Facile conversion of zinc hydroxide carbonate to CaO-ZnO for selective CO2 gas detection.

Abstract

Tailored synthesis of heterostructures for low temperature (sub 200\u202f°C) CO2 sensing continues to be a challenging task. The present study demonstrates CO2 sensing characteristics of CaO-ZnO heterostructures achieved by zinc hydroxide carbonate (Zn5(CO3)2(OH)6) conversion to ZnO using Ca(OH)2 at 50\u202f°C. Control samples namely, Zn5(CO3)2(OH)6, Ca(OH)2, ZnO, and CaO integrated microsensors exhibited low sensitivity towards CO2 gas. However, CaO-ZnO heterostructures demonstrated significant sensitivity (26 to 91%) at 150\u202f°C for gas concentration ranging from 100 to 10000\u202fppm, respectively. In this study, zinc hydroxide carbonate sensitized with 25\u202fwt% Ca(OH)2 to form CaO-ZnO heterostructures (25CaZMS) displayed a promising sensitivity (77%) and selectivity (98%) towards 500\u202fppm CO2 gas. Moreover, the selectivity studies were conducted in the presence of 10 commonly found gases and their sensing performance was compared against CO2 gas in dry and humid conditions. The developed CaO-ZnO sensor exhibited faster kinetics in comparison to the control samples. Improved sensing performance observed here is attributed to the low-temperature synthesis route which resulted in a large number of active pores and high surface area morphology. Additionally, the high CO2 adsorption capacity of CaO combined with compatible n-type semiconductors in forming highly dynamic nano-interfaced heterostructure is a promising step towards developing a precise CO2 gas microsensor.