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New Nanoscopic Pore Gas Storage for Next-Generation Clean Energy Vehicles

Tremendous amounts of hydrogen and methane can be stored in nanoscopic pores.

A research team led by Northwestern University has designed and synthesized new materials with ultrahigh porosity and surface area for the storage of hydrogen and methane for fuel cell-powered vehicles. These gases are attractive clean energy alternatives to carbon dioxide-producing fossil fuels.

The designer materials, a type of a metal-organic framework (MOF), can store significantly more hydrogen and methane than conventional adsorbent materials at much safer pressures and at much lower costs.

“We’ve developed a better onboard storage method for hydrogen and methane gas for next-generation clean energy vehicles,” said Omar K. Farha, who led the research. “To do this, we used chemical principles to design porous materials with precise atomic arrangement, thereby achieving ultrahigh porosity.

The universal truth about sticky surfaces

Trapping molecules on custom-designed porous surfaces becomes easier with a new model that unifies previous theories of adsorption.

Many purification tools, from simple charcoal filters to complex desalination plants, rely on solids with millions of tiny pores to capture and remove contaminants without chemically binding to them. Now, a KAUST team has identified the key factors that connect adsorption on different kinds of porous surfaces, solving century-old problems of predicting uptake on unknown substances.

In the early 1900s, the concept of adsorption isotherms emerged to describe how adsorbents behave in the presence of steadily increasing amounts of molecules. These graphs have distinct shapes that depend on atom-scale surface properties-for example, whether particles stick in single layers or multilayers-and quickly became essential for designing and understanding purification setups. The majority of absorbents, chemists found, could be sorted into one of six isotherms after a few experimental measurements.

However, modern absorbents with heterogeneous pore structures, such as metal-organic frameworks (MOFs), are proving more difficult to model. While these materials benefit from high-throughput testing of numerous samples, the need for individual isotherm measurements slows discovery considerably-a situation experienced by Professor Kim Choon Ng at KAUST's Water Desalination and Reuse Center.

MOF keeps humidity in the Goldilocks zone

A novel porous material can soak up excessive humidity in a room only to release it again when the humidity falls. Now KAUST researchers have devised a metal-organic framework (MOF) material that monitors its own properties.

MOFs are a class of microporous materials consisting of single metals or metal clusters connected by organic linker molecules. By varying metals and organic linkers, researchers can precisely control the shape, size and functionality of the material's micropore system, which in turn affects the material's capacity for adsorbing certain molecules. Various MOFs have been designed to selectively capture carbon dioxide, for example. Others have been designed to adsorb water vapor.

This new MOF can regulate conditions perfectly within the window of comfortable and healthy humidity levels established by the American Society of Heating, Refrigeration and Air Conditioning Engineers. It could be used to modulate humidity in indoor spaces, aircraft cabins or even space shuttles.

Adsorbent that can selectively remove water contaminants

Professor Cafer T. Yavuz and his team at the Graduate School of Energy, Environment, Water, and Sustainability (EEWS) of Korea Advanced Institute of Science and Technology (KAIST) have developed an adsorbent that can selectively capture soluble organic contaminants in water.

This water treatment adsorbent is a fluorine-based nanoporous polymer that can selectively remove water-soluble micromolecules. It has the added advantage of being cheap and easily synthesized, while also being renewable.

The results of this research have been published online in Nature Communications on November 10, 2016. The research paper is titled "Charge-specific Size-dependent Separation of Water-soluble Organic Molecules by Fluorinated Nanoporous Networks."

Water pollution is accelerating as a result of global industrial development and warming. As new materials are produced and applied in the agricultural and industrial sectors, the types of contaminants expelled as sewage and waste water are also becoming diverse.

Super-adsorbent MOF captures twice its weight in water

Material chemists in the Kingdom of Saudi Arabia have developed a superporous solid made up of a patchwork of metal ions and organic linkers (a metal-organic framework, or MOF) that can suck up to 200% of its own weight in atmospheric moisture. The technology, presented January 11 in the journal Chem, could be applied to regulating humidity levels, particularly in confined environments such as aircraft cabins and air-conditioned buildings.

"I am not surprised that MOFs surpass existing solids in their water capacity uptake," says senior author Mohamed Eddaoudi, of the King Abdullah University of Science and Technology. "MOFs' modularity, ultra-high surface areas, and large pore volumes, combined with the ability to control the pore surface functionality and pore size and shape, place MOFs as prospective candidates for energy-efficient and cost-effective humidity-control systems."

Permanently porous superabsorbent materials, with the combined requisite hydrolytic stability and significant water uptake, are challenging to make because most porous solids are either too dense or too reactive to water. Eddaoudi and his collaborators overcame this problem with their design of Cr-soc-MOF-1, a MOF made up of chromium ions linked together by carboxylate-based organic ligands that leave well-defined cages and channels for water to collect. The chromium ions are held in place by carboxylate moieties in a bidentate fashion, forming a rigid hexacarboxylate oxo-trinuclear chromium(III) cluster, ensureing that the resultant Cr-soc-MOF-1 adsorbent possess the required hydrolytic stability.