Metal oxide resistive sensors for carbon dioxide detection

With the development of economy and society and people's pursuit of health and high living quality, more and more attention has been attracted to the detection of carbon dioxide (CO2). Metal oxide semiconductor materials have been widely used in CO2 detection due to their various crystal structure, numerous micro-nano morphologies, simple preparation process, and low cost. This article reviews the sensing mechanism and sensitization methods of CO2 gas sensing materials based on metal oxides. The present works focus on the state of the art of CO2 sensors by utilizing micro-nano hierarchical or assembled structures, doping or loading noble metals and rare earth elements, building heterogeneous structures, and using illumination excitation. The sensitization effect and mechanism are complicated and variable due to the diversity of materials and working conditions. In this paper, the CO2 gas sensing properties of chemical resistive sensors based on various metal oxide semiconductors, such as SnO2, ZnO, TiO2 and BaTiO3, are introduced in detail. Moreover, the CO2 sensing mechanism and sensitization methods of metal oxide materials are discussed in depth, and the advantages and disadvantages of its CO2 sensing application are summarized. Finally, future research focuses are proposed, including reducing the working temperature, improving the long-term stability and cross-sensitive anti-interference ability, demonstrating the sensitization mechanism, and constructing high-energy crystal facets.