A Template-Free, Ultra-Adsorbing, High Surface Area Carbonate Nanostructure

PLOS ONE, Dec 2019

We report the template-free, low-temperature synthesis of a stable, amorphous, and anhydrous magnesium carbonate nanostructure with pore sizes below 6 nm and a specific surface area of ∼ 800 m2 g−1, substantially surpassing the surface area of all previously described alkali earth metal carbonates. The moisture sorption of the novel nanostructure is featured by a unique set of properties including an adsorption capacity ∼50% larger than that of the hygroscopic zeolite-Y at low relative humidities and with the ability to retain more than 75% of the adsorbed water when the humidity is decreased from 95% to 5% at room temperature. These properties can be regenerated by heat treatment at temperatures below 100°C.The structure is foreseen to become useful in applications such as humidity control, as industrial adsorbents and filters, in drug delivery and catalysis.

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A Template-Free, Ultra-Adsorbing, High Surface Area Carbonate Nanostructure

High Surface Area Carbonate Nanostructure. PLoS ONE 8(7): e68486. doi:10.1371/journal.pone.0068486 A Template-Free, Ultra-Adsorbing, High Surface Area Carbonate Nanostructure Johan Forsgren 0 1 Sara Frykstrand 0 1 Kathryn Grandfield 0 1 Albert Mihranyan 0 1 Maria Strmme 0 1 Richard G. Haverkamp, Massey University, New Zealand 0 Current address: Department of Materials Science and Engineering, McMaster University , Hamilton , Canada 1 1 Division for Nanotechnology and Functional Materials, Department of Engineering Sciences, The A ngstro m Laboratory, Uppsala University , Uppsala , Sweden , 2 Division for Applied Materials Science, Department of Engineering Sciences, The A ngstro m Laboratory, Uppsala University , Uppsala , Sweden We report the template-free, low-temperature synthesis of a stable, amorphous, and anhydrous magnesium carbonate nanostructure with pore sizes below 6 nm and a specific surface area of , 800 m2 g21, substantially surpassing the surface area of all previously described alkali earth metal carbonates. The moisture sorption of the novel nanostructure is featured by a unique set of properties including an adsorption capacity ,50% larger than that of the hygroscopic zeolite-Y at low relative humidities and with the ability to retain more than 75% of the adsorbed water when the humidity is decreased from 95% to 5% at room temperature. These properties can be regenerated by heat treatment at temperatures below 100uC.The structure is foreseen to become useful in applications such as humidity control, as industrial adsorbents and filters, in drug delivery and catalysis. - . These authors contributed equally to this work. Nanotechnology is starting to influence most scientific areas and this key enabling technology is foreseen to significantly impact all materials science dependent industries during the coming decades [14]. The interest in high surface area nanostructured materials from 1990 onwards has increased exponentially for all classes of porous materials and at the beginning of 2013, according to the ISI Web of Knowledge, there were in total about 60,500 records on zeolites, 20,500 records for mesoporous silica and 13,100 records on metal organic framework (MOF) materials, whereas before 1990 these numbers were insignificant. The most common way to produce high surface area materials with micro-mesoporous structures, i.e., pores with diameters below 50 nm, is by using soft templates and building around them a more rigid structure after which the template is eluted with a solvent or burnt away to produce the rigid porous material. In the current work we will show that it is possible, at low temperatures and without the use of templates, to synthesize a unique high surface area nanostructure with a well-defined poresize distribution of sub 6 nm pores of a widely used, non-toxic and GRAS (generally-recognised-as-safe)-listed material that is already included in the FDA Inactive Ingredients Database [5]; viz. magnesium carbonate. Magnesium is the eighth most abundant element in the earths crust and essential to most living species. It can form several structures of hydrated carbonates such as nesquehonite (MgCO3?3H2O), and lansfordite (MgCO3?5H2O), a number of basic carbonates such as hydromagnesite (4 MgCO3?Mg(OH)2?4 H2O), and dypingite (4 MgCO3?Mg(OH)2?5 H2O), as well as the anhydrous and rarely encountered magnesite (MgCO3) [5]. In contrast to other alkali earth metal carbonates, chemists have found anhydrous magnesium carbonate difficult to produce, particularly at low temperatures. Above 100uC, magnesite (crystalline MgCO3) can be obtained from Mg(HCO3)2 solutions by precipitation. However, at lower temperatures, hydrated magnesium carbonates tend to form, giving rise to what has been referred to as the magnesite problem [6].Yet, not only chemists have been intrigued by magnesium carbonates. Although abundant in nature, where crystalline forms exist as traces in most geological structures, pure magnesium carbonate is seldom found on its own in larger deposits, a fact that has puzzled geologist for more than a century [7]. In 1908, Neuberg and Rewald tried to synthesise magnesite in alcohol suspensions of MgO [8]. However, it was concluded that MgCO3 cannot be obtained by passing CO2 gas through such suspensions due to the more likely formation of magnesium dimethyl carbonate (Mg(OCOOCH3)2). Subsequent studies by Kurov in 1961 [9] and Buzagh in 1926 [10] only reiterated the assumption that MgO preferentially forms complex dimethyl carbonates when reacted with CO2 in methanol. A further overview of early works is provided in detail in Text S1 and Figure S1. Yet, by changing the synthesis conditions in comparison to what has been described earlier, we here report the successful formation of a magnesium carbonate, hereafter referred to as Upsalite, in a reaction between MgO, methanol and CO2 resulting in an anhydrous, micro-mesoporous and large surface area structure. We fu (...truncated)


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Johan Forsgren, Sara Frykstrand, Kathryn Grandfield, Albert Mihranyan, Maria Strømme. A Template-Free, Ultra-Adsorbing, High Surface Area Carbonate Nanostructure, PLOS ONE, 2013, Volume 8, Issue 7, DOI: 10.1371/journal.pone.0068486