Structural, optical and gas sensing studies for high-performance chlorine gas sensor based on hydrothermally synthesized CuFe₂O₄/CuO nanocomposite

Gas sensors are essential for environmental safety, industrial process monitoring, and public health, particularly for detecting hazardous gases like chlorine (Cl₂). In this work, a CuFe₂O₄/CuO composite nanomaterial was synthesized through a straightforward two-step hydrothermal process followed by thermal treatment and its effectiveness as a highly sensitive and selective Cl₂ gas sensor was thoroughly investigated. X-ray diffraction (XRD) analysis verified the successful formation of pure-phase CuFe₂O₄ and its composite, exhibiting an average crystallite size of 57.12 nm and 35.6 nm, respectively. Porous nanostructures with average particle size 48.98 nm were observed using high-resolution transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FESEM). UV–Visible spectroscopy showed a reduced band gap of 1.7 eV for the composite, while FTIR analysis confirmed characteristic metal–oxygen vibrational modes and the successful incorporation of CuO. Thick films of pure CuFe₂O₄ and CuFe₂O₄/CuO were fabricated via screen printing to evaluate their gas sensing performance. Electrical characterization demonstrated improved conductivity and lower activation energy in the composite, enhancing charge transfer during gas exposure. The CuFe₂O₄/CuO sensor responded strongly, reaching a value of 91 % to 300 ppm Cl₂ at a relatively low operating temperature of 150 °C significantly better than the pure CuFe₂O₄ sensor, which required 300 °C for optimal performance. Furthermore, the composite sensor showed a rapid response time of 3.6 s and a recovery time of 92.7 s and low detection limit (LoD) of 87.4 ppm and good stability. These results demonstrate the potential of CuFe₂O₄/CuO nanocomposites for developing high-performance, low-temperature Cl₂ gas sensors.