School of Resources and Safety Engineering, Central South University, Changsha, 410083, China; School of Molecular Science, University of Western Australia, Perth, 6009, Australia; School of Metallurgy and Environment, Central South University, Changsha, 410083, China.
School of Resources and Safety Engineering, Central South University, Changsha, 410083, China.
Environ Pollut. 2022 Nov 1;312:120072. doi: 10.1016/j.envpol.2022.120072. Epub 2022 Sep 2.
Elucidating the mechanisms of heavy metal (HM) adsorption on clay minerals is key to solving HM pollution in soil. In this study, the adsorption of four HM atoms (As, Cd, Cr, and Hg) on the illite(001) surface was investigated using density functional theory calculations. Different adsorption configurations were investigated and the electronic properties (i.e., adsorption energy (E) and electron transfer) were analyzed. The E values of the four HM atoms on the illite(001) surface were found to be As > Cr > Cd > Hg. The E values for the most stable adsorption configurations of As, Cr, Cd, and Hg were -1.8554, -0.7982, -0.3358, and -0.2678 eV, respectively. The As atoms show effective chemisorption at all six adsorption sites, while Cd, Cr, and Hg atoms mainly exhibited physisorption. The hollow and top (O) sites were more favorable than the top (K) sites for the adsorption of HM atoms. The Gibbs free energy results show that the illite(001) surface was energetically favorable for the adsorption of As and Cr atoms under the influence of 298 K and 1 atm. After adsorption, there was a redistribution of positions and reconfiguration of the chemical bonding of the surface atoms, with a non-negligible influence around the upper surface atoms. Bader charge analysis shows electrons were transferred from the surface to the HM atoms, and a strong correlation between the valence electron variations and the adsorption energy was observed. HM atoms had a high electronic state overlap with the surface O atoms near the Fermi energy level, indicating that the surface O atoms, though not the topmost atoms around the surface, significantly influence HM adsorption. The above results show illite(001) preferentially adsorbed As among all four investigated HM atoms, indicating that soils containing a high proportion of illite might be more prone to As pollution.
阐明重金属（HM）在粘土矿物上的吸附机制是解决土壤中 HM 污染的关键。本研究采用密度泛函理论计算研究了四种 HM 原子（As、Cd、Cr 和 Hg）在伊利石（001）表面的吸附。研究了不同的吸附构型，并分析了电子性质（即吸附能（E）和电子转移）。发现四种 HM 原子在伊利石（001）表面的 E 值为 As>Cr>Cd>Hg。As、Cr、Cd 和 Hg 最稳定吸附构型的 E 值分别为-1.8554、-0.7982、-0.3358 和-0.2678 eV。As 原子在所有六个吸附位点均表现出有效的化学吸附，而 Cd、Cr 和 Hg 原子主要表现为物理吸附。空心和顶部（O）位点比顶部（K）位点更有利于 HM 原子的吸附。吉布斯自由能结果表明，在 298 K 和 1 atm 的影响下，伊利石（001）表面有利于 As 和 Cr 原子的吸附。吸附后，表面原子的位置重新分布，化学键重新配置，上表面原子周围的影响不可忽略。Bader 电荷分析表明电子从表面转移到 HM 原子，观察到价电子变化与吸附能之间存在很强的相关性。HM 原子在费米能级附近与表面 O 原子具有很高的电子态重叠，表明表面 O 原子尽管不是表面周围的最顶层原子，但对 HM 吸附有显著影响。上述结果表明，伊利石（001）优先吸附四种研究的 HM 原子中的 As，表明含有高比例伊利石的土壤可能更容易受到 As 污染。
