Xiuzhi Wang

Highly hydrophobic mesoporous materials as matrix for gas chromatography separation of water-alcohols mixtures

In this chapter, the hydrophobic mesoporous materials are synthesized and investigated as gas chromatography (GC) stationary phase for the separation of complicated water-alcohol systems. The hydrophobic mesoporous materials show high resolution and efficiency for the tested systems. The matrix achieves base-line separation of the propanol isomers via their different Van Der Waals interactions with functionalized surfaces in nanochannel. The chapter illustrates the representative transmission electron microscopy (TEM) image of the sample. It depicts a direct image of the 3D wormhole-like pore frameworks. The obtained hybrids are grinded and tabletted to measure the hydrophobicity. The N2 adsorption/desorption isotherms illustrate that the sample exhibits type IV isotherm with type H2 hysteresis loop, which further confirms the mesoporous sturcture of the samples. The hydrophobic materials exhibit the high resolution and efficiency for the water-alcohol mixtures. The separation order is highly consistent with the polarity of alcohol and water.

06-P-10 - Formation of double-mesopore silica and its transformatoin into MCM-41

Publisher Summary This chapter discusses the formation of double-mesopore silica and its transformation into MCM-41. The influence of alkali/silica molar ratio in the synthesis of mesoporous molecular sieve materials is studied in a simple synthesis system containing tetraethylorthosilicate, water, alkali, and cetyltrimethylammonium bromide at room temperature. The resulting silicate materials are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption–desorption isotherms. The results suggest that the formation of different surfactant-silicate aggregation array morphology not only relies on an interaction between silicate ions and the surfactant but also on a proportion of the silicate species to surfactant.

Separation of benzene and its relatives by highly hydrophobic microporous/mesoporous materials

A series of highly hydrophobic materials with different pore sizes were synthesized by non-surfactant route and then used as gas chromatography matrix for the separation of benzene and its relatives. So-produced materials with meso or micro/meso pores showed a high separation performance for the benzene and its relatives, and the highly hydrophobic microporous/mesoporous materials were shown to be good candidates for stationary phases for the separation of benzene and its relatives due to their high surface areas and highly thermal stability.

Compositional effects of bimodal mesopore silica synthesized by a base- catalyzed ambient pressure sol-gel processing

Abstract The effects of tetraethylorthosilicate (TEOS) concentration and TEOS/surfactant molar ratio on the synthesis of bimodal mesopore silica (BMS) were studied. It was found that the BMS silica can be synthesized in a wide range of component concentration and its secondary mesopore size is more sensitive to the change of precursor concentration than its primary mesopore size and the secondary mesopore volumes can be up to 2.0 or more times as large as the primary mesopore volumes. The controllability of the bimodal mesopore size distributions, in particular the secondary mesopore size of BMS silica is of great interest to catalysis because they greatly facilitate mass transport to the primary mesopore.

Structural and textural evolution of bimodal mesopore silica xerogels during aging and drying

Abstract The effects of aging and drying conditions on the structural and textural properties of surfactant-templated silica xerogel with bimodal mesopore distribution characteristic (designated as BMS) prepared under base-catalyzed sol-gel process were investigated. It was found that the change of aging and drying conditions would influence not only the size and the packing geometry of surfactant-encapsulated silica primary particles, in turn the textural mesoporosity, but also the polymerization extent of framework pore wall which would determine the framework mesopore properties. Both the lower aging temperature and the higher drying temperature are conducible to the formation of a high-quality BMS silica xerogel. However, over the range studied, aging and drying conditions had no significant effect on the framework mesopore sizes, though the corresponding specific surface areas and pore volumes can, be varied markedly.

Influence of synthesis parameters on the formation and structure of bimodal mesopore silica in a controlled sol-gel process

In the present work, a series of synthesis parameters, including those that may affect the size of surfactant micelles and that may affect the relative rate of hydrolysis and condensation of tetraethyl orthosilicate (TEOS), were judiciously adjusted to study their direct influence on the formation and structure of our previously reported bimodal mesopore silica (designated as BMS). It is found that both the framework and textural mesopores of BMS silica can be tailored over a fairly wide size range, but on the whole the textural mesopore size is more sensitive to the change of the synthesis parameters than that of the framework mesopore size. The change of three synthesis parameters, such as increasing the amount of ethanol, decreasing the chain length of surfactant or increasing the alkali/silica molar ratio, would lead to the mesostructure of the silica obtained to transform from initial BMS into MCM-41.