Template-assisted synthesis of MgO promoted CaO

“As illustrated schematically in Fig. 1, the hydrothermal treatment of an aqueous solution of xylose, urea, and glycine together with Ca and Mg precursors at 180 °C for 24 h yielded micron-sized carbonaceous spheres that encapsulate homogeneously Ca2+ and Mg2+ species. The simultaneous hydrolysis of urea led to a gradual rise in the pH resulting in the precipitation of CaCO3 and MgCO345,46,47. EDX analysis of FIB cross-sections of the as-synthesized material (Supplementary Fig. 1) confirms the homogeneous distribution of Ca and Mg within the carbonaceous template, a rather surprising observation. The presence of glycine in the precursor solution yields complexes of Ca2+ and Mg2+ which improves the homogeneity of the precipitated CaCO3 and MgCO3 structures48. Xylose was preferred over alternative biomass precursors (e.g., glucose or sucrose), since hydrothermally treated pentoses (e.g., xylose) were shown to yield highly dispersed carbonaceous spheres, whereas the hydrothermal treatment of hexoses (e.g., glucose) resulted typically in an interconnected network of carbonaceous spheres49. Calcination of the materials in air at 800 °C resulted in the complete removal of the carbonaceous template and the formation of highly porous, multishelled microspheres, whereby the shells are composed of CaO and MgO nanoparticles. It is noteworthy that all of the compounds utilized in the synthesis of the sorbents are relatively inexpensive and environmentally benign as opposed to other commonly used template-assisted approaches that involve, e.g., resorcinol/formaldehyde-derived templates50.”


“Synthesis protocol. Schematic illustration of the hydrothermal approach developed here to synthesize template-assisted, MgO-stabilized, CaO-based CO2 sorbents”

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