Cu-MOF-Derived C-Doped CuO/Cu₂O Hollow Nano-Octahedrons for Room-Temperature NO₂ Sensing at the ppb Level

P-type semiconductors [copper oxide (CuO) and cuprous oxide (Cu 2 O)] have been widely researched as good gas sensing materials due to their unique oxygen adsorption properties. In this work, C-doped CuO/Cu 2 O hollow nano-octahedrons have been prepared by thermal decomposition of the Cu-based metal–organic framework ([Cu 3 (BTC) 2 ] n ). The CuO and Cu 2 O nanoparticles form nano-octahedron heterojunctions by a close packing mode. A large number of active heterojunction sites were exposed, which significantly increased the adsorbed oxygen (O 2 – ) content. Meanwhile, doping C in the lattice of the heterojunction effectively reduces the band gap of CuO/Cu 2 O and promotes the chemical reaction of the target gas on the surface of the material. Density functional theory calculations indicate that the CuO/Cu 2 O heterojunction has strong adsorption ability for NO 2 . Electrochemical impedance spectroscopy further reveals that C-doped CuO/Cu 2 O hollow nano-octahedrons-40 min heterojunction has the best electron transport performance. The sensors have good gas sensing response (22.88–50 ppm) and selectivity to nitrogen dioxide (NO 2 ) at room temperature (28 °C). In addition, the sensor has extremely low detection, which can detect parts per billion level NO 2 (20.50% to 100 ppb). It is expected to provide a reference for the development of a room-temperature NO 2 sensor.