Preparation of Colloidal Mesoporous Silica Nanoparticles with Different Diameters and Their Unique Degradation Behavior in Static Aqueous Systems

The degradation of colloidal mesoporous silica nanoparticles (CMPS) is quite important for the design of stable catalyst supports and biodegradable drug delivery systems carriers. The degradation of various silica nanoparticles in static aqueous systems was investigated. The condition was achieved through the use of a dialysis tube. Four types of CMPS with different particle diameters (ca. 20-80 nm) were newly prepared from tetraalkoxysilanes (Si(OR)(4), R = Me, Et, Pr, and Bu) at different hydrolysis rates by a one-pot synthesis. Larger particles were formed by using tetraalkoxysilanes at slower hydrolysis rates because particle growth dominates nucleation. The degradation of CMPS is independent of diameter differences. The degradation rate of CMPS is higher than that of colloidal nonporous silica nanoparticles with smaller diameters because of the presence of mesopores. CMPS are also more degradable than aggregated CMPS because of colloidal clispersity. Moreover, it was confirmed for the first time that the degradation simultaneously proceeds from the outer as well as the inner surfaces of CMPS and that the mesostructure and morphology are partly retained even after more than half of the CMPS are degraded. The information on the degradation reported here is quite useful for the design of silica-based nanomaterials with tunable degradability/stability.