The methods for making nanoparticles can generally involve
either a “top down” approach or a “bottom up” approach (Sepeur,
2008). In top-down synthesis (Fig. 1), nanoparticles are produced
by size reduction from a suitable starting material (Meyers et al.,
2006). Size reduction is achieved by various physical and chemical
treatments (Fig. 1). Top down production methods introduce imperfections
in the surface structure of the product and this is a major
limitation because the surface chemistry and the other physical properties
of nanoparticles are highly dependent on the surface structure