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CO2 sensing behavior of calcium doped ZnO thin film: A study to address the cross-sensitivity of CO2 in H2 and CO environment.

CO2, CO, and H2 are the major pollutants in the environment which is primarily generated during the combustion of the organic compounds. Development of a smart sensor that could address the CO2 sensing and its cross sensitivity towards CO and H2 gas is highly advantageous. In this work, an advanced gas sensor is proposed and developed to address the cross-sensitivity of CO2 sensing in CO and H2 environment, which is based on calcium doped ZnO (Ca_ZnO) thin films. The proposed sensors were successfully synthesized using wet chemical synthesis. We have reported that 5 atomic weight % calcium doped ZnO thin film exhibits an efficient sensing performance with a wide range of CO2 gas concentration (75,000 to 5000 ppm) at 350 oC. Additionally, mixed gas sensing characteristics have been carried out for various concentrations of CO (500 to 25 ppm) with CO2 and H2 (500 to 100 ppm) with CO2 gas at 350 C. The response (%) was estimated as 53%, 83% and 74% for 50,000 ppm CO2, 50,000 ppm CO2 + 500 ppm H2, and 50,000 ppm CO2 + CO gas respectively. Furthermore, the enhancement of CO2 sensing was investigated using the Raman spectrum of calcium doped ZnO thin films. Consequently, the cross-sensitivity of pure and mixed gases has been accomplished using principal component analyses (PCA) which shows a distinct cluster formation for each test gas. The proposed gas sensor can be potentially applied to biomass sensing, fuel combustion monitoring, and chemical industries.