改性氧化石墨烯去除重金属离子的分子动力学模拟

Molecular Dynamics Simulations of EDTA-modified Graphene Oxide for Pb(Ⅱ) and Na(Ⅰ) Removal

通过硅烷化反应在氧化石墨烯(Graphene oxide,GO)表面嫁接螯合官能团N-(三甲氧基硅丙烷)乙二胺三酸(EDTA-Si),得到改性氧化石墨烯(GO-EDTA),采用分子动力学模拟在分子水平上研究了Pb^(2+)在GO-EDTA表面的动态吸附分布、构象及动力学性质,比较了Pb^(2+)和单价Na^+离子在氧化石墨烯上的吸附行为,模拟了GO-EDTA与Ca^(2+)相互作用,与Pb^(2+)的吸附行为进行了对比.模拟结果表明,Pb^(2+)和Na^+的吸附位点是GO-EDTA体系中的羧基,而非氧化石墨烯表面的羟基;Pb^(2+)和Na^+与羧基的吸附构象不同,前者吸附构象以摩尔比2∶1为主,即两个羧基对一个Pb^(2+)离子,而后者更多倾向于摩尔比1∶1的吸附模式,即一个羧基对一个Na^+离子;Pb^(2+)离子相对于Ca^(2+)和Na^+离子,形成的COO--Pb^(2+)离子对构象越过的能垒最低,但是破坏该离子对构象时能垒较高,表明Pb^(2+)离子在氧化石墨烯膜上表现出良好的吸附性.

The chelating groups N- （trimethoxysilylpropyl） ethylenediamine triacetic acid （EDTA-silane） were linked to graphene oxide （GO） surfaces through a silanization reaction, and this modified GO （GO-EDTA） was used to remove the heavy metal in the solution. By using molecular dynamics simulation at the molecular level, the absorption distribution, dynamic properties of Pb2＋ on the GO-EDTA surface were investigated, the different absorption behaviors of Pb2＋ and Na＋ between GO and GO-EDTA systems were compared. At the same time, the interaction between GO-EDTA and Ca2＋ was simulated, which was comparable to the adsorption behavior of Pb2＋. The simulation result shows that ： （ 1 ） the adsorption sites of Pb2＋ and Na＋ are the carboxyl groups in the GO-EDTA system, rather than the hydroxyl groups on graphene oxide surface; （2） the absorption conformations of Pb2＋ and Na＋ to carboxyl groups are different. For Pb2＋ ions, they form the 2 ： 1 type with carboxyl group, i.e. one Pb2＋ ion combines with two carboxyl groups; while for Na＋ ions, it is the 1 ： 1 type, i.e. one Na＋ ion combines with one carboxyl group; （3） comparison with Ca2＋ and Na＋ ion, the energy barrier of forming COO-Pb2＋ ion pair conformation is lowest while the energy barrier to break this conformation is higher. This result indicates that the Pb2＋ ions are adsorbed well on GO and GO-EDTA films.