CO₂and CH₄Adsorption Performance Of Modified Metal-organic Framework MIL-53（Cr）

Since the21st century, the energy issue has increasingly aroused people’sconcern.Among all kinds of fossil fuel consumption,biogas is a kind of renewable clean greenenergy, its main composition is methane.How to obtain high purity carbon dioxide in themethane is problem and challenge that we are faced with.MIL-53（Cr）, featured by itsenvironment-friendly and accessible partial unsaturated metal sites, is one of the mosteye-catching nano-materials among MOFs. The present researches concerning the productyield, the adsorption and desorption of carbon dioxide, methane and the hygroscopic propertyof MIL-53(Cr), which has a broad prospect.Although previous modified materials improvethe CO2adsorption, but with a disadvantage of complicated synthesis process and the loss oflarge specific surface.In this research,attempt to use ammonia modified MIL-53(Cr) in orderto improve the adsorption ability of carbon dioxide, and ensure the larger specific surfacearea.The hydrothermal synthesis of MIL-53(Cr), and then modified with ammonia vapor, andthe modified MIL-53(Cr) were characterized and adsorption properties of carbon dioxide andmethane and water vapor. In order to solve these problems, it is necessary to do the followingworks.MIL-53（Cr）crystals were synthesized by hydrothermal synthesis method, and thenmodified by ammonia vapor of different concentrations to obtain the modified materialsNH3@MIL-53（Cr）. The CO2and water vapor isotherms on the NH3@MIL-53（Cr）weredetermined by means of gravity method. Results showed that although the specific surfacearea of the modified materials NH3@MIL-53（Cr）became smaller compared to originalMIL-53(Cr), their CO2adsorption capacities on per unit surface area of adsorbent becamesignificantly higher, following the order: NH3@MIL-53(Cr)-3#> NH3@MIL-53(Cr)-2#>NH3@MIL-53(Cr)-1#. In addition, Isotherms of water vapor on the modified samplesNH3@MIL-53(Cr) were lower than that on the MIL-53(Cr), suggesting the hydrophobicity ofthe modified samples had been significantly improved. The CO2adsorption capacity of theNH3@MIL-53(Cr)-2#modified by using ammonia vapor of1mol/L was the highest amongthe modified samples. Besides study of the modification of NH3@MIL-53(Cr) of water vapor adsorptionquantity, due to the specific surface area of the modified materials decline, so the modifiedNH3@MIL-53(Cr) materials for the water vapor adsorption capacity decreased obviously,suggesting that NH3@MIL-53(Cr) the surface of the material of water vapor adsorptionforce weakened obviously.Finally, More interestingly, the CO2adsorption performance of the modified sampleNH3@MIL-53(Cr)-2#was significantly improved, while its CH4adsorption performance wasweakened, which would be helpful to enhance its selectivity for CO2/CH4adsorption.