Macroscaled mesoporous calcium carbonate tetragonal prisms: top-down solid-phase fabrication and applications of phase-change material support matrices

Abstract

In this article, we have demonstrated top-down solid-phase transformation from calcium oxalate dehydrate (COD) tetragonal prisms into highly macroscaled mesoporous calcium carbonate tetragonal prisms. Also, being a promising C₂O₄²⁻ source, L-ascorbic acid (AA) was first applied to obtain high-quality COD tetragonal prisms. The high crystal quality of COD is critical for the successful fabrication of porous CaCO₃ microcrystals with predetermined morphology and well-controlled internal structure. Calcined at different heating rates, porous CaCO₃ with different pore sizes was obtained. This novel, simple thermal transformation strategy is convenient for preparing nanoporous materials at a large scale, and it is also useful to further extend to convert salt carbonate into such porous nanostructures. The as-obtained porous CaCO₃ tetragonal prisms are nontoxic, cheap and environmentally friendly, and the application of such porous CaCO₃ with different pore sizes as support matrices successfully mitigates the common problems for phase-change materials (PCMs) of inorganic salts, such as phase separation phenomena and super-cooling effect. Our experiments clearly reveal that the confinement effect of the porous structure plays a more dominant role in mitigation of the phase separation while the mesoporous CaCO₃ microcrystals with the smaller mesopore sizes used PCMs as supporters. However, heterogeneous nucleation will be responsible for the mitigation of the phase separation in the macroporous CaCO₃ support matrix, while in this case, size confinement effect is negligible. Thereby, the designed porous nanostructures can bring significant improvements to the heat-storage performance in future “smart house” wall materials.