Cobalt Iodate Microparticles for Highly Sensitive Acetone Gas Sensor Applications

Introduction

Acetone is well known as a breath gas biomarker of diabetes patient, at concentration level greater than 1.8 ppm in exhaled breath gases¹. Thus, the precise and selective detection of a low concentration (sub-ppm level) of acetone in breath gases containing over 1,000 kinds of gas species can characterize the diagnosis of diabetes. Therefore, reliable acetone gas sensors with highly sensitive and selective acetone response are essential for diagnosis of diabetes. Metal oxide semiconductor (MOS) is one of the most popular acetone gas sensing materials because of their high sensitivity, fast response, and low-cost fabrication². In an effort to improve the selectivity and sensitivity, decoration of catalysts on MOS materials has been suggested. In this study, we used iodine as catalysts on cobalt oxide-based materials and fabricated gas sensors using sol-gel derived cobalt iodate [Co(IO₃)₂] which has a good sensitivity and selectivity toward a low concentration of acetone gas. We also thoroughly characterized the materials using scanning electron microscope (SEM), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA), and polarization-electric field characteristics to figure out the gas sensing mechanism.

Method

Co(IO₃)₂ micro-particles were synthesized by precipitation method from aqueous solutions of Co(CH₃COO)₂·4H₂O and HIO₃ as precursors. For evaluation of effect of iodine doping on cobalt oxide-based materials on gas sensing performance, Co₃O₄ micro-particles were also synthesized by the same method using NH₄OH precursor instead of HIO₃. The obtained precipitates were washed with distilled water and ethanol, followed by drying step. We used the structure of interdigitated (IDT) electrodes for sensor fabrication, described in our previous work³. These powders were dispersed in DI water (1 wt%) and drop-casted on the IDT electrodes on a hot plate at 100 °C. After evaporation of the solvent, the devices were eventually calcined in air at various temperatures. Sensing measurements were done in a gas sensing system varying operating temperatures using a power supply. The gas concentrations were controlled diluting target gases with dry air. We tested gas responses by monitoring changes in resistances of R_g/R_a or R_a/R_g, where R_g is a resistance during exposure to the target gas, and R_a is a resistance in air, respectively.

Results and Conclusions

Figure 1(a) represents gas responses of samples based on Co(IO₃)₂ and Co₃O₄ toward 1.8 ppm of acetone at operating temperature of 250 °C. The gas responses of the Co₃O₄ sample are much smaller than that of Co(IO₃)₂ sample. Accordingly, iodine in a high concentration could play a beneficial role in acetone sensing processes for the sensors. Figure 1(b) shows gas responses for the Co(IO₃)₂ sample annealed at 300 °C toward various gases of 1.8 ppm such as acetone, toluene, NO₂, NH₃, H₂, and H₂S at 250 °C, representing a good selectivity. The optimum operating temperature is found to be 250 °C.

Acknowledgments

J.-S. Park was partially supported by the ATC program (Grant No. 10076984) from MOTIE of the Rep. of Korea.

References

1. C. Deng, J. Zhang, X. Yu, W. Zhang, and X. Zhang, J. Chromatogr. B, 810, 269–275 (2004).

2. 2. Y. Li, M. Zhang, and H. Zhang, Phys. B, 29, 90702 (2020) http://cpb.iphy.ac.cn.

3. S. Nundy et al., Ceram. Int., 46 (2020).

Figure 1