Room-Temperature Synthesis of Hollow Polymer Microparticles with an Open Hole on the Surface and Their Application

Compared with hollow microparticles with a completely closed shell structure, hollow polymer microparticles with an open hole on their surface have attracted considerable attention because of the obvious importance of the open hole on their surface; however, the development of a facile method to synthesize such unique open-ended hollow particles has remained a great challenge. In this study, an easy-to-use method was developed to rapidly produce monodispersed hollow and pored microparticles in high reaction yield at room temperature. The key to achieving the unusually shaped polystyrene (PS) microparticles was the use of anisotropic PS seeds. When hollow and dimpled PS seeds prepared using a modified dispersion polymerization method were dispersed in a water-toluene mixture followed by solvent evaporation under ambient conditions, they transformed into hollow PS microparticles with an open hole on their surface. A plausible mechanism for the transformation of the PS microparticles during the swelling and drying processes was proposed on the basis of our results and observations. The structural features of the hollow and pored PS microparticles motivated us to use the particles as a catalyst support. By using modified heterophase polymer dispersion processing involving the addition of a Ag precursor, hollow and pored PS microparticles covered with Ag nanocrystals were obtained on the basis of the in situ reduction of metal precursor on the surface of polymer particles. The resulting Ag nanocrystals/PS hybrid microparticles exhibited enhanced catalytic activity at low concentrations of nanocrystals and could be reused several times without loss of activity when used as catalysts for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride.