| Fossil fuels are considered as one of the most important energy sources in modern industrial society. However, the burning of fossil fuels releases huge amounts of CO2 and other greenhouse gases, leading to serious damages to the earth's ecological balance and human activity. Currently, the adsorption-based separation is considered to be one of the most effective technologies for CO2 capture and thus relevant technologies have attracted great attentions worldwide.Porous aromatic frameworks (PAFs) exhibits many interesting properties, such as permanent microporosity, ultrahigh surface area, controllable pore volume and pore size, and exceptional physicochemical stability. These excellent properties make it a good candidate for potential application in the adsorption-based and separation. In this thesis, PAF-1 was used as the precursor to prepare carbonized PAF-1 derivatives. This thesis mainly consists of three parts as follows:1. First, tetrakis (4-bromophenyl) methane was synthesized according to the reported recipe and it was then used as the monomer for the polymerization via Yamamoto-type Ullmann cross-coupling reaction catalyzed by metallic Ni to obtain PAF-1 possessing a diamond topology. Afterwards, KOH was used as the active agent to carbonize PAF-1 at high temperatures, and the effects of temperature on the structures of the carbonized PAF-1 derivatives were thereof investigated. The obtained samples were further characterized by XRD, SEM, TGA, and N2 adsorption/desorption techniques. The results show that PAF-1 possesses a high BET surface area (3921m2/g) and narrow pore distribution (?1.4nm). For the carbonized PAF-1 derivatives, the BET surface areas become smaller and their pores are also narrowed from the pore-size distribution plots,on which there are two types of pores available, one is centered at 0.5-0.8 nm while another is at 1.2nm. Within the temperature range investigated, the surface area, total pore volume, and micropore volume of the carbonized PAF-1 derivative increase with increasing the carbonized temperature, and 800? is considered as the best carbonized temperature for PAF-1.2. The carbonized sample, the so-called K-PAF-1-800 was used as the adsorbent for adsorption experiments. The single-component adsorption isotherms of CO2, CH4, and N2 on K-PAF-1-800 were measured at 25?,37?, and 50? using a static volumetric method. Then the Toth model was used to fit the measured isotherm data. The results indicate that the Toth model is able to appropriately describe the adsorption isotherms. Furthermore, the isosteric heat of adsorption as a function of loading was derived using the Clausius-Clapeyron equation and other adsorption thermodynamic properties were calculated. It is found that the isosteric heat of adsorption for all the adsorbates on K-PAF-1-800 first increases with loading and then decreases. This could be due to the fact that the adsorbent possesses two different types of pores. The adsorbate molecules first fill into the smaller pores, where the interactions between adsorbates would be enhanced when the loading is increased, resulting in the increase of the isosteric heat of adsorption as a function of loading. On the other hand, after the smaller pores are saturated, the adsorbate molecules are forced to fill into the larger pores, where the interactions between adsorbate and adsorbent become weak, leading to the decrease of the isosteric heat of adsorption as a function of loading.3. The breakthrough-column technique was used to investigate the separation performance of CO2/CH4 and CO2/N2 mixtures on K-PAF-1-800, and the obtained results indicate that K-PAF-1-800 can be used as adsorbent to separate these two mixtures. Finally, the ideal adsorbed solution theory (IAST) was used to predict the separation performance of these two mixtures on K-PAF-1-800, showing that the IAST predictions are in agreement with the results derived from the breakthroughs. |
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