ASSEMBLY OF MESOPOROUS LAMELLAR SILICAS WITH HIERARCHICAL PARTICLE ARCHITECTURES

A family of silica molecular sieves with lamellar frameworks and hiera rchical structure (denoted MSU-V) was assembled from homogeneous solut ions of neutral H2N(CH2)(n)NH2 bolaamphiphiles (n = 12-22) as the stru cture directors and tetraethylorthosilicate as the inorganic precursor . Optimal lamellar order was observed for four as-synthesized and calc ined (550 degrees C) mesostructures when they were assembled at the fo llowing reaction temperatures (T, degrees C) and surfactant/silica rat ios (R) of T = 25 degrees C, R = 0.26 (C-12); T = 45 degrees C, R = 0. 20 (C-16); T = 55 degrees C, R = 0.15 (C-18); T = 55 degrees C, R = 0. 11 (C-22) MSU-V silica assembled from the short C-12 alkyl chain bolaa mphiphile exhibited gallery-confined micropores (1.3 nm), but the deri vatives prepared from the longer C-16-C-22 diamines showed gallery-con fined mesopores. As the alkyl chain length of the bolaamphiphile surfa ctant increased from C-16 to C-22, the size of the gallery-confined me sopores increased from 2.0 to 2.7 nm, The described synthetic strategy afforded hierarchical MSU-V structures with biomimetic multilamellar vesicular particle architectures. Distorted vesicular, plate, and spir al-ribbon shaped particles also were observed, particularly for the la mellar silica assembled from the C-16 bolaamphiphile. The variation in morphologies was attributed to agitation effects during synthesis. MS U-V silica assembled from the C-22 diamine was the least stable member of the series and partially decomposed upon calcination. Remarkably, surfactant removal by calcination did not affect the biomembrane-like, hollow disk morphology of the original as-synthesized C-22 product. T his bolaamphiphile assembly approach provides new opportunities for th e preparation of tamellar mesoporous molecular sieves with hierarchica l structures specifically tailored to applications as diverse as sorbe nts, catalysts, sensors, bone implants, and nanoscale devices.