Synthesis, Characterization, and Sensing Performance Investigation of Nickel Ferrite Nanoparticles for Ammonia Detection

In this article, NiFe2O4 nanocrystals were prepared through the co-precipitation method. The two variables in the nickel ferrite synthesis were the temperature gradient of reaching the heat treatment temperature and the pure oxygen pressure of the heat treatment atmosphere. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray fluorescence (XRF) spectroscopy experiments were used to verify the formation of the ferrite phases, the formation of the ferrite nanostructure phase, the proper morphology of the particles, and the accuracy of the atomic ratios of the ferrite product, respectively. NiFe2O4 nanocrystals as ammonia gas sensors were evaluated at 65 °C. A laboratory device with the capability of temperature and humidity control and with the capacity of 5 L was used to test the susceptibility of nanosensors. This device was equipped with a temperature control heater, and then sensors were placed on this device. A gas injection chamber and an electronic interface board were also used. After that, nanosensors' data were transmitted to a computer system and were analyzed by LabVIEW software. In our study, we found that both the variables in the nickel ferrite synthesis have a role in resistivity variations in sensors. The effect of the atmospheric oxygen pressure on the heat treatment was approximately equal to the temperature gradient reaching the temperature of the heat treatment. In addition, the synthesized sensor with a 10 °C/s temperature gradient and an oxygen atmosphere of 1.5 psi was better than the other eight nanosensors. This sensor is determined as the superior nanosensor, and the relationship between gas concentration and resistivity in this nanosensor is reported.