A Comparative Study on Performance Improvement of ZnO Nanotubes Based Alcohol Sensor Devices by Pd and rGO Hybridization

This paper concerns a comparative study on the improved alcohol sensing performance of ZnO nanotubes (NTs) based devices via two means: 1) by widely explored catalytic noblemetal (Pd) surface modification (Type 1 device) and 2) relatively less explored technique of surface decoration by reduced graphene oxide (rGO) (Type 2 device). Three types of alcohols viz., methanol, ethanol, and 2-propanol, in the concentration range of 1-800 ppm were considered as the test species for the above-mentioned two types of sensor devices and the results were compared with those of the pristine ZnO NTs based device also. It was found that the sensing performance of the modified devices (both Type 1 and Type 2) was remarkably improved compared to that of its pristine counterpart in terms of response magnitude, response time, and recovery time. The Pd-ZnO NTs hybrid structure offered better sensing performance toward methanol, while the rGO-ZnO NTs hybrid structure offered the same toward ethanol. The underlying sensing mechanism for such improvement of the modified devices toward a specific alcohol species was also elucidated correlating the molecular size of the target species, respective dissociative electron attachment (DEA), and associated band diagram of the hybrid structures.