Enhancement of gas sensing properties by the functionalization of ZnO-branched SnO₂ nanowires with Cr₂O₃ nanoparticles

Complex metal oxides such as functionalized branched nanowires (NWs) are a new category of nanocomposites with unique properties for gas sensing applications. In the present work, we studied the gas sensing properties of Cr₂O₃-functionalized ZnO-branched SnO₂ NWs, inspired by their high surface area and numerous resistive points. These NWs were studied and compared with pristine SnO₂ NWs and ZnO-branched SnO₂ NWs. To prepare the functionalized NWs, ZnO-branched SnO₂ NWs were sputter-coated with a Cr layer and then annealed at 500 °C to produce isolated Cr₂O₃ NPs on the ZnO branches. Results of X-ray diffraction, scanning electron microscopy, and lattice-resolved transmission electron microscopy collectively showed that Cr₂O₃-functionalized ZnO-branched SnO₂ NWs were successfully formed. Cr₂O₃ functionalization was found to greatly improve the sensors’ response to NO₂ gas. Furthermore, the sensors’ good selectivity was demonstrated by testing them in the presence of various interfering gases. The underlying gas sensing mechanisms are discussed herein in detail. We believe that the Cr₂O₃-functionalized ZnO-branched SnO₂ NWs reported herein are promising sensors for the highly sensitive and selective detection of NO₂ gas.