La-CoOx/N/C Nanocomposites Derived from Carbon Black-Loaded ZIF-67 for Low-Temperature Detection of Methane

Conventional metal oxide semiconductor (MOS) gas sensors have an inherent disadvantage of high operating temperatures and low sensitivity to weakly polarized gases, such as methane. This study mainly focuses on developing specialized MOS-based gas sensors for the highly sensitive detection of methane. Therefore, we designed and prepared Co3O4-based nanocomposites of La-CoOx/N/C via the pyrolysis of a La-doped zeolitic imidazolate framework (ZIF-67) hydrothermally grown on carbon black (CB) nanospheres. The resulting La-CoOx/N/C material is dominated by hollow nanospheres, owing to CB pyrolysis. In the as-formed nanocomposite, the dispersed La2O3 acts as a "fence" to prevent the agglomeration of Co3O4 nanoparticles and form rich heterojunctions. Meanwhile, N-coordinated carbon (N/C) acts as an anchor for La-CoOx attachment, which further improves the dispersion of the composite oxides and enhances their adsorption capacity for methane molecules. Consequently, the La-CoOx/N/C sensor demonstrated a response of 1.25 with 4/5 s recovery/response times for 600 ppm of methane at a relatively low temperature (130 °C). Furthermore, a methane-sensing mechanism is demonstrated based on heterostructure effects and first-principles calculations. The proposed La-CoOx/N/C gas sensor is a device that exhibits excellent methane sensing performance at low temperatures without requiring precious metals.