Dual Activation and Photocatalyst-Induced Selective Detection in Defect Tuned Pd–ZnO Thin Films for Low ppm Detection of CH and CO

The selectivity of CO and CH4 remains a hurdle to researchers working on metal-oxide-based sensors, as the sensing mechanism is analogous for both gases. With this objective, an attempt has been made to realize selective sensing of CH4 (up to 1 ppm) and CO (up to 1 ppm) by introducing a selective photocatalyst layer (Zn5(OH)8Cl2.H2O) on Pd–ZnO. It has been noticed that the incorporation of a photocatalytic layer is found to be highly efficacious in providing the sensor with a strong absorption reaction and propelling the surface conversion kinetics. The role of dual activation and photocatalytic activity in selectivity along with tunability is also explored in this work. The dual activation incorporates the benefits of both temperature and optical excitation on metal-oxide-based sensors, highlighting the innumerable advantages and nullifying the disadvantages of both methods. Tunable and selective sensing with a response time/recovery time of 40 s is explicated. The method for improving the sensing performance of Pd–ZnO–photocatalyst-based nanostructures in terms of repeatability and cross sensitivity with respect to 1 ppm of CO, 1 ppm of CH4, 1 ppm of NH3, 250 ppm of CO, and 40% of O2 is discoursed. It has been observed that the sensor with a sensitivity of 23%/ppm for CH4 and 93%/ppm for CO with a minimum baseline drift of less than 3% is achieved. The long-term stability and repeatability of dual-activated sensors are also verified, and less than 3% change has been noticed. The work can be extended for the selectivity of other metal oxides as well.