Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, 210096, China.
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, 210096, China.
Chemosphere. 2021 Mar;267:129184. doi: 10.1016/j.chemosphere.2020.129184. Epub 2020 Dec 3.
In the process of municipal solid waste (MSW) pyrolysis, kaolinite possesses an outstanding trapping effect on semi-volatile metal vapors (Pb, Cd) through physical and chemical adsorption. In this paper, the microscopic mechanism of PbCl and CdCl adsorption on the surface of Al rings and Si rings of kaolinite was investigated by combining Monte Carlo method with density functional theory (DFT). The calculations indicate that the continuously enriched pore structure in the process of dehydroxylation indirectly influences the adsorption of PbCl/CdCl by kaolinite. Under the non-bond interaction and electron transfer induction, PbCl molecules are more conveniently adsorbed on the Al-(001) surface than CdCl, while the adsorption sites of CdCl molecules are more widely distributed on the Si-(001) surface. Moreover, the transform in the Al-coordination and the exposed active oxygen atoms significantly affect the adsorption activity of kaolinite (the capability to gain and lose electrons). Considering the energy barrier and electrophilic nucleophilic sensitivity, it is more feasible for PbCl/CdCl to be adsorbed near IV/V-coordinated Al and active O under Van der Waals action. Subsequently, IV/V-coordinated Al will act as an electron acceptor, and the active oxygen atoms after dehydrogenation will serve as an electron donor. Under the induction of the energy difference of frontier orbitals, the electrons transfer will encourage the formation of more stable adsorption states. The results shed new light on strengthening the adsorption activity of kaolinite to PbCl/CdCl in the process of MSW pyrolysis.
在城市固体废物（MSW）热解过程中，高岭石通过物理和化学吸附对半挥发性金属蒸气（Pb、Cd）具有出色的捕集效果。本文通过蒙特卡罗方法与密度泛函理论（DFT）相结合，研究了 PbCl 和 CdCl 在高岭石的 Al 环和 Si 环表面吸附的微观机制。计算表明，脱羟过程中不断富集的孔结构间接影响了高岭石对 PbCl/CdCl 的吸附。在非键相互作用和电子转移诱导下，PbCl 分子比 CdCl 更容易吸附在 Al-(001)表面上，而 CdCl 分子的吸附位置在 Si-(001)表面上分布更广。此外，Al 配位的转变和暴露的活性氧原子显著影响高岭石的吸附活性（获得和失去电子的能力）。考虑到能量势垒和亲电亲核敏感性，在范德华力作用下，PbCl/CdCl 更易于吸附在 IV/V 配位的 Al 和活性 O 附近。随后，IV/V 配位的 Al 将充当电子受体，脱氢后的活性氧原子将充当电子供体。在前缘轨道能量差的诱导下，电子转移将促进形成更稳定的吸附态。研究结果为强化 MSW 热解过程中高岭石对 PbCl/CdCl 的吸附活性提供了新的思路。
