Metal–Organic Framework-Derived Au-Doped In2O3 Nanotubes for Monitoring CO at the ppb Level

Achieving selective detection of ppb-level CO is important for air quality testing at industrial sites to ensure personal safety. Noble metal doping enhances charge transfer, which in turn reduces the detection limit of metal oxide gas sensors. In this work, metal-organic framework-derived Au-doped In₂O₃ nanotubes with high electrical conductivity are synthesized by pyrolysis of the Au-doped metal-organic framework (In-MIL-68) as a template. Gas-sensing experiments reveal that the detection limit of 0.2% Au-doped In₂O₃ nanotubes (0.2% Au, mass fraction) is as low as 750 ppb. Meanwhile, the sensing material shows a response value of 18.2 to 50 ppm of CO at 240 °C, which is about 2.8 times higher than that of pure In₂O₃. Meanwhile, the response and recovery times are short (37 s/86 s). The gas-sensing mechanism of CO is uncovered by in situ DRIFTS through the reaction intermediates. In addition, first-principles calculations suggest that Au doping of In₂O₃ significantly enhances its adsorption energy for CO and improves the electron transfer properties. This study reveals a novel synthesis pathway for Au-doped In₂O₃ nanotubular structures and their potential application in low concentration CO detection.