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Synthesis and Characterization of Mesoporous Carbons and Their Adsorption Properties

Author: TuGaoMei
Tutor: ZhuWeiDong
School: Zhejiang Normal University
Course: Physical and chemical
Keywords: Mesoporous carbon organic-organic self-assembly triconstituent co-assembly resol phloroglucinol formaldehyde triblock copolymer F127 adsorption
CLC: O643.36
Type: Master's thesis
Year: 2011
Downloads: 221
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Abstract

Ordered mesoporous carbons as a kind of novel porous materials that have attracted great attention due to their unique structural feature, high specific surface area, large pore volume, well-controlled pore size, chemical inertness, and good mechanical stability, are widely used in the fields of adsorption-based separation and gas storage etc. Template methods, including soft and hard template methods, are commonly used method for the preparation of mesoporous carbons. A hard template method has several disadvantages such as time-consuming, high cost, and environmental pollution. On the other hand, a soft template method to synthesize mesoporous carbons has the following merits: a simple procedure for synthesis and an easy removal of organic templates during carbonization.The current work is focused on the synthesis of mesoporous carbons by a soft template method. The synthesized materials are characterized by N2 adsorption-desorption, low-angle XRD, SEM, TEM, and TG techniques. The main results are summarized as follows:1. Mesoporous carbons were synthesized by an organic-organic self-assembly method using phloroglucinol-formaldehyde as carbon precursor and triblock copolymer F127 as template in acidic conditions. The effects of several synthetic parameters, such as molar proportion of ethanol in a water-ethanol mixture solvent, catalyst (hydrochloric acid, HC1) concentration and dose, and reaction temperature, on the textural properties of the synthesized mesoporous carbons were systematically investigated. The results show that changing the molar proportion of ethanol in the mixture solvent can significantly affect the textural properties of the synthesized materials. However, these effects on the textural properties show different trends within different ranges of the molar proportions of ethanol in the mixture solvents. As a higher molar proportion of ethanol in the mixture solvent, the well-ordered mesoporous carbons can be synthesized. When a mixture solvent with an ethanol molar proportion of 0.3 is used, changing the catalyst concentration can affect the textural properties of the synthesized samples but the effects show different trends within different ranges of the catalyst concentrations. When pure ethanol is used as solvent, however, the dose of the catalyst does not affect the textural properties and the OMC mesoporosity can reach up to 92%. In addition, an increase in reaction temperature for the initial self-assembly process causes a decrease in the BET specific surface area, total pore volume, pore size, and mesoporosity of the synthesized samples, and this temperature effect is more pronounced when synthesized in the mixture solvent.2. Mesoporous carbons were synthesized by a triconstituent co-assembly method using resole as carbon precursor, tetraethoxysilane (TEOS) as inorganic precursor, and triblock copolymer F127 as template in acidic conditions. The effects of the type and dose of carbon precursor and acid (catalyst) concentration and dose on the textural properties of the synthesized mesoporous carbons were systematically investigated. The results show that the incorporation of silica into the polymer-silica nano-composite can effectively prevent the framework shrinkage during the carbonization procedure at high temperatures. The use of low molecular-weight phenolic resins as carbon precursors result in an increase in the BET surface area (1845 m2/g) and a mesoporosity of 100%. An increase in the dose of the acid during the self-assembly process can lead to a descrease in the BET specific surface area and total pore volume. On the other hand, an excess dose of the acid used in the reaction system can reduce the mesoporosity, but the amount of the solvent used does not affect the mesoporosity. Additionally, increasing the amount of the carbon precursor can reduce the BET specific surface area and total pore volume but does not affect the mesoporosity.3. The home-designed high-pressure adsorption apparatus was extensively adjusted and tested. This apparatus was used to investigate the adsorption and storage properties of CO2 on the developed OMC adsorbents.

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