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.