The two silica sources used for the synthesis of MPS were MicroPS derived from kaolinite, and TEOS (Si(OC2H5)4).
The MicroPS was prepared from kaolinite (Al2Si2O5(OH)4;Inagaki Mining) obtained from Georgia, USA. This was
calcined at 600 C for 24 h to form the anhydrous X-ray amorphous phase metakaolinite, then acid-leached. Calcination
is necessary because kaolinite resists leaching, even under highly acidic conditions [8]. The metakaolinite was leached in 2.5 M H2SO4 solution at 90 C for 3 h with stirring. These leaching conditions give an optimal SBET value of the resulting MicroPS. After leaching, the product was washed with dilute H2SO4 (0.5 M), washed three times
with deionized water and centrifuged. The Si/Al ratio of the resulting MicroPS was 41 and its SBET value was 370 m2/g, arising from slit-shaped micropores 0.6 nm wide[8]. The second silica source was reagent grade TEOS
(Wako), used without pre-treatment.