Metal-Organic Frameworks (MOFs) As Hydrogen Storage Materials At Near-Ambient Temperature.

Hydrogen may play a critical role in our efforts to de-carbonize by 2050. However, there remain technical challenges in the storage and transport of hydrogen. Metal-organic frameworks (MOFs) have shown significant promise for hydrogen storage at cryogenic temperatures. A material that can meet the US department of energy (DOE) ultimate goal of 6.5 wt. % for gravimetric performance and 50 g/L for volumetric storage at near-ambient temperatures would unlock hydrogen as a future fuel source for on-board applications. Metal-organic frameworks typically have low heat of adsorptions (i. e. 4-7 kJ/mol), whereas for storing significant quantities of hydrogen at near-ambient temperatures, 15-25 kJ/mol is likely required. In this review we explore the current methods used (i. e., open-metal sites, alkali dopants and hydrogen spillover) for promoting strong adsorption within MOFs. Further we discuss MOF-based materials with respect to the technical aspects of deliverable capacity, kinetics and stability.

Tailoring the chain packing in ultrathin polyelectrolyte films formed by sequential adsorption: nanoscale probing by positron annihilation spectroscopy.

Depth profiling experiments by positron annihilation spectroscopy have been used to investigate the free volume element size and concentration in films assembled using the layer-by-layer (LbL) adsorption method. Films prepared from strong polyelectrolytes, weak polyelectrolytes, hydrogen-bonding polymers, and blended polyelectrolyte multilayers have different chain packing that is reflected in the free volume characteristics. The influence of various parameters on free volume, such as number of bilayers, salt concentration, solution pH, and molecular weight, has been systematically studied. The free volume cavity diameters vary from 4 to 6 Å, and the free volume concentrations vary from (1.1-4.3) × 10(20) cm(-3), depending on the choice of assembly polymers and conditions. Films assembled from strong polyelectrolytes have fewer free volume cavities with a larger average size than films prepared from weak polyelectrolytes. Blending the weak polyanion poly(acrylic acid), PAA, with the strong polyanion poly(styrene sulfonate), PSS, to layer alternately with the polycation poly(allyamine hydrochloride), PAH, is shown to be a viable method to achieve intermediate free volume characteristics in these LbL films. An increase in salt concentration of the adsorption solutions for films prepared from strong polyelectrolytes makes these films tend toward weaker polyelectrolyte free volume characteristics. Hydrogen-bonded layered films show larger free volume element size and concentration than do their electrostatically bonded counterparts, while reducing the molecular weight of these hydrogen-bonded polymers results in slightly reduced free volume size and concentration. A study of the effect of solution pH on films prepared from weak polyelectrolytes shows that when both polyelectrolytes are substantially charged in solution (assembly pH = 7.5), the chains pack similarly to strong polyelectrolytes (i.e., lower free volume concentration), but with smaller average cavity sizes. These results give, for the first time, a clear indication of how the free volume profile develops in LbL thin films, offering numerous methods to tailor the Ångström-scale free volume properties by judicious selection of the assembly polymers and conditions. These findings can be potentially exploited to tailor the properties of thin polymer films for applications spanning membranes, sensing, and drug delivery.

Leaching Behavior and Corrosion Inhibition of a Rare Earth Carboxylate Incorporated Epoxy Coating System.

While paint coatings act as important barriers to corrosion, defects can lead to localized, rapid metal loss. The addition of corrosion inhibitors that are capable of leaching from a coating to protect the metal surface at a defect can prevent this type of corrosion. This work investigates the release and corrosion protection capabilities of two rare earth (RE) carboxylate inhibitors from an epoxy coating as an initial step to understanding their leaching behavior and interaction with the coating system. Leaching experiments were performed via inductively coupled plasma mass spectroscopy (ICP-MS) analyses of the solutions in which free-standing coatings loaded with varying concentrations of inhibitor compounds had been immersed. Inhibitor release from the epoxy coating was observed to be dependent on initial inhibitor concentration, inhibitor chemistry, and solution pH conditions. The coating systems with greater initial inhibitor loadings showed higher leaching rates, particularly in acidic environments. Following immersion, the absence of characteristic inhibitor peaks in the FTIR spectra of the coatings also confirmed leaching had taken place. Cross-sectional views of the coatings after exposure to the pH 1 environment presented a chloride infusion zone at the coating/solution interface where the inhibitor had leached out. The RE active inhibition provided by the leached RE carboxylate inhibitors was verified by exposure of a coating defect to a chloride contaminated environment.

Versatile, high quality and scalable continuous flow production of metal-organic frameworks.

Further deployment of Metal-Organic Frameworks in applied settings requires their ready preparation at scale. Expansion of typical batch processes can lead to unsuccessful or low quality synthesis for some systems. Here we report how continuous flow chemistry can be adapted as a versatile route to a range of MOFs, by emulating conditions of lab-scale batch synthesis. This delivers ready synthesis of three different MOFs, with surface areas that closely match theoretical maxima, with production rates of 60 g/h at extremely high space-time yields.

Combining UV lithography and an imprinting technique for patterning metal-organic frameworks.

Thin metal-organic framework (MOF) films are patterned using UV lithography and an imprinting technique. A UV lithographed SU-8 film is imprinted onto a film of MOF powder forming a 2D MOF patterned film. This straightforward method can be applied to most MOF materials, is versatile, cheap, and potentially useful for commercial applications such as lab-on-a-chip type devices.

A new method to position and functionalize metal-organic framework crystals.

With controlled nanometre-sized pores and surface areas of thousands of square metres per gram, metal-organic frameworks (MOFs) may have an integral role in future catalysis, filtration and sensing applications. In general, for MOF-based device fabrication, well-organized or patterned MOF growth is required, and thus conventional synthetic routes are not suitable. Moreover, to expand their applicability, the introduction of additional functionality into MOFs is desirable. Here, we explore the use of nanostructured poly-hydrate zinc phosphate (α-hopeite) microparticles as nucleation seeds for MOFs that simultaneously address all these issues. Affording spatial control of nucleation and significantly accelerating MOF growth, these α-hopeite microparticles are found to act as nucleation agents both in solution and on solid surfaces. In addition, the introduction of functional nanoparticles (metallic, semiconducting, polymeric) into these nucleating seeds translates directly to the fabrication of functional MOFs suitable for molecular size-selective applications.