The powder was simply placed on a clean glass slide for optical microscope
observation, but to avoid damage during SEM imaging, the
powder was carefully attached to an aluminium specimen holder
using a conducting adhesive and sputter-coated with a 100 ˚A thick
gold. The specific surface area and pore size were determined by
nitrogen physisorption (Coulter SA 3100), while the particle size
and surface charge were measured by Zetaplus from Brookhaven
Instruments Corp. Ten milligrams of powder sample was dispersed
in 20mLdeionized, distilled water and 5mL suspension was
measured in a sample cell designed to eliminate electroosmotic
effects.