Facile preparation of size-controlled mesoporous silica particles by metal-chelating surfactant micelle complexes

The size-controlling of mesoporous silica particles (MSPs) are achieved by various metal-chelating surfactant micelle complexes using alkali (Na+, K+, and Cs+), alkaline earth (Mg2+, Ca2+, Sr2+, and Ba2+), and transition metal ions (Co2+, Ni2+, Cu2+, and Zn2+), respectively. These metal ions form a metal-surfactant micelle complex in an aqueous solution, while the metal ions are chelated to the hydrophilic domain of the surfactant such as the poly(ethylene oxide) group of a P123 surfactant. The differences in the complexation degree between the metal ions and surfactant plays an important role in determining the formation of nano-sized ordered MSPs due to the different stability constant for metal-P123 surfactant complexation. The complete hydrolysis of a silica precursor under an acidic condition and the subsequent steady assembly of negative silicate species and positive metal ions can effectively improve highly ordered MSPs. Consequently, the particle size can be reduced from a particle length of 1700 nm to a range of 250-800 nm with the transition metal ions.