| Metal-organic framework MIL-101is a new porous material and has attracted both academic and industrial attentions for their potential applications in gas separation and storage, drug delivery and catalysis due to its ordered porous structure, high surface area and adjustable chemical functionality. However, the yield of MIL-101synthesized by general hydrothermal method is rather low with quite high synthesis temperature. In this study, the synthetic parameters of MIL-101were systemically investigated and imidazole was employed in the process of synthesis of MIL-101to enhance the yields and decrease the synthesis temperature. Meanwhile, the obtained materials were characterized and evaluated by CO2adsorption. The following statements were the main obtained results and conclusions:(1) The influence of metal center, anion of chromium, additives, seed crystals and purification on the synthesis of MIL-101were investigated. The results showed that the anion of chromium salts affected the morphology and crystal phase of the products. SO42-could cause cloud-like morphology of MIL-101and transform MIL-101phase to MIL-88phase while extending the synthesis time. F" and Cl" were the key factor of phase-transition between MIL-101phase and MIL-53phase and could enhance the crystallinity. Due to higher solubility of terephthalic acid in the presence of alkaline additives, MIL-101synthesized using alkali additive presented good crystallinity, well-defined morphology and uniform grain size. Meanwhile, alkali additive can inhibit phase-transition and provide a phase-selective synthesis toward MIL-101. The powdered MIL-101as a crystallization seed during the synthesis of MIL-101could accelerate the crystallization, decrease the induction period, and enhanced the yield of MIL-101. Meanwhile, the morphology of MIL-101synthesized by adding seed crystals was well-defined octahedron, and the grain size of that was uniform. Moreover, the yield of MIL-101could be enhanced by extending synthesis time or increasing the synthesis temperature.(2) MIL-101was synthesized using2-methylimidazole,4-methylimidazole or2-ethyl-4-methylimidazole as additives. The yield of MIL-101was increased due to the easier deprotonation of terephthlalic acid in these imidazoles solutions. The influence of synthesis condition on the products was investigated. The results showed that MIL-101samples synthesized presented well-defined octahedral morphology and uniform distribution of particles size. The synthesis temperature was lower than180℃and the highest yield of MIL-101sample was70%. The CO2adsorption capability of MIL-101synthesized by4-methylimidazole at1.0MPa was313mg/g and the selectivity of CO2/N2was7.56.(3) MIL-101synthesized by4-nitroimidazole-asstaint route presented well-defined octahedron morphology and uniform grain size. The synthesis temperature in this route was reduced down to150℃and the yield of MIL-101was enhanced to90%. The synthesis time was reduced by adjusting the concentration distribution of reactant and the yield of MIL-101by dynamic crystallization method was higher than static crystallization method. The grain size of MIL-101synthesized by dynamic crystallization method was smaller than that of the static crystallization method. The CO2adsorption capability of MIL-101synthesized by4-nitroimidazle at1.0MPa was343mg/g and the selectivity of CO2/N2was7.06=... |
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