Sensitive and selective NiFe₂O₄-based gas sensor for hazardous hydrogen sulfide (H₂S) monitoring

Hydrogen sulfide (H₂S) is a hazardous environmental pollutant that poses significant health risks, demanding the development of high-performance monitoring systems. This work reports the successful hydrothermal synthesis of inverse spinel nickel ferrite NiFe₂O₄ nanomaterials for use as a chemiresistive gas sensor. Structural and morphological characterizations, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and photoluminescence (PL), confirmed the formation of a cubic spinel phase with a mesoporous architecture. Brunauer-Emmett-Teller (BET) analysis revealed a specific surface area of 58 m² g^-1, which provides an abundance of active sites for gas-solid interactions. X-ray photoelectron spectroscopy (XPS) analysis elucidated the sensing mechanism, showing the appearance of sulfur species and shifts in Ni 2p peaks, confirming the strong interaction between H₂S and the ferrite surface. The sensing performance was systematically evaluated, showing a remarkable response of 90 toward a low H₂S concentration of 5 ppm at an optimal operating temperature of 200 °C. This detection capability is well below the Threshold Limit Value (10 ppm). The sensor exhibited a quick response time of 10 seconds, exceptional selectivity, and high stability, demonstrated by a low relative standard deviation (RSD of 1.12%). Although humidity caused competitive adsorption effects, the sensor maintained a strong and measurable signal. These results indicate that NiFe₂O₄ is an excellent candidate for sensitive and practical H₂S detection applications.