Effect of Various Heat Treatment Conditions on Nickel Ferrite Nanoparticles and Investigating its Sensitivity to Formaldehyde

In this study, NiFe2O4 nanoparticles, with respecting two variables, were prepared through co-precipitation. These two variables are the temperature gradient reaching the temperature of the heat treatment of 500 °C at 10°C/sec, 35°C/sec and 60 °C/sec and the pure oxygen pressure as the heat treatment atmosphere for one hour, at 0.5 psi, 1 psi, and 1.5 psi. So, we found 9 samples, that the sample with the best sensitivity response to formaldehyde (sample with 10°C/sec heat treatment and 1 psi pure oxygen pressure) was characterized. X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM) and X-ray fluorescence (XRF) experiments were used to study the structure of these nanoparticles. X-ray diffraction experiment has verified formation of nickel ferrite phases. Furthermore, scanning electron microscopy and transition electron microscopy experiments confirmed that the ferrite was indeed a nano-structure. Finally, NiFe2O4 formula ratio was derived by X-ray fluorescence experiment. The sensitivity property of NiFe2O4 nanoparticles for formaldehyde gas detection was studied at 100 °C. For testing the sensitivity of nanosensors, a laboratory 5 liters system was used with temperature and humidity control. This system equipped with a temperature control heater for heating sensors. Relationship between gas concentration (from 20 ppm to 200 ppm) and resistance change of nano sensor with the best response to formaldehyde was investigated.