ZIF-71-Coated CuO:Al with Enhanced Gas-Sensing Performance for n‑Butanol and Hydrogen

In this study, hybrid materials combine metal-organic framework (MOF)-zeolitic imidazolate framework (ZIF) with inorganic metal-oxide semiconductors, resulting in composite materials that exhibit synergistic properties and improves the sensing capabilities of organic/inorganic hybrid sensors. MOFs provide tunable porosity and structural flexibility. Therefore, they present significant potential for gas-sensing applications. In this study, we report a simple and scalable approach to fabricate MOF ZIF-71-coated Al-doped CuO-based (CuO:Al) hybrid gas sensors. CuO:Al films with triangular-shaped grains were synthesized via a chemical solution approach. Comprehensive structural and surface analyses were conducted by using XRD, SEM, and XPS to elucidate crystallinity, morphology, and chemical states. The analysis revealed a highly crystalline structure with well-distributed ZIF-71 nanoparticles exhibiting a broad particle size range (500 to 750 nm) on the CuO:Al film. Raman spectroscopy and nitrogen (N₂) adsorption-desorption isotherms were employed to assess the vibrational properties and porosity. These techniques provided local bonding information on the linker arms and demonstrated the microporosity and pore size distribution of the ZIF-71 nanoparticles. Thermal stability was evaluated by thermogravimetric analysis, confirming the sensor's robustness under operational conditions. Gas-sensing studies reveal that the ZIF-71-coated CuO:Al sensors exhibit enhanced response (S = 11%) toward n-butanol at 200 °C and hydrogen gas (S = 61%) at an operating temperature of 250 °C. Due to n-butanol's strong affinity for ZIF-71 and its high interaction strength at 200 °C, the resulting adsorption capacity improves detection sensitivity at the ZIF-71/CuO:Al interface in the developed hybrid sensor. Good repeatability and durability of the fabricated gas sensors were observed for hydrogen gas in humid conditions. The gas-sensing performance was measured at 21-day intervals. During each measurement, the sample was exposed to elevated temperatures, effectively subjecting it to thermal treatment. As a result, improved sensing performance was observed after each measurement, which was attributed to the cumulative effects of thermal exposure. These findings highlight the potential of the MOF-ZIF-71-coated CuO:Al hybrid sensors for selective, humidity-tolerant, and stable detection of n-butanol and hydrogen gas. Further optimization is suggested to enhance the selectivity and lower the operational temperature.