The concentration of CO2 in the atmosphere caused by fossil fuels, power plants, and transportation is the most significant environmental issue in the world today. Intensive efforts have been made to minimize CO2 levels to reduce global warming. Metal-organic frameworks (MOFs), crystalline porous materials, exhibit great potential to adsorb carbon dioxide. In the present study, research was conducted on the synthesis, characterization, and adsorption isotherms of MIL-101. MIL-101, one type of mesoporous MOF, can adsorb enormous amounts of CO2. The synthesis was carried out using a fluorine-free hydrothermal reaction method. The porous properties, structure, morphology, thermal stability, and chemical functionalities of MIL-101 Cr were measured by N2 adsorption/desorption isotherms, X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) analysis, respectively. The volumetric uptakes of CO2 were experimentally measured at temperatures of 298-308 K and pressure of up to 600 kPa. The experimental result was correlated with the Toth isotherm model, showing the heterogeneity of the adsorbent. The heat of adsorption of MIL-101 was determined from the measured isotherm data, indicating the strength between the adsorbent and adsorbate molecule.

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Metal-organic frameworks are believed to be one of the solutions in reducing CO2 emissions. Ligand modification, which is one of the methods in optimizing the MOF structure, provides a good opportunity for the development of functional materials with better properties. Ligand functionality in gas separation is important because it provides an insight of the influence of the material topology. MIL-101 (Cr), which is a type of MOF, is composed of metal chromium and terephthalic acid as the linker. This MOF has been extensively researched for CO2 capture applications. In this work, the functionalization of MIL-101 with 1,4-Benzenedicarboxylic acid (BDC) as the ligand was carried out by changing into 2,6-Napthalenedicarboxylic acid (NDC) ligand. The design and architecture of NDC, which has a double hydrocarbon ring, is expected to increase the pore and surface area of the MOF so that it can increase gas adsorption. The synthesis of the modified MOF was performed using solvothermal method and tested for the porous properties, morphology, structure, chemical functionalities and thermal stability by N2 adsorption / desorption data, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The results show that MIL-101 NDC has better thermal stability, as it can maintain its structure up to the temperature of 350°C. The pore diameter measurement results also show a good diameter up to 4nm. The discovery structure of MIL-101 NDC which has excellent stability provides a good prospective adsorbent in CO2 capture applications.