Instituto de Física, Universidade de São Paulo, Cidade Universitária, São Paulo 05508-090, Brazil.
Hylleraas Centre for Quantum Molecular Sciences, University of Oslo, 0315 Oslo, Norway.
J Chem Inf Model. 2022 Dec 26;62(24):6530-6543. doi: 10.1021/acs.jcim.2c00579. Epub 2022 Sep 23.
We performed theoretical studies of CO capture in atmospheric conditions by the zeolitic imidazolate framework-8 (ZIF-8) via classical Monte Carlo (MC) simulations with Metropolis sampling and classical molecular dynamics (MD) simulations in the NVT and NPT ensembles and different thermodynamic conditions. The ZIF-8 framework was described by varying unit cell dimensions in the presence of pure gases of CO, N, O, Ar, and HO steam as well as binary mixtures of CO:N and CO:HO in s 1:1 concentration. Different chemical compositions of the framework surface was considered to provide an accurate treatment of charge and charge distribution in the nanoparticle. Hence, surface groups were represented as unsaturated zinc atom (Zn), 2-methylimidazole (mImH), and deprotonated 2-methylimidazole (mIm). Force field reparameterization of the surface sites was required to reproduce the interactions of the gas molecules with the ZIF-8 surface consistent with quantum mechanics (QM) calculations and Born-Oppenheimer molecular dynamics (BOMD). It was observed that ZIF-8 selectively captures CO due to the negligible concentrations of N, O, Ar, and HO. These molecules spontaneously migrate to the inner pores of the framework. At the surface, there is a competitive interaction between HO, CO, and N, for the positively charged ZIF-8 nanoparticle with a large binding energy advantage for water molecules (on average -62, -15, and -8 kcal/mol respectively). For the neutral ZIF-8 nanoparticle, the water molecules dominate the interactions due to the occurrence of hydrogen bond with the imidazolate groups at the surface. Simulations of binary mixtures of CO/water steam and CO/N were performed to investigate binding competition between these molecules for the framework positively charged and neutral surfaces. It was found that water molecules drastically block the interaction between CO molecules and the framework surface, decreasing CO capture in the central pore, and CO molecules fully block the interaction between N molecules and the framework. These findings show that CO capture by ZIF-8 is possible in atmospheric environments only upon dehydration of the atmospheric gas. It further shows that ZIF-8 capture of CO from the atmospheric environment is dependent on thermodynamic conditions and can be increased by decreasing temperature and/or increasing pressure.
我们通过经典蒙特卡罗（MC）模拟和 NVT 和 NPT 系综以及不同热力学条件下的经典分子动力学（MD）模拟，对沸石咪唑酯骨架-8（ZIF-8）在大气条件下捕获 CO 进行了理论研究。在存在 CO、N、O、Ar 和 HO 蒸汽以及 CO:N 和 CO:HO 的 1:1 浓度二元混合物的纯气体的情况下，通过改变单元胞尺寸来描述 ZIF-8 骨架。考虑了不同的骨架表面化学成分，以提供纳米颗粒中电荷和电荷分布的准确处理。因此，表面基团表示为不饱和锌原子（Zn）、2-甲基咪唑（mImH）和去质子化 2-甲基咪唑（mIm）。需要对表面位点进行力场重新参数化，以再现气体分子与 ZIF-8 表面的相互作用，使其与量子力学（QM）计算和 Born-Oppenheimer 分子动力学（BOMD）一致。结果表明，ZIF-8 由于 N、O、Ar 和 HO 的浓度可忽略不计，因此选择性地捕获 CO。这些分子自发迁移到骨架的内部孔隙中。在表面，HO、CO 和 N 之间存在竞争相互作用，对于带正电荷的 ZIF-8 纳米颗粒，水分子具有很大的结合能优势（平均分别为-62、-15 和-8 kcal/mol）。对于中性 ZIF-8 纳米颗粒，由于水分子与表面的咪唑基团发生氢键作用，水分子主导相互作用。还进行了 CO/水蒸汽和 CO/N 的二元混合物的模拟，以研究这些分子在带正电荷和中性骨架表面之间的结合竞争。结果发现，水分子极大地阻止了 CO 分子与骨架表面之间的相互作用，减少了 CO 在中心孔中的捕获，并且 CO 分子完全阻止了 N 分子与骨架之间的相互作用。这些发现表明，只有在大气气体脱水的情况下，ZIF-8 才能在大气环境中捕获 CO。进一步表明，ZIF-8 从大气环境中捕获 CO 取决于热力学条件，并可以通过降低温度和/或增加压力来增加。
