Development and characterization of mesoporosity in eggshell ground by planetary ball milling

A spent eggshell has been mechanically treated by a planetary ball mill under various conditions. Under the experiments investigated, rotational speed, grinding time and sample mass loading are three important operating parameters. The results showed that the resulting powders are type IV with hysteresis loops corresponding to type H3 from their nitrogen adsorption/desorption isotherms, indicating slit-shaped mesoporous characteristics. Under the optimal conditions, the ground eggshell powder has larger BET surface area (21.2 m2/g vs. 0.5 m2/g) than the starting eggshell. In addition, this study clearly demonstrated that the intensity of X-ray diffraction is on the decrease with the pore properties of the resulting eggshell powders, showing that the structure of the crystalline eggshell can be transformed into an amorphous one due to the decrease of the crystallite (calcite) sizes. Thus, the approach to create the porous network developed in eggshell agrowaste by high-energy ball milling offers a novel method in the preparation of mesoporous materials, which may be further applied in the fields of biomaterials.