1. Introduction
Humans emit large amounts of carbon dioxide (CO2) mainly by burning fossil fuels such as coal, natural gas, and oil for energy production, transportation, as well as for industrial processes. The increase in these CO2 emissions causes the sun’s heat to be trapped in the atmosphere, leading to the climate crisis.
The current outdoor concentration of CO2 is around 400 ppm, but indoor concentrations can rise to between 2000 and 3000 ppm. Moreover, although this gas is not as harmful to humans as carbon monoxide (CO), levels of CO2 between 800 and 2000 ppm can cause headaches, tiredness, and loss of concentration.
Performing this experiment using rapid and low-cost techniques allows for the development of fast and economical sensors. The FR-4 substrates and compounds used are very affordable in terms of cost. Thanks to the UV led activation, these sensors do not require heating methods, therefore they can be easily used at room temperature.
2. Materials and Methods
The starting material was nanoparticles of Tin(IV) oxide with particle size below 100 nm, and Zinc oxide, Iron(III) oxide, and Copper(II) oxide with particle size below 50 nm, all supplied by Sigma–Aldrich (St. Louis, MO, USA).
The sensitive layers were formed creating dispersions of the metal oxide NPs, which were prepared in deionized water at a concentration of 2.5 mg/mL. They were deposited by drop-casting [
1] on FR-4 substrates with interdigitated electrodes.
3. Discussion
In this project, the best responses were achieved with the SnO
2 and ZnO sensors, whereas the responses were poor when using Fe
2O
3 and CuO oxides. As shown in
Figure 1, the response was significantly better in humid air, with a response almost twice as good as that obtained in dry air.
In this experiment, measurements were conducted to detect other gases such as CO or methane, but the best sensitivity values were obtained for CO2 gas.
The sensor response is calculated as the relative resistance change between the resistance measured in air (
) and the resistance measured when the gas is present (
).
Author Contributions
Conceptualization and methodology, I.S. and J.P.S.; validation, I.S. and J.P.S.; formal analysis, J.G.; investigation, I.S. and J.G.; resources, I.S.; data curation J.G.; writing—original draft preparation, J.G.; writing—review and editing, I.S., J.G. and J.P.S.; visualization, I.S. and J.G.; supervision, I.S. and J.P.S. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Data are contained within the article.
Acknowledgments
The authors are grateful to the Spanish Ministry of Science, Innovation and Universities for supporting their research under the Smart-AirQ project (TED2021-131114B-C22) founded by MCIN/AEI/10.13039/501100011033 and by European Union “NextGenerationEU”/PRTR.
Conflicts of Interest
The authors declare no conflict of interest.
Reference
- Santos, J.; Sanchez-Vicente, C.; Azabal, A.; Ruiz-Valdepenas, S.; Lozano, J.; Sayago, I.; Sanjurjo, J. Automation and optimization device for the fabrication of sensors with nanomaterials. In Proceedings of the 2021 13th Spanish Conference on Electron Devices (CDE), Sevilla, Spain, 9–11 June 2021; pp. 129–131. [Google Scholar]
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