Biomimetic calcium carbonate with hierarchical porosity produced using cork as a sustainable template agent

Calcium carbonate has many applications in different fields; its use in environment remediation is particularly considered, due to its non-toxicity and potentially high efficiency. The structure, morphology and surface features of calcium carbonate can greatly affect its performance. Hierarchical porosity, in particular, can be beneficial for several functional properties. In this study, we report the synthesis of biomorphic calcium carbonate using a sustainable template agent - waste cork powder. Pyrolysed cork powder was infiltrated by an appropriate calcium-containing salt and successively thermally treated. Selected precursors, different impregnation-solution concentrations and thermal conditions were tested. The resulting materials were characterised by XRD, Raman spectroscopy and SEM. Surface area and porosity features were studied by BET analysis, with a detailed study on the effect of synthesis on the mesoporosity of the materials, average sizes varying between 4-15 nm. The most valuable results were achieved with calcium acetate followed by pyrolysis performed for relatively short time period. This maintained the porous 3D honeycomb cork structure made of similar to 20 mu m hexagonal cells, while consisting of highly mesoporous single-phase CaCO3. Such samples showed the highest surface area ever reported for CaCO3 prepared using a plant-based template; moreover, it also exhibited a dual-scale hierarchical porosity as, in addition to micrometer scale cellular macroporosity, it contained a significant mesoporosity in the cell walls, with a very narrow range of 3.6-3.9 nm.