Detection of Ppb-level NO2 using mesoporous ZnSe/SnO2 core-shell microspheres based chemical sensors

Detection of ultralow concentrations of the hazardous gases is the major demand and challenge for the development of biosensors. A novel mesoporous ZnSe-core/SnO2-shell microspheres based chemiresistive-type sensor was fabricated for ppb-level NO2 detection, and the theoretical detection limit is calculated to be 0.87 ppb. The as-fabricated sensor presents an excellent performance for low-concentrations of NO2 up to 2.4 ppm and exhibits significantly higher response approximately 6.94 than those of pristine SnO2 (similar to 2.86) and ZnSe based sensors (almost no response) to 2.4 ppm NO2 at 160 degrees C. The response and recovery time of the core-shell microspheres based sensor are 64 s and 52 s, respectively, which are substantially improved compared to those of the pristine SnO2 based sensor (similar to 149 s and similar to 133 s). The sensor demonstrates a superior long-term stability with a deviation in the response of the sensor less than 5 % for one month, and a brilliant selectivity to several possible interferents. The significantly improved sensing performance could be attributed to the obtained mesoporous structures and the formed ZnSe/SnO2 hybrid interfaces. It yields more active sites and promotes the electrons transferred between ZnSe and SnO2 nanocrystals. The density functional theory (DFT) calculations are employed to reveal the potential transducing mechanisms.