Ultrasensitive Sensors Based on PdO@SrFe₂O₄ Nanosphere-Modified Fibers for Real-Time Monitoring of Ethanol Gas

Spinel ferrites have attracted great interest in the research of sensing materials due to their excellent catalytic activity and flexible and tunable physical properties. Here, we report an environmentally friendly technique using an electrospinning system, followed by a hydrothermal method, to fabricate a highly sensitive ethanol sensor based on PdO nanosphere-modified SrFe2O4 fibers for real-time monitoring. From the evaluation of SEM, TEM, XRD, XPS, and BET, it is clear that the PdO nanospheres firmly adhere to the surfaces of SrFe2O4 fibers, which are composed of smaller grains and have a large surface area with a huge amount of adsorbed oxygen species. Comparison of the sensing performance of different amounts of loaded PdO nanospheres into SrFe2O4 fibers shows that the sensor C-2 based PdO@SrFe2O4 composite shows high selectivity for ethanol over other interfering gases with a high sensitivity of 16.4 at a relatively low temperature of 150 °C toward 20 ppm ethanol with fast response/recovery speed (13 s/20 s) and a low detection limit (100 ppb). Through long-term studies, it was found that the sensor was stable over a period of 60 days. Consequently, the superior sensing selectivity of C-2 based PdO@SrFe2O4 composite toward ethanol gas is attributed to the loading of PdO nanospheres into SrFe2O4 fibers, which could be effective due to charge transmission, spillover influence, and Fermi energy transferals as well as a huge surface area, and heterojunction impact can stimulate faster gas transmission kinetics and generate more catalytic spots on the surface of the sensing material. This research presents a general method for monitoring volatile organic pollutants with an ultrasensitive sensor based on spinel ferrites modified by noble metal oxide.