MOF-Derived Binary Nanophases of Metal Oxides and Oxidized Carbon for Highly Selective and Long-Lived Gas Sensing

Highly selective and durable chemiresistive gas sensing demands architectures that enable rapid analyte transport, strong interfacial reactivity, and stable charge transduction over prolonged operation. Here, we report a sensing layer derived from a Sn-based metal-organic framework (Sn-MOF), in which oxidative conversion transforms the Sn-MOF into a nanometer-scale binary nanophase of rutile SnO2 and oxidized carbon within an open, web-like, junction-rich mesoporous network. In this architecture, ultrafine SnO2 nanodomains are intimately integrated with a retained oxidized carbon binary nanophase, co-engineering gas accessibility, surface redox activity, and electrical transport continuity in a single layer. The resulting binary nanophase enables highly selective and quantitative formaldehyde (HCHO) detection, achieving a limit of detection as low as 0.43 ppb and an electrical response on the order of 2.8 × 104 at 10 ppm HCHO, with rapid response/recovery times of 5.4/27.4 s at 350 °C. The sensing characteristics surpass the performance of reported nanomaterials such as SnO2 nanoparticle and MOF-derived HCHO sensors. Notably, the sensor is stable over 14 weeks of continuous operation and preserved its rutile SnO2/oxidized-carbon nanophase, even in humid conditions.