磁性生物炭吸附水中甲基橙的作用机制——基于密度泛函理论与实验研究

Adsorption mechanism of methyl orange by using the magnetic biochar-Based on density functional theory and batch adsorption experiment study

以磁性生物炭(Fe_(3)O_(4)@C-NH_(2))为吸附剂,甲基橙(MO)为目标污染物,考察了浓度、温度和pH对吸附性能的影响,通过光谱学与密度泛函理论研究MO的去除机制.结果表明,吸附反应符合准二级动力学及Freundlich模型,是自发吸热且熵增的过程.平衡吸附量随着pH(3~10)升高而降低.光谱学分析结果表明,吸附作用力包括氢键、π-π堆积、π-π电子供体-受体(EDA)和静电力.静电势分布与前线轨道理论分析可知,羧基结构与MO分子间的结合能(E_(ads))与能隙(E_(gap))分别为-139.08kJ/mol,3.07eV,吸附能力高于羟基结构(E_(ads)=-94.47kJ/mol,E_(gap)=3.16eV)、氨基结构(E_(ads)=-76.10kJ/mol,E_(gap)=3.17eV)和芳香环结构(E_(ads)=-41.99kJ/mol,E_(gap)=3.18eV).基于赫什菲尔德划分的独立梯度模型-AIM拓扑分析图(IGMH-AIM)结果表明,吸附过程存在疏水作用,且氢键和π-πEDA为主要作用力.

Magnetic biochar(Fe3O4@C-NH2)was used as the adsorbent for removal of Methyl Orange(MO)in this study.The effects of concentration,temperature and pH on the adsorption performance were investigated,and then the Spectroscopic analysis and density functional theory were used to reveal the adsorption mechanism.The results demonstrated that the adsorption kinetics followed the pseudo-second-order model and the Freundlich model,and the process owned the characteristics of spontaneity,endothermic and entropy increasing.The equilibrium adsorption capacity decreased with the increment of pH(3~10).Spectroscopic analysis showed that the adsorption forces contain the hydrogen bonding,π-πbond accumulation,π-πelectron donor-acceptor(EDA)and electrostatic interaction.According to the analysis of electrostatic potential and frontier orbit,the binding energy and energy gap of carboxyl group were E_(ads)=-139.08kJ/mol,E_(gap)=3.07eV respectively,which were higher than those of hydroxyl group(E_(ads)=-94.47kJ/mol,E_(gap)=3.16eV),amino group(E_(ads)=-76.10kJ/mol,E_(gap)=3.17eV)and aromatic ring(E_(ads)=-41.99kJ/mol,E_(gap)=3.18eV).It was found that the hydrophobic action existed in the adsorption process;besides,the hydrogen bond andπ-πEDA were the main forces in the process based on the results integrating the independent gradient model and Hirshfeld partition and Atoms in molecules(IGMH-AIM).