ZIF-8 provides accessible channel to small molecules like hydrogen to pass through the pores to interact at the CuO:Al surface. The interaction strength of VOCs with ZIF-8 is defined by the electronic polarizability of tested VOCs.

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.

Advancements in material design, specifically the development of hybrids combining metal oxides (MO _x ) and zeolitic imidazolate frameworks (MOF/ZIFs), have revolutionized modern materials science by employing their synergistic effects and creating the hybrid interface MOF/MO _x . This work systematically examines the structural evolution, defect engineering, and thermal stability of zeolitic imidazolate framework (ZIF-7, ZIF-8, ZIF-67, and ZIF-71)-coated ZnO and Cd-doped ZnO columnar structures. Comprehensive characterization was performed on all four studied ZIFs, including scanning electron microscopy revealing dodecahedral morphology of ZIF particles, and in situ temperature-dependent X-ray diffraction showing smaller coherently scattering regions compared to the sizes of the particles. SEM images indicate that these particles are polycrystalline and show a large contribution of surface-related domains. Thermolysis behavior and bond energy analysis reveal the role of Co–N bonds in thermal degradation of ZIF-67 at 250 °C compared to Zn–N bond of ZIF-8, which degrades at 325 °C, although Co–N has a higher bond energy compared to Zn–N, attributed to unsaturated coordination of Co with N, which leads to easy oxygenation of a Co–N bond. In ZIF-71 and ZIF-8, peak shifts are observed at higher angles by increasing the temperature, which would point to a negative thermal expansion. Using current–voltage characteristics, an inverted hysteresis was observed by employing forward and reverse voltage sweep, which may be characterized as capacitive hysteresis attributed to charge traps that slow down the return path. Gas-sensing studies revealed functional implications that ZIF-67-coated ZnO exhibited selective VOC sensing at 250 °C and enhanced hydrogen sensing at 300 °C, with structure–property correlations elucidated through defect analysis. Other hybrid materials, such as ZIF-7-coated ZnO, ZIF-8-coated ZnO, and ZIF-71-coated ZnO, elucidate better hydrogen, n-butanol, and 2-propanol sensing compared to ethanol and acetone. Our findings highlight the critical role of ZIF type and Cd doping in tuning the structural, thermal, and functional properties of ZnO-based composites, offering new perspectives for the rational design of advanced sensing materials based on the hybrid interface MOF/MO _x .

Functional ceramics play a key role in technology, particularly in piezoelectric sensors and actuators, ferroelectric power generation, and durable semiconductors used in sensors and memristors. In this study, we report a versatile wet chemical synthesis approach, converting the surface of functional tetrapodal zinc oxide (t-ZnO) to common metal hydroxides. We performed structural, morphological, and interface characterization and explored the subsequent application of various t-ZnO@metal hydroxide/oxide core–shell structures. The t-ZnO core was initially uniformly coated with different metal hydroxides, forming distinct platelets in a core–shell architecture. Interface studies were conducted to investigate the chemical, structural, and morphological properties of these hybrid microstructures using 2D scanning nano X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), bulk XRD, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Our findings highlight the potential of exceptional t-ZnO structures as versatile templates, offering their morphology for the synthesis of derived oxides and hydroxides of many other elements while leveraging their structural advantages.

This study describes a procedure for preparing microfluidic chips made from polydimethylsiloxane (PDMS) layers. It uses an Ossila UV ozone cleaner for surface activation instead of the more common oxygen plasma treatment. The process is limited to PDMS@PDMS bonding, and it can be used when a low-cost procedure for a small number of microfluidic chips is required or when an oxygen plasma etcher is unavailable. The challenges of this process arise from the slight hardening of the PDMS surface when it is activated for at least 70 min, which is necessary for reliable bonding. Activation of the surface is confirmed by contact angle measurements. In a static simulation and lab tests, it is demonstrated that damage resulting from this hardening in conjunction with careless handling of the microfluidic chip is mitigated by incorporating predetermined break structures and using tubes with an outer diameter that is smaller than the inlets. Additionally, pre-polymerized PDMS glue and PDMS seals are suggested to ensure that the tubes are properly sealed. A burst test in air was performed to demonstrate the stability of the bonding and gluing. IR and XPS measurements were performed to investigate surface and bulk changes due to the treatment. To demonstrate the concept, six microfluidic chips were prepared and tested, achieving flow rates of at least 170 µL/min at ±180 mbar. Bonding remains stable up to a pressure of approximately 428 ± 60 mbar.