Chitosan-Catalyzed Aggregation during the Biomimetic Synthesis of Silica Nanoparticles

Silicate is polymerized in the presence of chitosan to form novel silica−chitosan nanoparticles in weakly acidic solution under ambient conditions. Both the turbidity of the silica solution and the average hydrodynamic diameter of the silica nanoparticles increased dramatically after the addition of chitosan. The initial stage of silica formation closely observed fourth-order kinetics. The latter transformation of colloidal nanoparticles approximated an exponential growth pattern during slow aggregation. Chitosan did not significantly change the rate of silica synthesis and the size of the individual nanoparticles, but it facilitated an aggregation of the composite nanoparticles by 1 order of magnitude faster than for pure silica nanoparticles. Scanning electron microscopy revealed that the composite nanoparticles grew in three dimensions and became clusters and aggregates within a shorter time. Atomic force microscopy demonstrated that the composite nanoparticles increased from as small as 1 nm to 32 nm after a reaction time of 1 and 24 h, respectively. X-ray diffraction, infrared spectroscopy, and elemental analysis confirmed that these nanoparticles were amorphous composites of silica and chitosan. Synthesis of silica with chitosan provided a facile way of preparing composite silica nanoparticles with improved functional properties.