Br改性Mg-MOF-74吸附分离CO2性能研究

CO2 adsorption and separation in Br-group-modified Mg-MOF-74

中文关键词: 金属有机骨架材料  巨正则蒙特卡罗  密度泛函理论  CO2吸附与分离

英文关键词: Metal-Organic Frameworks  Grand Canonical Monte Carlo  Density Functional Theory  CO2 adsorption and separation

中文摘要:

      金属有机骨架材料Mg-MOF-74因不饱和金属位的存在具有低压下较高的CO2吸附量，且具有化学表面可修饰、可调控孔径等特点。本文基于密度泛函理论和巨正则蒙特卡罗方法对Mg-MOF-74进行官能团Br改性，发现Br改性使得苯环附近产生更强的静电势梯度，增强了骨架原子和极性CO2分子间的相互作用，利于CO2在骨架孔道内的吸附。但Br的引入带来了骨架自身比表面积、孔体积的下降，不利于在高压区CO2吸附。在摩尔比CO2:N2=15:85条件下，Br改性使得骨架对混合气体中CO2分离比相比改性前提高了近64%。在含湿条件下(CO2:N2:H2O=15:84:1)，Br改性使得H2O质量吸附量大大下降，低压下的分离比得到提高。

英文摘要:

      Mg-MOF-74 has excellent CO2 adsorption capacity at lower pressure with characteristics of post-synthesis modification, tunable porosity due to the existence of unsaturated metal sites. In this work, effects of Br functional groups on CO2 adsorption in Mg-MOF-74 were explored by Density functional theory and Grand Canonical Monte Carlo simulation. The results show there exists an enhanced interaction between CO2 and frameworks because of a deeper negative electrostatic potential gradient brought by Br-group, which facilitates CO2 adsorption on adsorptive sites inside the pores. However, the modification of Br-group in Mg-MOF-74 contributes to the decrease of free volume and surface area, leading to the decline of adsorbed CO2 molecules at higher pressure. What is more, the selectivity of CO2 over N2 of Mg-MOF-74 increases by approximately 64 percent resulted from Br-group in a mixture-component gas (CO2:N2=15:85). Meanwhile, the H2O gravimetric uptake of frameworks descends significantly, and the Selectivity of CO2 over N2 rises positively at low pressure though Br-group modification in wet mixtures (CO2:N2:H2O=15:84:1).