Surface properties of submicrometer silica spheres modified with aminopropyltriethoxysilane and phenyltriethoxysilane.

The surface of submicrometer silica spheres are modified with aminopropyl and phenyl groups through a one-step process. Various experimental techniques, i.e., scanning electron microscopy (SEM), quasi-elastic light scattering (QELS), differential scanning calorimetry (DSC), thermogravimetry (TG), zeta potential measurement, nitrogen sorption, and water vapor and organic dye adsorption are used to comprehensively characterize the pure (TEOS particles) and modified silica particles. The SEM micrographs of the particles demonstrate that the modified particles are spherical with uniform size and shape. The particles modified with aminopropyl groups (APTES particles) show the highest isoelectric point (IEP) and the highest weight loss at 780 degrees C because of the basic nature of aminopropyl groups and the higher reactivity of aminopropyltriethoxysilane. The particles modified with the phenyl groups (PhTES particles) show the lowest water vapor adsorption because their surface is more hydrophobic than that of TEOS and APTES particles. The organic dye (brilliant blue FCF or BBF) adsorption experiments demonstrate that the adsorption capacity of the particles increases greatly after acidification. This is caused by the protonation of silanol groups and amine groups on the particle surface, which presents an enhanced electrostatic attraction with BBF anions. The APTES particles exhibit the highest dye adsorption due to the hydrophobic attractions and the enhanced electrostatic attractions from aminopropyl groups.