Oxygen vacancy engineering of self-doped SnO_{2-: X} nanocrystals for ultrasensitive NO₂ detection

It remains a great challenge to engineer oxygen vacancies in metal oxides and elucidate the interrelation between oxygen vacancy contents and gas sensing performance. Herein, we report the self-doping of SnO_2-x nanocrystals (NCs) through a solvothermal reaction using Sn powder and SnCl₄ as precursors. The effect of Sn²⁺ doping concentration in the SnO_2-x lattice on the nanocrystal size, band structure, and oxygen vancancies was investigated in detail. Gas-sensing tests revealed that the SnO_2-x NCs showed ultra-high sensitivity to NO₂ with low optimal operating temperature (100 °C). The detection limit of the sensor was as low as 500 ppb. This phenomenon is attributed to the active role of oxygen vancancies during the surface reactions with NO₂, which was substantiated by in situ reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). This work highlights the possibility of simultaneous engineering of surface energistics and electronic properties of SnO₂ based materials and provides an effective strategy to achieve excellent gas sensing performance for NO₂ gas sensors.