Light-Excited Ag-Doped TiO(2)−CoFe(2)O(4) Heterojunction Applied to Toluene Gas Detection

(1) Background: Toluene gas is widely used in indoor decoration and industrial production, and it not only pollutes the environment but also poses serious health risks. (2) Methods: In this work, TiO(2)−CoFe(2)O(4)−Ag quaternary composite gas-sensing material was prepared using a hydrothermal method to detect toluene. (3) Results: The recombination of electron–hole pairs was suppressed, and the light absorption range was expanded after constructing a heterojunction and doping with Ag, according to ultraviolet–visible (UV–vis) diffuse reflectance spectra and photoluminescence spectroscopy. Moreover, in the detection range of toluene gas (3 ppm–50 ppm), the response value of TiO(2)−CoFe(2)O(4)−Ag increased from 2 to 15, which was much higher than that of TiO(2)−Ag (1.7) and CoFe(2)O(4)−Ag (1.7). In addition, the working temperature was reduced from 360 °C to 263 °C. Furthermore, its response/recovery time was 40 s/51 s, its limit of detection was as low as 10 ppb, and its response value to toluene gas was 3–7 times greater than that of other interfering gases under the same test conditions. In addition, the response value to 5 ppm toluene was increased from 3 to 5.5 with the UV wavelength of 395 nm–405 nm. (4) Conclusions: This is primarily due to charge flow caused by heterojunction construction, as well as metal sensitization and chemical sensitization of novel metal doping. This work is a good starting point for improving gas-sensing capabilities for the detection of toluene gas.