Gas sensing properties of hematite nanoparticles synthesized via different techniques

The synthesis techniques used for metal oxide semiconductors strongly influence their chemical, physical and gas sensing characteristics. In this context, hematite (α-Fe₂O₃) nanoparticles (NPs) were synthesized using two different techniques, namely, sol-gel (named H_SG) and Pechini sol-gel (named H_PSG). The average crystallite size and surface area were 15 nm and 76 m² g^-1 and 20 nm and 57 m² g^-1 for H_PSG and H_SG, respectively. Morphological studies showed that the H_SG material was composed of ellipsoid-shaped particles, while the H_PSG material had peanut-shaped particles with open pores and channels. The comparison between the sensing performances of H_PSG and H_SG toward ethanol indicated H_PSG to be a better sensing material for ethanol detection. The H_PSG sensor exhibited a response of 12 toward 500 ppm ethanol at 250 °C, a fast response time of 5 s and excellent selectivity. The enhanced characteristics were mainly related to the peculiar morphology with a porous nature, which led to more gas adsorption and diffusion. In addition to shape influence, the size of NPs also has an effect on the gas sensing performance. In fact, a decrease in the crystallite size led to an increase in the surface area of the material where the gas molecule-sensing layer interaction took place. The increase in the surface area created more interaction sites, and thus the sensitivity was improved. From these results, the H_PSG sensor can be regarded as a promising candidate for ethanol detection.