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 (Cu2O)] have been widely researched as good gas sensing materials due to their unique oxygen adsorption properties. In this work, C-doped CuO/Cu2O hollow nano-octahedrons have been prepared by thermal decomposition of the Cu-based metal–organic framework ([Cu3(BTC)2]n). The CuO and Cu2O 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 (O2–) content. Meanwhile, doping C in the lattice of the heterojunction effectively reduces the band gap of CuO/Cu2O and promotes the chemical reaction of the target gas on the surface of the material. Density functional theory calculations indicate that the CuO/Cu2O heterojunction has strong adsorption ability for NO2. Electrochemical impedance spectroscopy further reveals that C-doped CuO/Cu2O 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 (NO2) at room temperature (28 °C). In addition, the sensor has extremely low detection, which can detect parts per billion level NO2 (20.50% to 100 ppb). It is expected to provide a reference for the development of a room-temperature NO2 sensor.