transients of all these gases in conjunction with principal component analyses forms a reasonably distinct cluster and, therefore, could easily be differentiated.

Highly Sensitive Acetone Gas Sensor Based on g-C3N4 Decorated MgFe2O4 Porous Microspheres Composites

“…A modulation model based on the electronic depletion layer [35,36] can explain the gas sensing property. It is well known that MgFe 2 O 4 and g-C 3 N 4 are n-type semiconductors.…”

Multilayered and Chemiresistive Thin and Thick Film Gas Sensors for Air Quality Monitoring

“…Below 150°C, the response to NO 2 is almost negligible. However, with the addition of graphene to ZnO layers, the sensing response significantly increases to 894% [14]. These results are presented in Figure 4.…”

“…The precursor solution was heated at $80°C for complete dissolution and stabilization. Graphene sheet from crystalline graphite was exfoliated by micromechanical cleavage using facile ultrasonication synthesis [14]. For this purpose, 5 mg of graphite powder was mixed in 5 ml of 2-MOE solution.…”

“…This was followed by drying of the substrates in flowing air. Details of deposition process have been reported elsewhere [14]. The multilayered films were annealed at 500°C for 1 h in air.…”

“…Resistance transients of (a) ZnO and (b) ZnO-G multilayer at 150°C. an enormous increase in response is observed on addition of graphene (Reprinted from [14] with the permission of AIP publishing).…”