Microstructure and sensing properties of CdS-ZnO1-x coatings deposited by liquid plasma spray and treated with hydrogen peroxide solution for nitrogen dioxide detection at room temperature

Metal oxide semiconductor gas sensors usually respond slowly and weakly to target gas at room temperature. In this paper, we report a nitrogen dioxide gas sensor based on porous CdS-ZnO1-x. coatings using a combination of sensitization, surface modification and visible light illumination methods to improve sensing characteristics. Porous CdS-ZnO coatings were deposited by liquid plasma spraying process. Then the coating surface was modified by immersing in a hydrogen peroxide solution and annealing to generate oxygen vacancies and finally obtain CdS-ZnO1-x coatings. Photoluminescence spectroscopy, electron paramagnetic resonance and UV-Vis diffuse reflectance spectrophotometer were utilized to characterize the oxygen vacancies and optical properties of the obtained coatings. The UV-Vis results revealed that the absorption of the obtained coatings was extended to the whole visible light region after the treatment. Nitrogen dioxide gas sensing properties of the CdS-ZnO and CdS-ZnO1-x coatings were measured and compared. The gas sensing results showed that the surface modification (surface oxygen vacancies) can greatly enhanced sensor responses and significantly shortened the response time and recovery time. The sensing mechanism of the obtained CdS-ZnO1-x coatings was discussed in terms of the effect of oxygen vacancies. (C) 2016 Elsevier B.V. All rights reserved.