1. Introduction
Surface modification is an effective way to improve dispersibility
of nano crystalline solids in organic or inorganic solvents. Function alization
by organic compounds may be used to increase the
dispersibility in liquids and formation of stable colloidal solutions,
but also to improve compatibility with solids, e.g., polymer
matrices [1]. Physical properties of particles in suspensions
strongly depend on charge distribution and ionic structure at the
particle–solvent interface [2,3]. Aggregation of nanoparticles, as a
spontaneous process, must be hindered to keep the system in the
form of a stable transparent colloid. Considering photocatalytic
systems, the activity of a photo catalyst in forms of separated nanoparticles
and aggregates differs significantly. An extended aggregation
reduces the active surface of materials and leads to a poorer
interfacial electron transfer efficiency and a low substrate accessibility
[4]. The ability of nanoparticles to penetrate tissues and cells
should also be taken into account when medical applications of
photocatalysts are considered. On the other hand, a facile electron
transfer between aggregated nanocrystals may prevent recombination
and prolong lifetimes of photo generated charges [5].