BICONTINUOUS CONCENTRIC LAMELLAR NANOSTRUCTURED PARTICLE: FORMATION MECHANISM AND CATALYTIC ACTIVITY

• Main Author: FEBRIYANTI (NIM: 30515007), ERNA
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/21977
• Institution: Institut Teknologi Bandung

Bicontinuous concentric lamellar (bcl) nanostructured silica particles, KCC-1, has a unique open three-dimensional pore structure and makes significant differences among other conventional mesoporous silica. Their distinguished morphology enhance their properties and help the development of various applications in catalysis, environmental and biomedical. Among miscellaneous morphology silica particles, KCC-1 provides excellent accessibility of active surface area. Considering the wide range applications of KCC-1 and its derivatives, a good understanding of the unprecedented morphology should be carried out. <br /> <br /> <br /> <br /> This research investigated the mechanism formation, changes of chemical properties due to post-alumination, and performance of aluminated KCC-1 (Al-KCC-1) as heterogeneous catalyst on liquid phase organic reactions, i.e. cyclic acetal and cyclic imide synthesis. These two reactions were studied due to very few report of these cyclic organic chemicals synthesis using mesoporous silica-based catalyst. The ternary diagram that shows its parameter space formation reveals that bcl morphology can be obtained over a narrow range of precursor compositions (i.e. between 0.01 < CTAB/Si < 0.65 molar ratio and between the toluene/water volume ratio 2 < toluene/water < 0.55. The formation mechanism of KCC-1 can be studied from experimental point of view as well as from the theoretical side. The experimental part was carried out by observing the morphological evolution of KCC-1 as a function of synthesis time. Whereas the theoretical part was examined by taking consideration of some thermodynamic’s reversible pathways in the phase segregation section of the silica polymer (polysiloxane). <br /> <br /> <br /> <br /> The formation mechanism of KCC-1 is proposed as the hydrolysis and condensation reaction occurred in reverse micelle, followed by phase segregation process. Spectroscopic investigation on the emulsion of KCC-1 precursor shows that confined water system is existed and may play a vital role during the formation of KCC-1. Moreover, the hydrolysis and condensation reaction of silica precursor, TEOS, were proceed rigorously as soon as all of the KCC-1 precursors are well-mixed. The images of the whole part and the cross section of KCC-1 reveal that KCC-1 can be obtained just 30 minutes after the synthesis started. The morphology grows from bicontinuous lamellar (bl) morphology, with the absence of dense part in the center of particle, to the bicontinuous concentric lamellar (bcl) morphology. <br /> <br /> <br /> The theoretical part of this study is focused on the phase segregation process of polysiloxane. This process is divided thermodynamically into several reversible processes. The alterations of the lamellar orientation (i.e. paralel or perpendicular orientation) were followed as the reduced of the free energy with respect to the stacked lamellar thickness. It was merely showed that the segregation of thin polysiloxane film favors the perpendicular orientation while the thick polysiloxane film yielding a complex lamellar structure which consists of perpendicular and parallel orientations. A lamellar polymer which is confined between two planar substrates, can experience topological transformation into a sphere. When such topological transformation takes place, perpendicular lamellar orientation will give bicontinous lamellar morphology, whereas the other transforms into bicontinuous concentric lamellar morphology. <br /> <br /> <br /> Post-alumination was carried out to alter the chemical properties of KCC-1. The products (Al-KCC-1) are able to maintain the unique bcl morphology and show higher acidity with respect to KCC-1. Al-KCC-1 samples have good performance on both reactions and they can catalyze another substance to undergo similar reaction. The most active catalyst in each reaction shows good recyclability until 6 cycles of reaction. Some interesting properties of the catalyst that might be responsible to the outstanding performance are high accessibility of active sites in the bcl morphology, hydrophobicity, the presence oxygen vacancies, and penta-coordinated aluminium. <br />