Specific Sn-O-Fe Active Sites from Atomically Sn-Doping Porous Fe₂O₃ for Ultrasensitive NO₂ Detection

Conventional gas sensing materials (e.g., metal oxides) suffer from deficient sensitivity and serve cross-sensitivity issues due to the lack of efficient adsorption sites. Herein, the heteroatom atomically doping strategy is demonstrated to significantly enhance the sensing performance of metal oxides-based gas sensing materials. Specifically, the Sn atoms were incorporated into porous Fe₂O₃ in the form of atomically dispersed sites. As revealed by X-ray absorption spectroscopy and atomic-resolution scanning transmission electron microscopy, these Sn atoms successfully occupy the Fe sites in the Fe₂O₃ lattice, forming the unique Sn-O-Fe sites. Compared to Fe-O-Fe sites (from bare Fe₂O₃) and Sn-O-Sn sites (from SnO₂/Fe₂O₃ with high Sn loading), the Sn-O-Fe sites on porous Fe₂O₃ exhibit a superior sensitivity (R_g/R_a = 2646.6) to 1 ppm NO₂, along with dramatically increased selectivity and ultra-low limits of detection (10 ppb). Further theoretical calculations suggest that the strong adsorption of NO₂ on Sn-O-Fe sites (N atom on Sn site, O atom on Fe site) contributes a more efficient gas response, compared to NO₂ on Fe-O-Fe sites and other gases on Sn-O-Fe sites. Moreover, the incorporated Sn atoms reduce the bandgap of Fe₂O₃, not only facilitating the electron release but also increasing the NO₂ adsorption at a low working temperature (150 °C). This work introduces an effective strategy to construct effective adsorption sites that show a unique response to specific gas molecules, potentially promoting the rational design of atomically modified gas sensing materials with high sensitivity and high selectivity.