Anion Assisted Synthesis of Large Pore Hollow Dendritic Mesoporous Organosilica Nanoparticles: Understanding the Composition Gradient

A facile anion assisted approach to prepare dendritic hollow mesoporous organosilica nanoparticles (DHMONs) with a large pore size of 29.5 nm was reported. DMONs were prepared in an aqueous solution using tetraethyl orthosilicate (TEOS) and 1,2-bis(triethoxysilyl)- ethane (BTEE) as precursors, triethanolamine as a catalyst, cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) as structure-directing agents. Electron tomography (ET) was used to further investigate the structure. An ET slice cutting across the center of one DMON particle reveals a central core with a diameter of 80 nm and radial pore opening of 16 nm. After alkaline etching of DMONs using 0.6 M NaCO at 60°C for 4 h, monodispersed DHMONs with similar size to DMONs of 200 nm can be obtained as shown by SEM image. TEM image reveals that DHMONs possess a shell with radial pore channels and an inner hollow cavity. The ET slice clearly confirms the hollow nature of DHMONs. By comparing the SEM, TEM, ET and NMR results together, it is clear that DMONs have a composition gradient