Synthesis of Uniform Porous Silica Microspheres with Hydrophilic Polymer as Stabilizing Agent

Porous silica microspheres have wide applications in various areas. It has been a challenge to produce uniform silica microspheres with tunable pore size. In this study, uniform porous silica microspheres were synthesized using a modified Stöber method. Cetyltrimethylammonium bromide (CTAB) was used as a cationic surfactant to introduce ordered mesoporosity into silica spheres. Hydrophilic polymers poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), and poly(ethylene glycol) (PEG) were introduced into the reaction system. It was found that the use of PVA led to the formation of uniform and well-dispersed porous silica microspheres. The effect of the polymers on pore size and particles morphology was also studied. Another cationic surfactant dihexadecyldimethylammonium bromide (DiCTAB) and a nonionic surfactant (Brij-35) were further investigated by replacing CTAB. Uniform nonporous silica nanospheres were formed for Brij-35 and Brij-35/PVA systems. The use of DiCTAB resulted in submicrometer silica spheres with high surface area and larger pore size. The addition of PVA into the reaction system dramatically reduced the surface area and pore volume. The mesopores in the silica microspheres formed from the CTAB-PVA template were expanded using 1,3,5-trimethylbenzene and N,N-dimethyldecylamine as swelling agents by a hydrothermal method. The pore size was increased from 2.7 to 4.5 nm and 6.5 nm, respectively.