High sensitivity and high humidity resistance of p-p heterostructure CaFe2O4/Ca2Fe2O5 based sensor to ethanol under UV-visible light

Gas sensors with high sensitivity and high humidity resistance have broad application prospects in air monitoring and detection of exhaled biomarkers. Structural design and light-activated gas sensing technologies have been proposed as new strategies to improve the gas sensing performance of sensors. In this work, a series of Ca-Fe nanocomposite were prepared using a sol-gel method. The effects of annealing temperature on the phase structure and microstructure of the nanocomposites were systematically studied, and the sensing responses to ethanol vapour under different relative humidity (RH) and light conditions were compared. A novel CaFe2O4/Ca2Fe2O5 (CF2/CF) nanocomposite with a p-p heterostructure was obtained by annealing at 700°C. The microstructure of “nanorods + nanoparticles” indicated the formation of a composite phase structure. Notably, high ethanol sensing response of 3.95 was obtained for the CF2/CF-based sensor under 4 ppm ethanol at 69% RH and moderate operating temperature of 160°C, indicating high sensitivity and good humidity resistance. It was found that the ethanol sensing response of the CF2/CF-based sensor was significantly improved under light illumination. Compared to that in dark, the CF2/CF based sensor exhibited notably enhanced ethanol sensing responses of 20%, 13.5%, 8.5%, and 7.9% under 370 nm, 420 nm, and 470 nm light as well as natural light, respectively. The observed high sensitivity and high humidity resistance of the CF2/CF nanocomposites were attributed to the p-p heterojunction structure, light illumination and nature of both CF2 and CF materials. The p-p heterostructure CF2/CF nanocomposites contribute significantly to the development of gas sensors with high sensitivity.