چكيده به لاتين
In recent decades, climate change driven by increasing CO2 emissions has garnered significant research attention. Carbon dioxide capture and storage (CCS) technology, leveraging porous materials, presents a promising technique for mitigating CO2 emission with high efficiency. Among porous materials, Metal-Organic Frameworks (MOFs), characterized by exceptional surface area and robust thermal stability, emerge as highly viable candidates for CO2 adsorption processes.In this research, a zirconium-based metal organic framework (MOF-808) with an NH2-containing ligand was synthesized and improved as a new mixed-ligand-based adsorbent for CO2 adsorption. The modified adsorbent showed a higher specific surface area and pore volume compared to the pristine MOF-808 while maintaining a similar microporous morphology. Next, three influential factors in the process including pressure, temperature, and the amount of NH2 loading were studied to maximize the CO2 adsorption capacity of the resulting adsorbent. The best operating conditions were observed at the temperature of 25°C, pressure of 9 bar, and 20% for the NH2-containing ligand in the MOF structure, under which the adsorption capacity of the optimized adsorbent reached 369.11 mg/g. The best kinetic model for fitting the CO2 adsorption equilibrium data was obtained the second-order Ritchie model with an R2 value more than 0.99. Also, the results of the isotherm modelling showed that the Sips isotherm model had the highest accuracy among anothers in fitting the CO2 adsorption equilibrium data. Furthermore, the negative values of thermodynamic parameters, including ΔH°, ΔG°, and ΔS°, indicated that the CO2 adsorption mechanism is exothermic and spontaneous with a decrease in disorder in the process. Subsequently, the best weight percentage of the ligand was selected, and MOF-NH2/GO-x composites with different weight percentages of graphene oxide, namely 7.5%, 15%, 22.5%, and 30%, were synthesized, and CO2 adsorption tests were performed using these composites. To determine the structural and elemental characteristics of the obtained composites, BET, FTIR, EDS, TEM, and SEM analyses were used. Moreover, the response surface methodology approach was used to investigate the effect of several factors on the adsorbents' CO2 adsorption capacity, such as the weight percentage of graphene oxide, temperature, and pressure. Using the response surface method, perturbation plots and three-dimensional response surfaces were presented. The results showed that increasing the amount of GO to 22.6% improves the CO2 adsorption capacity of the composite while increasing this factor above the mentioned value leads to a decrease in CO2 adsorption capacity. By conducting optimization, the ideal MOF-NH2/GO composite structure with a GO weight percentage of 22.6% was obtained. Although a decreasing trend in the BET surface area of the composites from 2021.37 m²/g to 1270.60 m²/g was observed by increasing the GO quantity from 0 to 22.6%, the results showed that the CO₂ adsorption capacity of the samples increased significantly from 369.11 mg/g to 482.58 mg/g. Isotherm modeling results indicated that the CO₂ adsorption process is multilayer adsorption and the surface of the MOF-NH₂/GO composite is heterogeneous. In addition, the best fit of the experimental CO₂ adsorption data by the fractional-order kinetic model showed that the reaction order cannot be an integer and the adsorption kinetics is affected by various variables including heterogeneity and adsorbent-adsorbate interactions. Thermodynamic analysis of the process showed the dominant role of the physical adsorption mechanism and the spontaneous and exothermic nature of the process. The study of the regeneration of the optimized composite after fifteen adsorption and desorption cycles showed a high degree of stability and flexibility of the adsorbent with respect to the partial loss in CO₂ adsorption efficiency (about 5.79%).
