Synthesis Of Micro/Mesoporous Composites And Their Application As CO₂ Adsorbents

As the globe-warming are prominent, greenhouse gas CO2 capture and separation causes a global concernning. At present, adsorption is the one of the most promising CO2 separation and capture strategies; the key for adsorption is to design and fabricate new efficient adsorbents. In this study, series types of micro-mesoporous composites were synthesized and used as the adsorbents for CO2 capture. The micro-mesoporous composites possessed both the high CO2 capacity originated from the microporous materials and the good gas transfer properties originated from the mesoporous materials, which greatly improved the CO2 adsorption performance.In the synthesis of the micro-mesoporous composites, the effects, such as the synthesis methods, the types of microporous zeolites and the mesoporous materials, the temperature, the templates types and amounts, the pH of the solutions, the ratios of synthesis ingredients, and the hydrothermal time were studied, respectively. Among them, there were two synthesis methods:(1) the synthesized zeolite precursors were assembly with the mesoporous templates; (2) the zeolite powders were pretreated by hydrothermal under the different pH conditions, some microporous structures transferred into mesoporous structures. Meanwhile, four types of zeolites, includingβ, ZSM-5,5 A,13X; and two types of mesoporous materials, including MCM-41 and SBA-15 were investigated to fabricate the composites. The characterized results of XRD, TEM and nitrogen adsorption-desorption showed that the products contained the micropores and mesopores simultaneously and possessed high surface area and adjustable pore structures. Based on the determinations of DLS and Zeta potentials of the synthesis solutions, the synthesis mechanisms were discussed as well.On the basis of micro-mesoporous composites, the metal ions, such as Li+, K+, Mg+ Ba2+ were further introduced into the composites by the ionic exchange method. The different impregnation methods, the types of metal ions, the types of microporous zeolites, and the pH of the solutions were investigated to optimize the impregnation conditions. A series of Zeolite-MCM-41-Mn+ composites with good performance were produced.The CO2 adsorption capacity was investigated through pure CO2 adsorption-desorption isotherms at room temperature. The influences of the different synthesis methods and conditions to the adsorption capacities and rates were studied. Compared with the pure microporous or the pure mesoporous materials, the micro-mesoporous composites had an obvious improvement on the CO2 adsorption capacity. After metal ions impregnations, the metal ions on the frameworks of micro-mesoporous composites played an important role as the chemical adsorption active sites, which enhanced the CO2 adsorption, for example, the CO2 adsorption capacity of 13X-Mg2+-MCM-41 was 3.90 mmolg-1. The studies of micro-mesoporous composites and metal ions impregnations provided a type of candidate adsorbents for the efficient CO2 capture and separation.