Study On The Rapid Preparation And Adsorption Properties Of Functional Metal Organic Frameworks

With the rapid development of industry, the global warming, heavy metal ion pollution and dyeing waste can pose threats to our safety. The absorption method is usually used for the treatment of these pollutants and superior to other methods. Metal-Organic Frameworks （MOFs） have become emerging advanced porous materials and gained ever-increasing attention recently. MOFs are promising candidate materials owing to their extremely high specific surface areas and large pore volumes. MOFs chemical nature can be fine tuned and modified by selecting the appropriate building blocks, leading to tailored porous materials with promise for the CO₂ adsorption.Microwave-assisted or microwave-ultrasonic assisted synthesis can accelerate the crystallization of porous materials. In this thesis, MOFs were prepared by the microwave, ultrasonic, hydrothermal or combined methods, and applied in the adsorption of CO₂ gas, dyes, heavy metal ions etc.. The main contents and achievements can be summarized as follows:1. An amine functional MIL-53（A1） material was prepared through a clean, rapid,energy-efficient and conbined method of microwave with ultrasound irradiation. The pure phase NH₂-MIL-53（Al） can be formed in 25min. The dramatic acceleration in reaction rates suggests the removal of a passivation coating on the substrate particles and the resultant enhancement in mass and heat transfer. The porous MOFs exhibited a high thermal and chemical stability, and decomposed at the temperature of above 410℃ in air. The NH₂-MIL-53（Al） presents an excellent adsorption ability for CO₂,its adsorption capacities for CO₂ was up to 33.86 cm3 g-1 at 298 K at low pressure, which suggests chemisorption between CO₂ and pendan amine groups. Measurement of CO₂ adsorption cycles proves that the functionalized materials prepared possess good regenerability and stability.2. The amine functional UiO-66 material was prepared through a microwave assisted method. Although the synthesis of NH₂-UiO-66 has to be carried out at 120℃ for 24 under conventional reflux conditions, NH₂-UiO-66 could be prepared in 20 min by using such microwave-assisted method. The amine functional UiO-66 material has an large adsorption capacity for MB, which is about 125.30 mg g-1, and the adsorption model conforms to the langirmir adsorption.3. Zr-based MOFs （UiO-66） have attracted the attention of researchers and have been modified in direct synthesis using different functionalized linkers for the adsorption and separation of CO₂.A series of functionalized UiO-66（Zr） based MOFs, such as UiO-66, UiO-66-NH₂, UiO-66-2,5-（OH）, UiO-66-NDC, UiO-66-BPDC, were successfully synthesized. The crystal structures of these functionalized UiO-66（Zr） were similar. The amine functionalized groups play an important role in the interactions between the framework and CO₂ gas.The adsorption capacity of UiO-66-NH₂ for CO₂ was up to 3.35mmol g-1 and the heat of isothermal adsorption was 26.90kJ/mol, respectively. The adsorption of products for CO₂ can be cycled 5 times, suggesting that the preapared series of modified UiO-66（Zr） MOFs can be used for the CO₂ gas adsorption.4. Magnetic Fe₃O₄ particles exhibit high chemical stability and can be considered as the inert in most chemical transformations. The magnetic separation of nanoparticles is economical and promising for industrial applications. Owing to the convenience of retrieval of adsorbents from sample matrix,magnctization of MOFs for the applications in sample preparation has sparked great excitement.Combination of NH₂-UiO-66 with Fe₃O₄ nanoparticles allows for facile withdrawal of the porous materials by magnetic decantation. The as-synthesized materials combine the favorable attributes of both magnetic characteristics of Fe₃O₄ nanoparticles and high porosity of metal organic framework,making them excellent candidates as adsorbents. Their potential applications were used to adsorb heavy metal Hg2+ ions from environment. The results show that the magnetic NH₂-UiO-66 exhibited superior adsorption capacity for the adsorption of Hg2+. The magnetic NH₂-UiO-66 also presents well adsorption ability after five cycles of use.5. Metal-organic frameworks material are promising nanomaterials with unprecedented capacity to store small molecules. Titanium （Ⅳ） cooperated with NH₂-UiO-66 were prepared via post synthesis modification approach and their structures and properties were characterized by X-ray diffraction,Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption isotherms, and scanning electron microscopy. The resultant titanium cooperated with NH₂-UiO-66 show excellent performance for CO₂ adsorption via the formation of oxo-bridged hetero-Zr-Ti clusters. This result clearly demonstrates that the smaller Ti （IV） ions exchanged with the Zr ions of NH₂-UiO-66 may decrease the pore sizes within the framework to be closer to the ideal pore sizes for CO₂ adsorption.