Surfactant-free fabrication of SiO2-coated negatively charged polymer beads and monodisperse hollow SiO2 particles

Abstract

Abstract SiO2 coating on the surface of negatively charged polymer beads (n-PBs) succeeded in a typical Stober process with tetraethyl orthosilicate (TEOS). The core–shell structure of the resulting particles was confirmed by TEM observation and EDS mapping. Hollow SiO2 particles (HSPs) with monodisperse size and high dispersibility were further fabricated by calcining the obtained SiO2-coated n-PBs in air at 600 °C. Two advantages of using n-PBs for the fabrication of SiO2-coated polymer beads and HSPs were revealed as (1) lower cost with respect to positively charged polymer beads (p-PBs) and (2) improving the dispersibility of the obtained HSPs. According to our observations, there are two prerequisites for the formation of SiO2 shells on n-PBs, as (1) the high surface charge density of n-PBs and (2) low water concentration in reaction system. A mechanism was proposed for explaining the coating of SiO2 on the like-charged polymer beads. In that mechanism, the adsorption of NH4+ ions on the surface of n-PBs played a critical role for SiO2 coating, as it not only screened the surface charge of n-PBs to reduce the energetic barrier for SiO2 deposition, but also caused the accumulation of OH− ions to restrict the location where SiO2 nucleated to the surface of n-PBs.