All the chemical reagents were purchased from Fisher Scientific if
not specifically noted. Egg shells were collected from eggs sold by
Wal-Mart. Nanosilica was in a colloidal form (NexSil 125k, Nyacol
Nano Technologies) and detailed information is shown in Table 1.
The surfaces of the collected egg shells were mechanically cleaned
using ultra-sonication. They were subsequently calcined at 900 °C for
3 h to completely burn out organic materials and convert the major inorganic
component CaCO3 into CaO. After the powder cooled down, the
calcined materials were crushed and ground in an agate mortar to get a
fine powder (calcined egg shell). The synthesized powder was incubated
in deionized (DI) water and then followed by filtering to convert the
synthesized CaO into fine Ca(OH)2 powder. This was also done to remove
trace soluble salts from the powder. The prepared raw powder
was dried at 60 °C in an oven for 24 h