Influence of rGO Cladding in Improving the Sensitivity and Selectivity of ZnO Nanoflowers-Based Alcohol Sensor

Development of ultra-sensitive and selective 2-propanol sensor employing hybrid structure of reduced graphene oxide (rGO) and 3-D ZnO nanoflowers (NFs) is reported in this paper. The 3-D ZnO NFs were synthesized on n-Si wafer, using liquid phase deposition technique, while a dip coating technique was adopted for the deposition of rGO, in the form of discrete claddings, on the ZnO NFs layer. The detailed morphological (field emission scanning electron microscopy) and structural (Raman and XPS) characterizations were carried out to compare the structural and morphological properties of pristine ZnO NFs and rGO-ZnO NFs hybrid structure. The sensing properties of ZnO NFs and rGO-ZnO NFs devices were investigated toward different alcohol vapors (2-propanol, ethanol, and methanol) in the concentration range of 0.5-700 ppm at 100 °C-275 °C. The rGO-ZnO NFs 3-D hybrid device offered ultra-high sensitivity (645% response magnitude at 700 ppm) toward 2-propanol at ~160 °C. In addition, the same sensor also offered excellent selectivity against interfering neighbors (i.e., ethanol, methanol, acetone, and benzene). The underlying mechanism for such experimental findings has been discussed with the properties of rGO-ZnO hybrid junction and respective band bending in air and target species.