Ultra-fast real time ethanol sensing behavior and reduction in optical bandgap of the hydrothermally synthesized V2O5/ZnO nanocomposites

• A simple 3-step hydrothermal method has been designed to prepare V 2 O 5 /ZnO nanoparticles/ rods nanocomposites. • Tauc's plot shows that the bandgap of nanocomposite VZ-I and VZ-II lie in between those of V 2 O 5 and ZnO. However, for the VZ-III, it decreased further, showing its comparatively good conductivity. • V 2 O 5 /ZnO nanoparticles/rods nanocomposites based gas sensors exhibit tremendous ethanol sensing properties such as; significant values of sensitivity (reaches >2), lower detection threshold (as low as 5ppm with stable response pattern) for VZ-III nanocomposite and fast real time response speed (less than a second for all nanocomposites). • A schematic gas sensing mechanism has been suggested for the nanocomposites on the basis of energy band diagram of semiconductors. Owing to the significance of metal oxides based nanostructures for the gas sensing applications, this work reports the hybrid V 2 O 5 /ZnO nano-particles/rods nanocomposites (with different V 2 O 5 -ZnO contents ratios; (10:1 (VZ-I), 8:1 (VZ-II) and 6:1 (VZ-III)) prepared via hydrothermal method and characterized for structure, morphology, composition, photoluminescence and optical bandgap by XRD, FESEM, EDX, Photo-Luminescence (PL) and UV–Vis spectroscopy, respectively. Structure of the nanocomposite was reported to consist of both V 2 O 5 and ZnO phases, alongwith V 2 O 3 phase in slight amount at the hetero-structure. Morphology of the nanocomposites is observed as V 2 O 5 nanoparticles (∼10–20 nm), densely anchored into the ZnO nanorods (∼500–700 nm), executing a large surface area. PL spectra indicates that the V 2 O 5 emissions peaks get increased in intensity in nanocomposites but decrease with further increase in the ZnO contents. Tauc’s plot is applied to estimate the optical bandgap variation, showing that the bandgap of the nanocomposites lies within those of V 2 O 5 and ZnO individual metal oxides, However, it lowers below that of V 2 O 5 for the VZ-III nanocomposite. Gas sensors based, on the nanocomposites, were tested for sensitivity in static and dynamic response modes at three distinct temperatures, 100, 140 and 190 °C and the VZ-III nanocomposites exhibits a stable and fast response pattern as compared with the other two nanocomposites and hence declares the VZ-III nanocomposites a promising candidate for gas sensors which is explained on the basis of surface redox reactions and energy band models.