CO_2在金属有机骨架材料M-MOF-74的吸附机理

Adsorption Mechanism of CO_2 on Metal-Organic Framework of M-MOF-74

金属有机骨架化合物(MOF)是一种新型的温室气体CO2吸附材料.采用密度泛函理论研究了4种金属有机骨架材料(M-MOF-74,M为Mg、Zn、Co、Ni)对CO2的吸附机理,以及N2、H2O对CO2选择性吸附的影响.结果表明,CO2主要吸附在金属位上,其吸附作用主要来自于CO2与金属位之间的范德华力和静电力.吸附后的稳定结构显示CO2分子的键角均有变化,并与金属原子形成有一定角度的M2+…OCO配合物.4种材料中Mg-MOF-74对CO2的吸附最强,吸附能为-44.38,kJ/mol,其他3种材料吸附CO2的顺序为Zn-MOF-74>Co-MOF-74≈Ni-MOF-74.N2分子在4种材料上的吸附都很弱,吸附能全部低于-20,kJ/mol,有利于CO2的选择性吸附.N2分子与金属原子形成线性M2+…NN结构.H2O分子通过氧原子与金属位之间发生静电作用,会对CO2的吸附造成一定的影响.

Metal-organic frameworks （MOFs）, as a new and effective adsorbent for CO2, have been of intense interest in recent years. Four different forms of M-MOF-74 （M = Mg, Zn, Co, Ni）were studied using density functional theory （DFT）with dispersion correction. The results suggest that CO2 is mainly adsorbed on metal cation sites through van der Waals＇ forces and electrostatic forces. After optimization, the bond lengths and angle of CO2 are changed, and CO2 is found to form an angular M2＋……OCO complex. Mg-MOF-74 has highest CO2 binding affinity （adsorption energy, -44.38 kJ/mol）. The stability of CO2 adsorption is in the order of Mg-MOF-74〉Zn-MOF- 74〉Co-MOF-74≈Ni-MOF-74. M-MOF-74 （M = Mg, Zn, Co and Ni）has low N2 affinity （below -20 kJ/mol） , which is favorable for the separation of CO2, and N2 is found to form linear M^2＋...NN complex. The interaction between oxygen of H2O and metal cation sites makes H2O affinity have higher adsorption strength than CO2 affinity, which causes negative effect on the adsorption of CO2.