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

## TL;DR

This paper presents a CO2 sensor using cobalt ferrite nanoparticles that works at room temperature and is effective for environmental and indoor air monitoring.

## Contribution

The study introduces a novel CO2 sensing material using CoFe2O4 nanoparticles and explores the effects of humidity and particle size on sensor performance.

## Key findings

- CoFe2O4 nanoparticles show high CO2 sensitivity with a linear response from 250 to 4000 ppm at room temperature.
- Higher humidity levels alter the sensing mechanism by introducing parallel conduction pathways.
- Larger nanoparticle size reduces CO2 sensing performance, highlighting the importance of nanoscale particles.

## Abstract

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.