Chiral Mesoporous Silicals Templated By Anionic Surfactant

The highly ordered chiral mesoporous silica have attracted much interest in the chemistry and material communities because of their helical pore structure, high surface areas, large pore volume and tailorable pore size. It is thought to have great application potentiality in selective adsorption and separation, synthesis of chiral nano materials, and asymmetric catalysis. However, there are still a lot of problems to solve in this new field. In this thesis,the synthesis of the chiral mesoporous silica, the mechanism of such synthesis and the factors of chiral mesoporous silica will be discussed. There are four parts in this thesis:In chapter 1, the basic character of chiral materials and organinc chiral material including chiral supramolecular assembling and chiral liquid crystal were firstly reviewed. Then, the synthesis mechanism of inorganic materials and the current studies on the chiral mesoporous materials were reviewed.In chapter 2, chiral ordered mesoporous silica was synthesized by using chiral surfactant N-myristoyl-L-alanine sodium salt (C14-L-AlaS) as template, 3-aminopropyltriethoxysilane (APES) as co-structure directing agent (CSDA) and tetraethoxylsilane (TEOS) as inorganic source. The morphology and chiral structure clearly depend on the stirring rate. When the stirring rate is lower than 300 rpm the samples show diverse morphologies: twisted ribbon like and various twisted rod like structures with different chiral pitches. The morphologies become uniformly twisted rod with a hexagonal cross-section when the stirring rate is increased to 400 rpm, 600 rpm and 800 rpm. The samples synthesized at rate faster than 1200 rpm showed non-helical morphology. The outer diameter of rod was increased with increasing stirring rate and the pitch length was also increased with increasing of the rod diameter with constant pitch/rod diameter ratio of ~15.5. It can be considered that the same 2d-hexagonal p6mm structure with the same pore size and wall thickness has been formed regardless of the stirring rate. The left-/right-handedness ratio is proved to be ca. 7.5/2.5 for the total samples regardless of the difference in stirring rate or direction as far as the rate is faster than 400 rpm.In chapter 3, using lipids (N-acyl amino acid) and APES as structure and costructure directing agents, mesoporous silicas with four different morphologies, that is helical ribbon (HR), hollow sphere, circular disc and helical hexagonal rod were synthesized only by changing synthesis temperature from 0 to 10, 15 and to 20°C. Their structures were studied by electron microscopy. It has been found that (i) they have structures double-layer disordered mesopores in HR and radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2d-hexagonal mesopores in the disk-like and helical rod, respectively; (ii) these four types mesoporous silicas were transformed from the flat bilayered lipid ribbon with the chain-interdigitated layer phase through solid-solid transformation for HR formation and dissolving procedure transformation for hollow sphere, circular disc and twisted morphologies, respectively; (iii) the mesoporous silica helical ribbon was exclusively right-handed and the 2d-hexagonal chiral mesoporous silica was left-handed excess when L form N-acyl aminoacid has been used as lipid template; (iv) the HR has been formed only by the chiral lipid molecules and the 2d-hexagonal chiral mesoporous silicas have been formed chiral, achiral and racemic lipids.In chapter 4, chiral mesoporous silica with highly ordered helical nano-sized channels was synthesized by using chiral anionic amphiphilic molecules (N-acyl-L-alanine) as template upon a CSDA method. Synthetic conditions, such as ionization degree of the surfactant, CSDA/surfactant molar ratio, reaction temperature, the carbon chain length, and the type of counterions have been extensively studied. It was found that: (i) in the synthesis-space diagram of mesophases, the CMS mesostrucrue locates within the area of two dimensional (2D-) hexagonal which is a neighbor of lamellar and bicontinuous Ia3d mesostructures; (ii) the generation of CMS demands very rigorous micellar curvature which was mainly controlled by the ionization degree of the surfactant controlled by acid addition amount, CSDA/surfactant molar ratio and the carbon chain length; (iii) the CMS can be synthesized in a wide reaction temperature range of 25-100 oC; and (iv) the pore diameter of the CMS was decreased with decreasing size of the counterion.