High School Biology and Chemistry High School Engineering

Aladdin’s Genie in Mechanochemistry

If the genie from Aladdin were a molecule... He would be a metal-organic framework.

When scientists combine non-living materials with living counterparts, what do we get? Bionic people, superheroes, and artificial limbs that are often stronger than the original.

Well, what happens when we do the same at a molecular level? What about when metals –metal ions– are sewn to organic compounds or chains of ditopic or polytopic organic carboxylates?

The What

We get Aladdin’s genie, the one who makes passerby molecules fall in love and has the potential to eliminate villains by trapping them in his lamp. Not literally. But we do get metal-organic frameworks (MOFs): the shape-shifters and sirens of chemistry.

The function of each metal-organic framework is determined by two properties: their adhesive walls (dependent on which molecules attract each other), the size of their pores (which molecules can pass through the walls), and the geometry of their form (the spaces in between the atoms).

Their usefulness depends on the amount of energy it takes to extract the molecules it “absorbs,” the temperature they can be used at (the genie’s lamp “activates” with heat), and their chemical stability around different elements.

Out of more than 20,000 different MOFs reported in the past decade [1] with an infinite supply to come, we will take a look at MOF-801 and why MOFs provide an answer to world crises.

PacMan
Like PacMan, MOFs “eat up” the molecules they have an affinity for.

The How

MOFs are crystalline macromolecules comprised of metal ions or metal ion clusters (“nodes”) covalently bonded with “ligands” made from organic molecules [2]. They soak up other molecules by allowing them to pass through their pores and attach to the inner surfaces. Thus, the capacity of the MOF is often determined by its surface area under a certain vapor pressure aside from its chemical polarity.

MOF structure and function
a) The big yellow spheres represent the possible locations targeted molecules can attach to on the framework. b) The small yellow spheres represent the metal ion clusters connected by black lines representing ligands or linkers. Photo by Kim Hyunho.

MOFs are naturally found as minerals, but these minerals are often not as complex or strong. To make them, like witch’s brew, solvents are boiled off at high temperatures to leave behind powders that are then placed in other solvents with different boiling points for hours or days, repeating this exchange of solvents until the MOF reaches its desired properties [3]. Except, the process needs to be near perfect to ensure that the pores do not collapse or become clogged, so their making, which uses carbon dioxide in a hybrid liquid/gas phase, is carried out at high, specific temperatures and pressures [3].

The MOFs stable in the presence of water molecules are capable of attracting water molecules and trapping them. The process of extraction, similar to other methods for different MOFs and their victims, requires heat to release.

The device created by MIT and Berkeley does just that: it “consumes” the water molecules in humid air throughout the cool night and releases them onto a thermoelectrically cooled plate when the temperature warms up so that the water condenses on the plate. The water collects in minutes and the process repeats itself.

Water Harvester
The water harvesting device constructed by MIT Evelyn Wang’s student Kim Hyunho. Picture by V. ALTOUNIAN/SCIENCE.

The Where

Ideally, this device, the water-harvesting device can be implemented in regions across the globe where there is a large temperature gap throughout the day; water can be collected at night and released during the day. While there are MOFs which function at different levels of humidity, the MOF-801-P and MOF-841 are the most water stable, do not lose capacity after five adsorption/desorption cycles, are easily regenerated at room temperature, and encompass the lowest levels of humidity [4]. The MOF-801 can be functional in areas with a humidity as small as 10%, producing 0.28 kg of water collected per kg of the absorbent where the MOF-841 is functional in 20% humidity and on, producing 0.4 kg of water per kg of absorbent [4].

However, with the advancements made in this field, MOFs can be constructed to be relevant in all types of climates and conditions.

The Who

ION-X cylinder
The ION-X cylinders used to capture and transport hazardous gases by NuMat.

Nearly two decades ago, University of California, Berkeley Professor of Chemistry and Director for Molecular Foundry at Lawrence Berkeley National Laboratory [5] Omar Yaghi discovered the potential of this family of crystalline powders and developed the first of the porous crystals [6]

The chemical company BASF uses MOFs to power vehicles.

TruPick keeps fruits and vegetables fresh after harvest.

The Queens University Belfast company, MOF Technologies, uses MOF adsorbents for storage and release of the ethylene of ripening fruit and causes premature aging, producing 100 kg per week of a variety of these compounds.

The Northwestern University company, NuMat Technologies, delivers MOF-integrated products in which hazardous gases used in the electronics industries can be stored.

A number of scientist- and engineer-initiated companies are making these products available to the market and stimulating the MOF research. With the sustainability and commercial revenue, funding agencies and private investors continue to support MOF research.

The costs? An estimated $35 to $71 per kilogram using an engineering scale-up of laboratory-demonstrated synthesis procedures and conditions. Liquid assisted grinding (LAG) and aqueous synthesis are predicted to decrease the costs by 34-83%. [7] Its only a handful of years before we achieve a production of costs less than $10/kg and mass production.

 

The Why

MOF uses
The many uses of MOFs as depicted in this chart by the Royal Society of Chemistry.

The uses of MOFs apply to multiple disciplines and are a more efficient way of storing, transporting, and interacting with different substances because of their compactness, material properties, and availability. Gallons of gases can be stored in grams of the absorbent, eliminating endless accidents and challenges in many industries.

It’s the activated charcoal for nature, except rather than absorbing everything, it can be tailored to absorb specified targets.

Perhaps one day, edible MOFs will be used to eliminate diseases, bacteria, and tumors from our bodies by riding on smart pills that identify where our immune systems need reinforcement [8].

Greenhouse gases will be stored away in these sponges [9] and perhaps used to power our world [10].

Strawberries will no longer bear the oppression of fungus [11].

Batteries will be made of these easily manufactured compounds [12].

And the best part? It’s all thanks to science.

Aladdin and Genie
Aladdin analogy to MOFs.

You can be a scientist too!

Check out this link: http://mausdin.github.io/MOFsite/maker.html and make your own metal organic framework molecule!

References:

[1] Furukawa, Hiroyasu, et al. “The Chemistry and Applications of Metal-Organic
Frameworks.” Science, American Association for the Advancement of Science, 30 Aug. 2013, science.sciencemag.org/content/341/6149/1230444.

[2] ServiceApr, Robert F., et al. “This New Solar-Powered Device Can Pull Water Straight from the Desert Air.” Science | AAAS, American Association for the Advancement of Science, 8 Dec. 2017, http://www.sciencemag.org/news/2017/04/new-solar-powered-device-can-pull-water-straight-desert-air.

[3] Sherburne, Morgan. “A Better Way to Produce Metal-Organic Frameworks.” University of Michigan News, 18 Oct. 2017, news.umich.edu/a-better-way-to-produce-metal-organic-frameworks/.

[4] “MOF-841.” MOF-841 | Berkeley Global Science Institute, globalscience.berkeley.edu/mof-841.

[5] “MOFs: Metal–Organic Frameworks.” Chemistry World, 27 Apr. 2017, http://www.chemistryworld.com/podcasts/mofs-metalorganic-frameworks-/3007204.article.

[6] Chandler, David, and MIT News Office. “Water, Water Everywhere … Even in the Air.” MIT News, 14 Apr. 2017, news.mit.edu/2017/MOF-device-harvests-fresh-water-from-air-0414.

[7] D. Mircea, D. Anne, L. Yun, B. Craig, N. Dan, and L. Jeffrey. “Hydrogen Storage in a Microporous Metal−Organic Framework with Exposed Mn2+ Coordination Sites.” Journal of the American Chemical Society, 12 January 2006, https://doi.org/10.1021/ja0656853.

[8] Furukawa, H, et al. “Water Adsorption in Porous Metal-Organic Frameworks and Related Materials.” Advances in Pediatrics., U.S. National Library of Medicine, 19 Mar. 2014, http://www.ncbi.nlm.nih.gov/pubmed/24588307.

[9] “MOFs Find a Use.” Chemistry World, 28 Mar. 2017, http://www.chemistryworld.com/feature/mofs-find-a-use/2500508.article.

[10]  “Frameworks for Commercial Success.” Nature News, Nature Publishing Group,
21 Oct. 2016, http://www.nature.com/articles/nchem.2661.

[11] “Edible Gas Storage: Porous Metal-Organic Framework Made from Food-Grade Natural Products.” Phys.org – News and Articles on Science and Technology, Phys.org, phys.org/news/2010-09-edible-gas-storage-porous-metal-organic.html.

[12] “Water Adsorption in Porous Metal–Organic Frameworks and Related Materials.” C&EN: WHAT’S THAT STUFF? JELL-O, pubs.acs.org/doi/full/10.1021/ja500330a?src=recsys&mobileUi=0.

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