As the necessary transition to a supply of renewable energy moves forward rapidly, hydrogen (H₂) becomes increasingly important as a green chemical energy carrier. The manifold applications associated with the use of hydrogen in the energy sector require sensor materials that can efficiently detect H₂ in small quantities and in gas mixtures. As a possible candidate, we here present a metal-organic framework (MOF, namely ZIF-8) functionalized metal-oxide gas sensor (MOS, namely ZnO). The gas sensor is based on single-crystalline tetrapodal ZnO (t-ZnO) microparticles, which are coated with a thin layer of ZIF-8 ([Zn(C₄H₅N₂)₂]) by a ZnO conversion reaction to obtain t-ZnO@ZIF-8 (core@shell) composites. The vapor-phase synthesis enables ZIF-8 thickness control as shown by powder X-ray diffraction, thermogravimetric analysis, and N₂ sorption measurements. Gas-sensing measurements of a single microrod of t-ZnO@ZIF-8 composite demonstrate the synergistic benefits of both MOS sensors and MOFs, resulting in an outstanding high selectivity, sensitivity (S ≅ 546), and response times (1-2 s) to 100 ppm H₂ in the air at a low operation temperature of 100 °C. Under these conditions, no response to acetone, n-butanol, methane, ethanol, ammonia, 2-propanol, and carbon dioxide was observed. Thereby, the sensor is able to reliably detect H₂ in mixtures with air and even methane, with the latter being highly important for determining the H₂ dilution level in natural gas pipelines, which is of great importance to the energy sector.

Two different metal‐organic frameworks containing 2,5‐pyrazinedicarboxylate (PzDC²⁻) as linker molecule and hexanuclear {Hf₆(μ₃‐O)₄(μ₃‐OH)₄} clusters were obtained under solvothermal reaction conditions at 120 °C. Formic acid as the solvent leads to the formation of Hf‐UiO‐66‐PzDC ([Hf₆(μ₃‐O)₄(μ₃‐OH)₄(OH)₄(H₂O)₄(PzDC)₄]), while the reaction in a water/formic acid mixture resulted in the crystallisation of Hf‐CAU‐22‐PzDC ([Hf₆(μ₃‐O)₄(μ₃‐OH)₄(μ‐OH)₂(OH)₄(H₂O)₄(PzDC)₃]). The UiO‐66 compound is a new member of the large class of UiO‐66‐type MOFs. Hf‐CAU‐22 contains a chain of condensed {Hf₆O₄(OH)₄(μ‐OH)₄} clusters as the IBU, which is new to Hf‐MOF chemistry. For both MOFs, a detailed characterization, i. e. structure refinement from powder X‐ray diffraction data, ¹H‐NMR‐spectroscopy, elemental and thermogravimetric analyses and N₂ sorption measurements, was carried out. Hf‐UiO‐66‐PzDC undergoes a dehydration around 215 °C and framework decomposition starts at 315 °C. From N₂ sorption measurements, a maximum BET surface area of 460 m²/g was determined. The dehydration of Hf‐CAU‐22‐PzDC starts at 200 °C and the framework decomposition at 325 °C. The BET surface area was determined to 170 m²/g.

This study describes a procedure for preparing microfluidic chips made from polydimethylsiloxane (PDMS). It uses a UV ozone cleaner for surface activation instead of the more common oxygen plasma treatment. Although this process has some limitations compared to oxygen plasma bonding, 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 70 minutes, which is necessary for reliable bonding. 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. To demonstrate the concept, two microfluidic structures 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 0.5 bar.

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.