Light-Excited Ag-Doped TiO2−CoFe2O4 Heterojunction Applied to Toluene Gas Detection

Abstract

(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, TiO2−CoFe2O4−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 TiO2−CoFe2O4−Ag increased from 2 to 15, which was much higher than that of TiO2−Ag (1.7) and CoFe2O4−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.

Investigation of High-Sensitivity NO2 Gas Sensors with Ga2O3 Nanorod Sensing Membrane Grown by Hydrothermal Synthesis Method

“…Among several structures of gas sensors, a metal oxide semiconductor (MOS) gas sensor is the most attractive structure due to its inherent advantages of easy fabrication, simple operation, low prices, and a small size [ 3 ]. Many metal oxide semiconductor materials have played promising roles in resistive types of MOS-structured gas sensors, such as zinc oxide (ZnO) [ 4 , 5 ], stannic oxide (SnO 2 ) [ 6 , 7 ], titanium dioxide (TiO 2 ) [ 8 , 9 ], indium oxide (In 2 O 3 ) [ 10 , 11 ], and gallium oxide (Ga 2 O 3 ) [ 12 , 13 ]. Among the metal oxide semiconductor materials, in view of the advantages of non-toxicity, low prices, and good chemical stability [ 14 , 15 ], Ga 2 O 3 has potential applications in high-temperature gas sensors [ 16 , 17 ].…”