A solvent contains nanoparticles which have a primary particle diameter of less than 100nm and to which a surface modifying agent is bonded and fixed, and a compound not bonded and fixed to the surface of the nanoparticles. In a supercritical state, this solvent is contacted with a trap material such as dummy particles larger than the nanoparticles, and compounds contained in the solvent and not bonded and fixed to the surface of the nanoparticles are trapped by the trap material and removed.
展开▼
