Figure 1.
Characterisation of as-synthesised Upsalite and schematic description of the synthesis steps.
a) XRD pattern. The halo at 2 θ∼30° indicates the presence of at least one amorphous phase and the sharp peaks at higher scattering angles pertain to crystalline MgO. b) Raman spectrum. The band observed at ∼1100 cm−1 stems from vibration of the CO3 group and the halo cantered at 100 cm−1 is a Boson peak. c) FTIR spectrum. The three visible absorption bands (1440 cm−1, 1100 cm−1 and 850 cm−1) are all due to vibrations of the CO3 group. d) and e) XPS Mg2p and O1s peaks. The Mg2p peak at 52.1 eV and the O1s peak at 533.5 eV stem from MgCO3, the O1s peak at 531.0 eV from MgO and the O1s peak at 535.6 eV from surface adsorbed water. The solid lines represent the measured spectrum. The coloured lines are calculated using the CasaXPS software and represent the fitted curves (obtained using Gaussian-Lorentzian functions) and the subtracted background (obtained using a Shirley function).
Figure 2.
i) In the first step MgO (s) is mixed with methanol under 3 bar CO2 pressure at 50°C. ii) After 2.5 h the HOMgOCH3 is formed in the solution, the pressure is lowered to 1 bar and the heating is turned off. At the same time the methanol reacts with the CO2 and forms CH3OCOOH (methyl hemicarbonic acid). iii) HOMgOCH3 reacts with CH3OCOOH and forms water and H3COCOOMgOCH3 (methyl esther of magnesium methyl carbonate). At this point the solution changes colour from white to light yellow. iv) H3COCOOMgOCH3 reacts with the water formed in step iii) and forms HOMgOCOOCH3 (or MgCO3·CH3OH) which upon v) heating at 70°C releases CH3OH and forms MgCO3.
Figure 3.
Sorption isotherms and DFT-based pore size distribution for Upsalite.
a) N2 sorption isotherm at 77 K. b) Incremental pore volume (violet) and cumulative pore volume (blue) obtained from N2 sorption isotherm. c) Moisture sorption isotherm at room temperature for Upsalite (blue), Mg5(CO3)4(OH)2·4H2O (green), Aerosil (red) and Zeolite Y (black). The arrows indicate the direction of the pressure change.
Table 1.
Structural and chemical characteristics of Upsalite obtained from N2 and H2O vapour sorption isotherms.
Figure 4.
Electron microscopy images of Upsalite.
a) SEM micrograph of Upsalite. Scale bar, 1 µm. b) Higher magnification SEM of a region in a) clearly showing the textural porosity of the material. Scale bar, 200 nm. c) Representative TEM image of Upsalite showing contrast consistent with a porous material. The image is recorded with under-focused conditions to enhance the contrast from the pores. Scale bar, 50 nm.