ZnAl₂O₄ nanoparticles were synthesized employing a colloidal method. The oxide powders were obtained at 300 °C, and their crystalline phase was corroborated by X-ray diffraction. The composition and chemical structure of the ZnAl₂O₄ was carried out by X-ray and photoelectron spectroscopy (XPS). The optical properties were studied by UV-vis spectroscopy, confirming that the ZnAl₂O₄ nanoparticles had a direct transition with bandgap energy of 3.2 eV. The oxide’s microstructures were microbars of ~18.2 nm in size (on average), as analyzed by scanning (SEM) and transmission (TEM) electron microscopies. Dynamic and stationary gas detection tests were performed in controlled propane atmospheres, obtaining variations concerning the concentration of the test gas and the operating temperature. The optimum temperatures for detecting propane concentrations were 200 and 300 °C. In the static test results, the ZnAl₂O₄ showed increases in propane response since changes in the material’s electrical conductance were recorded (conductance = 1/electrical resistance, Ω). The increases were ~2.8 at 200 °C and ~7.8 at 300 °C. The yield shown by the ZnAl₂O₄ nanoparticles for detecting propane concentrations was optimal compared to other similar oxides categorized as potential gas sensors.

We implemented a simple and inexpensive aqueous sol-gel process to synthesize ZnAl₂O₄ nanoparticles to study its potential application as a gas sensor. Compared to traditional ceramic methods, the synthesis was conducted at lower temperatures and reaction times (5 h from 200 °C). The crystalline evolution of the oxide was investigated. The effect of the calcination temperature (200–1000 °C) on the crystallites’ size (16–29 nm) and the ZnAl₂O₄ powder’s surface morphology was also analyzed. Measurements confirmed the formation of bar-shaped granules (~0.35 μm) made up of nanoparticles (~23 nm). The surface area of the powders was 60 m²/g. Pellets were made from the powders and tested in sensing carbon monoxide and propane gases, showing a high sensitivity to such gases. The sensor’s response increased with increasing temperature (25–300 °C) and gas concentration (0–300 ppm). The oxide showed a higher response in propane than in carbon monoxide. We concluded that the ZnAl₂O₄ is a good candidate for gas sensing applications.

In this work, powders of NiSb₂O₆ were synthesized using a simple and economical microwave-assisted wet chemistry method, and calcined at 700, 800, and 900 °C. It was identified through X-ray diffraction that the oxide is a nanomaterial with a trirutile-type structure and space group P4₂/mnm (136). UV–Vis spectroscopy measurements showed that the bandgap values were at ~3.10, ~3.14, and ~3.23 eV at 700, 800, and 900 °C, respectively. Using scanning electron microscopy (SEM), irregularly shaped polyhedral microstructures with a size of ~154.78 nm were observed on the entire material’s surface. The particle size was estimated to average ~92.30 nm at the calcination temperature of 900 °C. Sensing tests in static atmospheres containing 300 ppm of CO at 300 °C showed a maximum sensitivity of ~72.67. On the other hand, in dynamic atmospheres at different CO flows and at an operating temperature of 200 °C, changes with time in electrical resistance were recorded, showing a high response, stability, and repeatability, and good sensor efficiency during several operation cycles. The response times were ~2.77 and ~2.10 min to 150 and 200 cm³/min of CO, respectively. Dynamic tests in propane (C₃H₈) atmospheres revealed that the material improved its response in alternating current signals at two different frequencies (0.1 and 1 kHz). It was also observed that at 360 °C, the ability to detect propane flows increased considerably. As in the case of CO, NiSb₂O₆’s response in propane atmospheres showed very good thermal stability, efficiency, a high capacity to detect C₃H₈, and short response and recovery times at both frequencies. Considering the great performance in propane flows, a sensor prototype was developed that modulates the electrical signals at 360 °C, verifying the excellent functionality of NiSb₂O₆.