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

• Heteroatom atomically doping strategy constructs highly efficient Sn–O–Fe sites on porous Fe2O3 for ultrasensitive NO2 detection. • Atomically dispersed Sn atoms occupy Fe sites in Fe2O3 lattice, creating unique Sn–O–Fe active sites with abundant oxygen vacancies. • Optimized Sn-Fe2O3 sensor exhibits ultra-high sensitivity (Rg/Ra = 2646.6 to 1 ppm NO2), ultra-low detection limit (10 ppb), and high selectivity. • Theoretical calculations reveal strong NO2 adsorption on Sn–O–Fe sites and reduced bandgap, enabling low-temperature operation at 150 °C.