In this study, highly monodisperse cyanoethyl-/cyanopropyl-functionalized silica micro/nanospheres (CN-E-SiO2/CN-P-SiO2) have first been synthesized via one-pot sol–gel reaction at room temperature in the microemulsion system. Effects of the surfactant concentrations and the reaction time on the formation of CN-E-SiO2/CN-P-SiO2 have been discussed. Furthermore, bifunctional core–shell structures prepared using CN-E-SiO2 and CN-P-SiO2 as core and ureidopropyl-functionalized silica spheres (UD-SiO2) as shell, denoted as CN-E-SiO2@UD-SiO2 and CN-P-SiO2@UD-SiO2, have also been etched separately in alkaline conditions. Compared with the original CN-E-SiO2 and CN-P-SiO2, transmission electron microscopy images showed that the diameter of CN-E-SiO2@UD-SiO2 and CN-P-SiO2@UD-SiO2 core–shell structures was all reduced during etching in alkaline condition, finally resulting in a hollow structure with a similar sphere size. In addition, for the sake of comparison, pure silica as core and UD-SiO2 as shell, denoted as SiO2@UD-SiO2 core–shell structure, has also been prepared. However, transmission electron microscopy image indicated that the size and shape of SiO2@UD-SiO2 was almost unchanged in the whole etching process. It can be proved that selective etching of bifunctional core–shell organosilica is an optimal strategy for preparation of hollow materials.
Graphical Abstract