Dissolution behaviour of a nanoparticle in a microscale volume of solvent: thermodynamic and kinetic considerations

The dissolution behaviour of an oxidic nanoparticle in a small volume of solvent was investigated. The results of thermodynamic and kinetic calculations are presented. Variations in nanoparticle size and solvent volume are considered. Two kinds of final states of the system can be formed. One state is a homogeneous monomolecular solution of the dissolved species; the other one is a system in stable equilibrium between nanoparticle and solvent. What kind of state is formed depends on the size of the nanoparticle and the amount of solvent. The concentration of the dissolved species is much higher than the saturation concentration of the bulk material in many cases. An unusual dissolution behaviour of an ensemble of nanoparticles, called kinetic size effect, follows from the calculations. A very high concentration is found of the dissolved material at the beginning of the dissolution process. The concentration decreases at longer dissolution times. As an example, the experimental results of the dissolution kinetics of an ensemble of nanoparticles of commercial titanium dioxide in water are presented. Good agreement between experimental results and theoretical calculations is found. From these data it can be deduced that a nanoparticle with a radius of 14.15 nm dissolves in a volume of water of 18 microm(3) until its radius becomes 13.77 nm and a stable system nanoparticle-dissolved substance-solvent is formed (supersaturation 24), whereas a nanoparticle of radius 11.4 nm is completely dissolved after 73 h (supersaturation 165). The effect is established for different oxides.