Upsalite: an absorbing discovery - novel material for water sorption

Materials World magazine
,
1 Sep 2013

A novel material, named upsalite, has been synthesised by researchers in Sweden that could have unrivalled surface area and water sorption abilities.

The extremely porous, amorphous, anhydrous magnesium carbonate (MgCO3) was discovered by researchers at the Nanotechnology and Functional Materials (NFM) group at Uppsala University. Previous attempts to synthesise the water-free disordered form of MgCO3 in the same way as other disordered carbonates have failed, but the team succeeded by changing the synthesis parameters slightly, allowing more time for the reaction to occur.

The team took a few grammes of magnesium oxide (MgO) powder and mixed it with methanol. The solution was then put under three-bar pressure of CO2 and heated to 50°C. The mixture was cooled to room temperature, the CO2 pressure was lowered to one bar and the reaction allowed to continue until a gel had formed. When dried in air at 70°C, the gel solidified and collapsed into a white powder.

The synthesis was carried out in 2011, but the team has since spent the intervening time characterising the material. Its amorphous anhydrous nature was confirmed using X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.

Also, to analyse the pore structure and water sorption capacity, the team carried out N2 and water vapour sorption analyses. They also used different types of electron microscopy and density functional theory to image and measure pore sizes and structures. The results of these studies show that the material has a surface area of about 800m2/g – the highest for any alkali earth metal carbonate – putting it in the same class as mesoporous silica and metal organic frameworks. The material is filled with empty pores less than 10nm in diameter and its water sorption capacity is about 50% greater than that of hydroscopic zeolites.

Professor Maria Strømme, Head of NFM Group, explains, ‘[Upsalite] can absorb more moisture at low humidities [up to about 60%] than any other known material, and these properties can be regenerated using less energy – at less than 100°C – than that needed for drying water-absorbing materials used industrially today’.

Strømme explains, ‘Upsalite is template-free, so no extra chemicals are needed for the synthesis that later need to be removed by other chemicals or heat.’

The material is now being commercialised through the University’s new Disruptive Materials spin-off company, which is assessing different manufacturing solutions and applications. One application is in de-humidifying industrial environments, either instead of, or as well as, established materials such as zeolites. Owing to its pore structure, Upsalite may also find use as a delivery method for amorphous drugs.

Commenting on the work, Professor Jason Riley, Director of Research in the Department of Materials at Imperial College London, UK, says the material shows an outstanding ability to reversibly adsorb water at low relative humidity. However, Riley adds, ‘The ratio of oxide to carbonate is not specified, and further work on the chemical composition of the material and the synthetic pathway is required to develop the material for industrial applications.’