Selective etching of bifunctional core–shell organosilica micro/nanospheres to hollow structures

In this study, highly monodisperse cyanoethyl-/cyanopropyl-functionalized silica micro/nanospheres (CN-E-SiO 2 /CN-P-SiO 2 ) 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-SiO 2 /CN-P-SiO 2 have been discussed. Furthermore, bifunctional core–shell structures prepared using CN-E-SiO 2 and CN-P-SiO 2 as core and ureidopropyl-functionalized silica spheres (UD-SiO 2 ) as shell, denoted as CN-E-SiO 2 @UD-SiO 2 and CN-P-SiO 2 @UD-SiO 2 , have also been etched separately in alkaline conditions. Compared with the original CN-E-SiO 2 and CN-P-SiO 2 , transmission electron microscopy images showed that the diameter of CN-E-SiO 2 @UD-SiO 2 and CN-P-SiO 2 @UD-SiO 2 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-SiO 2 as shell, denoted as SiO 2 @UD-SiO 2 core–shell structure, has also been prepared. However, transmission electron microscopy image indicated that the size and shape of SiO 2 @UD-SiO 2 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