Surfactant Mediated Control of Pore Size and Morphology for Molecularly Ordered Ethylene-Bridged Periodic Mesoporous Organosilica

A series of ethylene-containing mesoporous organosilica materials were fabricated via surfactant-mediated assembly of 1,2-bis(triethoxysilyl)ethylene (BTEE) organosilica precursor using alkyltrimethylammonium bromide (C_nTAB) surfactants with different alkyl chain length (n = 12, 14, 16, 18) as supramolecular templates. The presence of molecularly ordered ethylene groups in the resulting periodic mesoporous organosilica (PMO) materials was confirmed by XRD data along with ²⁹Si and ¹³C MAS NMR analysis. Additional characterization techniques, namely nitrogen sorption, TEM, and TGA, confirmed the structural ordering and thermal stability of the molecularly ordered ethylene-bridged PMOs. The PMOs exhibit molecular-scale ordering (with a periodicity of 5.6 Å) within the organosilica framework and tunable pore size, which depending on the alkyl chain length of the surfactant templates, varied in the range 23−41 Å. Furthermore, depending on the alkyl chain length of the templates, the particle morphology of the PMOs gradually changed from monodisperse spheres (for C₁₂TAB) to rod or cakelike particles (for C₁₄TAB) and elongated ropelike particles for longer chain surfactants. Variations in the surfactant chain length therefore allowed control of both the pore size and particle morphology without compromising molecular-scale or structural ordering. The reactivity of ethylene groups was probed by bromination, which demonstrated the potential for further functionalization of the PMOs.