甲苯分子在铝基金属-有机骨架材料上的吸附特性

Adsorption profiles of toluene molecules on Al-based metal organic framework

应用巨正则系综蒙特卡罗模拟(GCMC)方法研究了298K下甲苯在4种铝基金属-有机骨架材料(Al-MOF)上的吸附特征。通过对比模拟与实验结果,发现Dreiding力场能够较好地描述甲苯在Al-MOF上的吸附行为。由于4种Al-MOF材料均具有丰富的微孔结构,使得其甲苯吸附量(取1.5k Pa时吸附量值比较)均高于传统吸附剂的吸附量(一般小于400mg/g),分别为1375mg/g(MIL-101)、866mg/g(CYCU-3)、807mg/g(MOF-519)、504mg/g(CAU-3-BDC)。通过Snapshot图和密度分布曲线分析了甲苯在Al-MOF中的吸附位,结果表明,在低压(低负载量)时,甲苯优先吸附在骨架中的小孔道内,随压力(负载量)的增大,甲苯分子逐渐填充到大孔道。此外,甲苯与有机配体的相互作用强于与金属簇的相互作用,说明有机配体处为优先吸附位。将298K、1.5k Pa条件下甲苯吸附量与MOF的物理性质相关联,结果发现甲苯吸附量的大小与吸附剂的比表面积、孔容积成线性正相关,而与骨架密度成反比关系。

Adsorption of toluene on four aluminium based metal-organic framework（Al-MOF） was investigated by grand canonical Monte Carlo simulation（GCMC）method and laboratory adsorption tests. It was found that the adsorption of toluene on Al-MOF could be well described by the Dreiding force field. Due to the Al-MOF＇s high surface areas and abundant pore volumes,the adsorbed capacity of toluene molecules at 298 K,1.5kPa reached 1375mg/g,866mg/g,807mg/g and 504mg/g for MIL-101,CYCU-3,MOF-519 and CAU-3-BDC respectively,which were all higher than that of most traditional adsorbents（〈400mg/g）. The preferential adsorption sites of Al-MOF for toluene molecules were analyzed using snapshot and density distribution profile. Results demonstrated that toluene molecules were preferentially adsorbed into small pores when the loading amount was small. Subsequently,more molecules were adsorbed into large pores when the loading amount increased. In addition,the interaction between toluene molecules and organic ligand was stronger than that between toluene and metal cluster,which indicated that organic ligands are preferential sites. The adsorbed amount of toluene on MOF at 298 K and 1.5kPa were found to change linearly with the BET surface area,pore volume and density of frameworks,respectively.