Room-Temperature Carbon Dioxide Gas Sensor Based on Co-Ferrite Nanoparticles

The development of carbon dioxide (CO₂) sensors is essential for both environmental and indoor air monitoring applications. Here, we investigate the CO₂-sensing performance of cobalt ferrite (CoFe₂O₄) nanoparticles (NPs) at room temperature under relative humidity (RH) conditions. The NPs exhibit a phase-pure spinel CoFe₂O₄ structure with an average particle size of approximately 6 nm. The fabricated sensors demonstrate high CO₂ sensitivity, showing a nearly linear response over concentrations ranging from 250 to 4000 ppm, with stable reproducibility over repeated exposure cycles and prolonged operation at 30% RH. The sensor demonstrates a broad and practically relevant concentration detection range, exhibiting high sensor signals and reliable response/recovery for real-life applications. Interestingly, higher humidity levels (50% RH) alter the sensing mechanism due to the introduction of parallel conduction pathways promoted by increased water coverage on the surface of the NPs. Furthermore, an increase in crystallite size to 60 nm results in diminished CO₂ signal, underscoring the critical role of nanosized particles in enhancing gas diffusion and active site availability. This work therefore shows that CoFe₂O₄ NPs correspond to a promising material platform for room-temperature CO₂ detection, with humidity and particle size having a strong influence on their sensing performance.