Growth concentration effect on oxygen vacancy induced band gap narrowing and optical CO gas sensing properties of ZnO nanorods

Abstract

Band gap energy and surface defect on the nanostructure play an important role especially in determining the performance and properties of the optical based gas sensor. In this report, ZnO nanorods (ZNRs) with various growth concentrations were successfully synthesized using a facile wet chemical approach. The gas sensing performance of the ZNRs samples with different concentrations were tested toward the highly hazardous carbon monoxide (CO) gas at a concentration of 10 ppm operated at room temperature. It was found that the 40 mM ZNRs sample exhibited the highest response coupled with the shortest response time (123.3 ± 1.3 s) and recovery time (7.7 ± 0.3 s). The high response and accelerated sensing reaction were attributed to the band gap narrowing of the 40 mM ZNRs induced by the increase in oxygen vacancy related defect states, and it is directly proportional to the CO gas sensing activity. These defects acted as the oxygen trap sites which will promote the oxygen adsorption on the surface of ZNRs and enhanced its gas sensing capability. The ZNRs reported herein which exhibits a high sensitivity, fast and reversible response with rapid recovery have great potential to be used in toxic gas sensing applications at room temperature.