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Scientists make ‘impossible material’ … by accident

Researchers in Uppsala, Sweden accidentally left a reaction running over the weekend and ended up resolving a century-old chemistry problem. Their work has led to the development of a new material, dubbed…

Not so sexy, but very useful. Simon Ydhag, Uppsala University

Researchers in Uppsala, Sweden accidentally left a reaction running over the weekend and ended up resolving a century-old chemistry problem. Their work has led to the development of a new material, dubbed Upsalite, with remarkable water-binding properties. Upsalite promises to find applications in everything from humidity control at home to chemical manufacturing in industry.

Maria Strømme and colleagues at Uppsala University, whose work appears in the journal PLOS ONE, have modified a procedure dating back to 1908 to make a powdered and dry form of magnesium carbonate (MgCO3). The reaction ingredients are all cheaply available: magnesium oxide (MgO) and carbon dioxide (CO2), dissolved in methanol, a common industrial solvent. The result is pure, dry MgCO3.

Dry in this case means very dry. In the chemical sense, it means void of almost any water molecules at all.

Crystalline forms of dry MgCO3, which lack the structure needed to absorb water, are readily synthesised at high temperatures (over 100 °C). As early as 1820, people started to search for lower-temperature routes to make dry MgCO3, but none have successfully yielded pure product until now. This is why Upsalite has been described as an “impossible material”.

The key modification was to increase the pressure of CO2 to three times that of normal atmospheric pressure, rather than simply bubbling the gas through a mixture of MgO in methanol. When one mixture was accidentally allowed to react over a long weekend, researchers came back to find a gel. It turns out the gel was formed because methanol molecules had been trapped within the material. When heated to 70 °C, which is above the boiling point of methanol, the gel “solidifies and collapses into a white and coarse powder”. Analysis confirmed that the product was just what chemists had been trying to make for more than 100 years – a dry, powdered form of MgCO3.

Upsalite has impressive properties as a desiccant, absorbing water better than the much more expensive materials that are currently used (called zeolites). Most of the absorbed water is retained when Upsalite is transferred from a humid to a very dry environment. The dry form can be regenerated by heating to 95 °C. By contrast, most zeolites need to be heated to over 150 °C in order to dry them. Not only is Upsalite easy to make and reuse, but it is also not toxic to humans, which makes it suitable for humidity control indoors.

The impressive drying property stems from the very large internal surface area of Upsalite. MgCO3 is a common mineral that occurs in a variety of forms, most of which have water bound to their surface and are crystalline. By contrast, Upsalite has no water integrated into its structure and is not crystalline. Instead, it is mesoporous – a structure with pores that are a million times smaller than the width of a human hair – which provide it with a much greater surface area.

The past 20 years have seen a surge of interest in mesoporous materials such as zeolites and carbon nanotubes due to their ability to selectively absorb small molecules, which may enable applications in drug delivery, pollution removal, and the development of new catalysts for chemical reactions. Recognizing these prospects, the researchers have founded a spin-out company called Disruptive Materials to commercialise and apply Upsalite.

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6 Comments sorted by

  1. Christopher Cheatle

    Retired

    This is entertaining and informative, thank. Does it have applications in agriculture and horticulture? Can the crystals both store and release water?

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    1. Andrew Bissette

      PhD student at University of Oxford

      In reply to Christopher Cheatle

      I couldn't find any examples of it actually being used yet, but given the novelty that's hardly surprising. A look round the web at comments on other articles such as this turns up plenty of ideas and speculation though.

      It does both store and release water: it will absorb water at even fairly low humidities. The release of water is achieved by heating to 95 C; I don't think this would be a useful application beyond being a very simple way to regenerate the anhydrous form. (i.e. I don't think it has an application in controlled release of water into a dry environment)

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  2. Paul Guy

    Scientist

    Serendipity has been a significant factor in many important discoveries. This looks like an important advance in technology.

    I am a little concerned about the line " it is also not toxic to humans". With the new an remarkable properties this compound has, can we be sure at this stage about its perceived innocuous nature?
    Asbestos is essentially non toxic, at least acutely.

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    1. Andrew Bissette

      PhD student at University of Oxford

      In reply to Paul Guy

      Anhydrous magnesium carbonate's toxicity profile is already very well understood and it is considered safe. See ref. 5 in the paper, which refers to the FDA's inactive ingrediemnts database.

      I wouldn't recommend inhaling the stuff but it seems like it will be considerably safer than desiccants such as silica gel.

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  3. Jose Garcia

    El presidente

    That's often the way, science is essentially trial and error.

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