UiO-66 is an archetypal metal−organic framework (MOF) with a very high surface area as well as high thermal stability. It is found that the stability can be attributed to the metal oxide node being cuboctahedral allowing for 12 extension points for 1,4-benzenedicarboxylic acid (BDC) coordination. Because of this and its exceptional tunability and functionality, which are largely due to defect control of both missing-cluster and missinglinker defects, UiO-66 has gained scientific popularity. The combination of these characteristics allows for a highly versatile material that can be adapted to many different applications. The purpose for this work is to provide a historic overview of UiO-66, outlining the major developments that changed the synthesis strategies of Zr-based MOF as well as current and future works, which include defect control, aqueous crystallization, functionality-stability trade-offs, and advanced topographies. A breakdown of the various UiO-66 structures, including isoreticular and reo-type, and different characterization techniques such as powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and nitrogen porosimetry are discussed as well.

Advancing our understanding of the defect formation mechanism in metal–organic frameworks (MOFs) is critical for the rational design of the material’s structure. In particular, the defects in the UiO-66 framework have been shown to have a significant impact on the framework functionality and stability. However, the effects of synthesis conditions on defect formation are elusive and our understanding of missing-ligand and missing-cluster defects in UiO-66 is far from clear. In this work, we demonstrate that the formation of missing-cluster (MC) defects is due to the large number of partially deprotonated ligands in synthesis solution. The proposed mechanism is verified by a series of syntheses controlling the defect formation. The results show that the quantity of MC defects is sensitive to deprotonation reagents, synthesis temperature, and reactant concentration. The pore size distribution derived from the N2 adsorption isotherm at 77 K allows accurate and convenient characterization of the defects in UiO-66. The existence of defects in the UiO-66 framework can cause significant deviations in its pore size distribution from the results derived from the theoretically perfect crystal structure. The extra cavities generated by MC defects are demonstrated to allow deposition of a large functional molecule, ferrocene (3.5 Å × 4.5 Å × 4.5 Å). The successful incorporation is proven by the tuning of the original N2-selective framework to become an O2-selective framework.

The preparation and physical properties of a series of nanocomposites based on dispersions of Montmorillonite clays in thermoset epoxy resins are reported. The effects of the variation of the concentration of the clay and the influence of a change of the functionality of the epoxy compounds and the amine curing agent are reported. The effects of the method of dispersion of the clay are studied, and it was found that ultrasound provides an effective aid to dispersion of the clay platelets. In general, the addition of clay platelets leads to an increase in the glass-rubber transition, but in the case of a highly cross-linked system, the reverse effect was observed. The effects observed are discussed in the context of the way in which the chemical structure of the monomers influence the dispersion process and the structure of the final resin system.

MOFs can separate O 2 /N 2 mixtures via various mechanisms, making them a great candidate for many air separation applications. We show that the adsorptive behavior of MOFs can be classified based on whether they contain open metal sites (OMSs) and if those sites form a coordination bond with oxygen molecules. Existing data suggests that OMS MOFs that can bind O 2 have high O 2 /N 2 selectivity, while OMS MOFs that cannot form such a bond have increased selectivity toward N 2 . Monte Carlo simulations show that saturated metal site (SMS) MOFs selectively adsorb O 2 based on dispersion forces. Inaccuracies in simulations on nonbinding OMS MOFs are suggested as evidence that there are other nonbinding interactions impacting O 2 /N 2 adsorption in OMS MOFs. Monte Carlo simulations on SMS MOFs are used to define a volume-weighted average pore diameter to establish clear correlations between complex pore size distributions and adsorptive properties.

Hybrid steel-composite gears, which combine steel teeth with a fiber-reinforced polymer composite core, are a rapidly emerging technology for weight reduction in aerospace drivetrain systems. However, power transmission gears—and especially the requirement of rotorcraft gearboxes to operate under loss of lubrication—are a very challenging application for composite materials, due to the combination of mechanical and thermal loads. In this work, composite materials, including newly developed hybrid laminates featuring multiple grades of carbon fiber, are fabricated. Mechanical and thermal testing, along with ply-level finite element analysis, are employed to assess the suitability of these composite materials for hybrid aerospace gear applications. Particular focus is given to high-temperature epoxy and bismaleimide resins and to hybrid laminates reinforced by multiple grades of carbon fiber. This hybrid drivetrain technology would manifest significant weight reductions without compromising gear performance.