Abstract
This thesis conducts a comprehensive investigation of the of the physical chemistry related to the TEOS-based porous materials prepared by so-gel approach and develops the fast qualification technology for the hydrolysis and condensation reaction of sol-gel process. The porous materials were prepared by introducing a polymer polyethylene glycol (PEG) into sol-gel after different aging times and with different drying and annealing processes. The effects of pH and addition of PEG on sol-gel derived SiO2 powders for purification of ethanol are studied. The methods and results of this work provide valuable reference for the development of other functional materials such as low k dielectric materials.
In the first part, the long-term behavior of the hydrolysis and condensation reaction of the tetraethoxysilane (TEOS) pre-solution at different pH values with and without addition of polyethyleneglycol (PEG) for various aging times was characterized by liquid 1H, 13C, and 29Si NMR spectroscopy.The experimental results demonstrate that alcohol was generated in the TEOS pre-solutions with and without addition of PEG at pH 3 and pH 9 after aging, implying the occurrence of hydrolysis and condensation. The rate of hydrolysis and condensation for the TEOS pre-solution at pH 3 was found to follow the trend of the pre-solution with PEG 2000 > pre-solution with PEG 200 > pre-solution without PEG.
However, after adding PEG, the oxygen atom of the deprotonated silanol group (siloxy) of the hydrolyzed TEOS pre-solution at pH3 acted as a reaction center. The result indicates that the oxygen atom is more susceptible to electrophilic attack, resulting in an increased reaction rate. Consequently, the rate of hydrolysis and condensation for of the TEOS pre-solution at pH 9 follows a different order: pre-solution with PEG 200 > pre-solution without PEG > presolution with PEG 2000. The slowest reaction rate of the
TEOS pre-solution when adding PEG 2000 is related to the tangled chains of PEG 2000 which sterically reduces the hydrolysis and condensation reaction. This work shows that the correlation between the pH and aging time on hydrolysis and condensation reaction of the TEOS pre-solution can be effectively monitored by liquid 1H NMR spectroscopy, supported by 13C and 29Si liquid NMR spectra. The data obtained should assist optimizing the pH, polymer type/size/concentration and the aging time in the preparation of polymer modified TEOS sols
In the second part, SiO2 powders were prepared by the sol-gel in combination with oven-drying method before and after annealing.The experimental result demonstrates the rate of hydrolysis and condensation occurs at a fast rate in TEOS with and without adding PEG at pH3 than in any other pH levels. Because free space can lead to the vaporization of H2O, the ionization of ammonia decreases (i.e., reduction the amount of hydroxide ion), which arises from the rate of hydrolysis and condensation decreases when TEOS at pH9. After attaching PEG, the oxygen atom of the deprotonated silanol group (siloxy) for of the hydrolyzed TEOS pre-solution at pH 3 acted as a reaction center. The result indicates the oxygen atom is more susceptible to electrophilic attack, resulting in an increased reaction rate. Thus, a maximum in the powder yield is reached for TEOS pre-solution with and without adding PEG at pH 3. The SiO2 powder with adding PEG of higher molecular weight presents higher adsorption capacities, pertaining to a greater amount of hydrophilic hydroxyl groups of PEG with higher molecular weight. After annealing, the surface area of SiO2 powder prepared from the TEOS pre-solutions increases as compared with powder without adding PEG and enhances the adsorption of water. A potential absorbent SiO2 powders for producing purified ethanol suitable for fuel and industrial use, can be fabricated by using sol-gel route by careful selection of pH and PEG molecular weight.
In addition, during the preparation and characterization of these materials, some interesting phenomena were observed, which are academically valuable. For instance, some samples show very narrow 1H MAS spectra and yet has high 1H-29Si CPMAS sensitivety. This phenomenon suggests us that CPMAS sensitivety may be improved by a new route, i.e., by properly preparing the sample so that CP efficiency is enhanced.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0803112-081439 |
| Date | 03 August 2012 |
| Creators | Wu, Cheng-Hsien |
| Contributors | Chin-Hsing Chou, Shangwu (Sam) Ding, Chia C. Wang, Kuo-hsun Chiu, Ming-Yuan Liao, Jyh-Tsung Lee |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0803112-081439 |
| Rights | user_define, Copyright information available at source archive |
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