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.
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. 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)