The most common way to produce high surface area materials with micro-mesoporous structures — those with pore diameters below 50 nm — is to use soft templates and build a more rigid structure around them after which the template is eluted with a solvent or burnt away to produce the rigid porous material.
However, thanks to a mistake made by researchers at Uppsala University, Uppsala, Sweden, it's now possible — at low temperatures and without the use of templates — to synthesize a unique high-surface-area nanostructure with a well-defined pore-size distribution of ≤6-nm pores. Furthermore, the material — magnesium carbonate — is widely used, non-toxic, GRAS (generally-recognized-as-safe)-listed, and already included in the FDA Inactive Ingredients Database.
Dubbed Upsalite, the new material has potential uses in chemical catalysis, drug formulation and delivery, chemical and oil spill clean-up, and odor control.
The Uppsala team, under Maria Strømme, professor of nanotechnology and head of Nanotechnology and Functional Materials Division at the Ångström Laboratory, was attempting to synthesize anhydrous magnesium carbonate. Unlike other alkali earth metal carbonates, chemists have found anhydrous magnesium carbonate difficult to produce, particularly at low temperatures. The so-called "magnesite problem" has long posed a chemical conundrum; German scientists failed to crack the problem in 1908, followed by Russian failures in 1926 and 1961.
"In contrast to what has been claimed for more than 100 years in the scientific literature, we have found that amorphous magnesium carbonate can be made in a very simple, low-temperature process," says Johan Goméz de la Torre, researcher at the Nanotechnology and Functional Materials Division.
"One Thursday afternoon in 2011, we slightly changed the synthesis parameters of the earlier unsuccessful attempts, and by mistake left the material in the reaction chamber over the weekend. Back at work on Monday morning we discovered that a rigid gel had formed and after drying this gel we started to get excited," he adds.
More than a year of detailed materials analysis and fine-tuning of the experiment followed. One of the Uppsala researchers had to rely on his Russian language skills as some of the chemistry details necessary for understanding the reaction mechanism were available only in an old Russian PhD thesis.
"After having gone through a number of state-of-the-art materials characterization techniques, it became clear that we had indeed synthesized the material that previously had been claimed impossible to make," notes Strømme.
The most striking discovery, however, wasn't so much that they had produced the new material, but rather its properties. It turns out that Upsalite has the highest surface area measured for an alkali earth metal carbonate – 800m2/g.
"This places the new material in the exclusive class of porous, high-surface-area materials including mesoporous silica, zeolites, metal organic frameworks and carbon nanotubes," says Strømme.
In addition, the researchers found that the material was filled with empty pores all with a diameter smaller than 6 nm. This pore structure affords a unique way of interacting with the environment. For example, Upsalite absorbs more water at low relative humidities than the best materials presently available — the hydroscopic zeolites. At the same time, this property can be regenerated with less energy consumption than is currently required in similar processes.
This, together with other unique properties of the new material, is expected to pave the way for many new sustainable products in a number of industrial applications, concludes Strømme.
The discovery will be commercialized though the spin-out company Disruptive Materials (www.disruptivematerials.com) that has been formed by the researchers, with Uppsala University acting as the holding company.
Full results of the team's work appear in the July 17 issue of PLOS ONE, a peer-reviewed open-access journal.
Seán Ottewell is Chemical Processing's editor at large. You can e-mail him at email@example.com.