Enhanced room temperature sensitivity of Ag-CuO nanobrick/reduced graphene oxide composite for NO2

Pure and Ag-CuO nanostructures with different Ag content (Cu_1-xAg_xO, x = 0, 0.02, 0.05, 0.08 and 0.12) were synthesized via hydrothermal method and their composite films with reduced graphene oxide (rGO) were fabricated by drop casting method for the gas sensing measurements. Different techniques like XRD, FESEM, TEM, BET, Raman and XPS were used for the characterization of the samples. FESEM and TEM results depicted the formation of nanobrick like morphology for pure and Ag-CuO. Moreover, FESEM elemental mapping of Ag-CuO samples showed the homogeneous distribution of Cu, Ag and O in all the samples. The experimental results of the NO₂ gas sensing at different operating temperatures ranging from 22 to 100 °C revealed that Ag-CuO/rGO sensor with 5 at% Ag exhibited maximum response. At room temperature (RT) of ∼22 °C, Ag-CuO/rGO (5 at% Ag) showed 67.2% response to 20 ppm NO₂ which is 1.9 times of the CuO/rGO sensor. Thus the amount of Ag content in the CuO/rGO sensor influence the NO₂ gas sensing response. In addition, Ag-CuO/rGO (5 at% Ag) possessed excellent response time of 35 s for 20 ppm NO₂, good repeatability, stability and selectivity for NO₂ gas. Interestingly, Ag-CuO/rGO (5 at% Ag) sensor showed maximum response at an intermediate relative humidity (∼52%RH). Moreover, the sensing mechanism for improved sensing performances of the Ag-CuO/rGO sensor was discussed in this paper. The present work suggests that the Ag-CuO/rGO composite is a potential material for detection of NO₂ at RT.