Ethylene-bridged Periodic Mesoporous Organosilica Nanoparticles: controlling architecture through mechanistic investigations

The synthesis of periodic mesoporous organosilica nanoparticles via the hydrolysis and condensation of 1,2-bis(triethoxysilyl)ethane (BTEE), with porosity templated by cetyltrimethylammonium bromide (CTAB) as surfactant and sodium salicylate (NaSal) as co-surfactant, has been investigated. In addition to the cubic alignment of spherical pores typically observed for such nanoparticles, the addition of NaSal prior to the initiation of BTEE hydrolysis led to the formation of nanoparticles with 2D hexagonal cylindrical pore geometry. By delaying the addition of NaSal until after the nucleation of nanoparticles with cubic porosity, multipodal nanostructures were obtained, in which the spherical cores exhibited cubic pore symmetry while the pods exhibited 2D hexagonal symmetry. All materials were carefully characterized by multiple techniques including SAXS, electron microscopy and gas physisorption experiments with N 2 and Ar as adsorbates. In particular, we showed that it is necessary to use quenched solid density functional theory (QSDFT) with appropriate kernels to correctly model the pore diameters, which were corrected from 2.8 nm with the incorrect but widely used BJH method to 4.8 nm with QSDFT in the case of spherical pores. The mechanism by which pores with different geometries evolved using a single organosilane precursor, together with the transition from spherical particles to multipodal systems following delayed addition of NaSal, was explored via conductivity, light scattering, and electron microscopy. These studies revealed that no additional growth of the cores occurred after addition of the NaSal, with the pods growing from small embryos initially formed at specific regions on the surface of the initially-formed cores.