吸附剂表面含氧官能团对苯酚吸附特性的分子动力学模拟

Molecular dynamics simulation on adsorption performances of phenol by oxygenic functional groups on adsorbent surface

煤、炭及氧化石墨烯对酚类化合物有良好的吸附性,常用作吸附剂去除含酚废水中的有害物质。上述吸附剂表面含氧官能团复杂多样,含氧官能团对酚类化合物的吸附作用尚未明确。本文采用石墨烯基底作为煤、炭等吸附剂的模型,分别采用羧基、羟基和羰基对基底进行修饰。利用分子动力学模拟方法,研究苯酚在不同含氧官能团改性吸附剂基底上的吸附过程,从范德华作用、静电相互作用、π-π相互作用、氢键作用、相互作用能等方面,探讨不同含氧官能团对吸附苯酚的影响。3种含氧官能团会对基底与苯酚之间的范德华作用、静电相互作用、π-π相互作用及氢键作用造成不同的影响。范德华作用和π-π相互作用是影响苯酚在基底吸附的主要因素;静电相互作用和氢键作用是次要的影响因素。当氢键形成位置不同时,会对苯酚的吸附产生促进或阻碍2种作用,当基底上的含氧官能团与苯酚形成氢键时会促进基底吸附苯酚,水分子与水分子之间、水分子与苯酚之间的氢键则会阻碍苯酚在溶液中的迁移。相互作用能的大小则反映了吸附过程的自发性及吸附后的稳定性,相互作用能绝对值越大表明吸附平衡后系统更加稳定,羧基有利于提高吸附剂基底吸附苯酚后的稳定性。不同含氧官能团修饰基底会使基底的亲水性有不同程度的增强,羧基最强,羟基次之,羰基几乎不增加基底的亲水性。

Coal,carbon and graphene oxide are good adsorbents for phenolic compounds.They are often used as adsorbents to remove harmful substances from phenolic wastewater.However,the adsorption performances of phenolic compounds by oxygenic functional groups,which are complex and diverse on the adsorbent surface,are not clear.In this study,graphene substrates were used as models of coal and carbon adsorbents,and carboxyl,hydroxyl and carbonyl groups were used to modify the substrates.The adsorption processes of phenol on the four different adsorbent substrates were studied by molecular dynamics simulation.The effects of different oxygenic functional groups on the adsorption of phenol were discussed from the aspects of van der Waals interaction,electrostatic interaction,π-πinteraction,hydrogen bond interaction and interaction energy.The van der Waals interaction,electrostatic interaction,π-πinteraction and hydrogen bonding between the substrates and phenol were affected by the modification of the substrates with three oxygenic functional groups.It was found that van der Waals interaction andπ-πinteraction were the main factors affecting the adsorption of phenol on the substrates,while electrostatic interaction and hydrogen bonding were the secondary factors.Two different effects,which are promoting and hindering,on the adsorption of phenol were generated depending on the position of hydrogen bonding.The hydrogen bond between phenol and oxygenic functional groups on the substrate promoted the adsorption of phenol,whereas the hydrogen bond between water molecules and water molecules or between water molecules and phenol hindered the migration of phenol in solution.The interaction energy reflected the spontaneity of the adsorption process and the stability of the adsorption system with an equilibrium state.A large absolute value of interaction energy meant a stable adsorption equilibrium system.Carboxyl group showed a strong effect in enhancing the adsorbing stability of phenol to adsorbent substrate.The hydrophilicity of the substrates can be enhanced to various degrees by modifying the substrates with different oxygenic functional groups.Specially,carboxyl group had the strongest effect followed by hydroxyl group,whereas carbonyl group hardly increased the hydrophilicity of the substrate.