Enhanced H₂S gas sensing performance of ZnFe₂O₄/ZnO composite thick films synthesized via hydrothermal method

A hydrothermal method was employed to synthesize pure ZnFe₂O₄ and the composite nanomaterial ZnFe₂O₄/ZnO. The crystal structure, phase purity and particle size were characterized using powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED). Optical properties were studied through UV–visible absorption and FTIR spectroscopy. To explore their potential applications, pure ZnFe₂O₄ and ZnFe₂O₄/ZnO composite nanomaterials were used to fabricate thick-film gas sensors via screen printing. The surface morphology and elemental composition of the thick films were examined using field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray spectroscopy (EDS). The activation energy of both pure and composite nanomaterials was also evaluated. Gas sensing properties were investigated by measuring the sensor response to various probe gases (CO₂, CO, H₂, NH₃, Cl₂, and H₂S) at different operating temperatures. The gas sensing tests revealed that the ZnFe₂O₄/ZnO composite sensor demonstrated superior sensitivity, faster response, and recovery times for 500 ppm H₂S gas at lower operating temperatures compared to pure ZnFe₂O₄. These enhanced properties can be attributed to the unique rough, porous structure of the ZnFe₂O₄/ZnO composite and the heterojunction interactions at the ZnFe₂O₄/ZnO interfaces.