State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing, 100029, P. R. China.
Quzhou Institute for Innovation in Resource Chemical Engineering, Quzhou, Zhejiang Province, 324000, P. R. China.
Chemistry. 2023 Jul 3;29(37):e202300050. doi: 10.1002/chem.202300050. Epub 2023 May 9.
Layered double hydroxides (LDHs) have shown great potential as adsorbents for the removal of heavy metals. Nevertheless, how the host-guest interactions of LDHs affect the removal mechanism remains to be less explored. Herein, CO /NO /SO /Cl intercalated MgAl-LDHs with different host-guest interactions were fabricated and their removal mechanism for Cd was investigated. The removal capacity increased in the order of MgAl-CO (127.3 mg/g)<MgAl-SO (173.3 mg/g)<MgAl-NO (305.0 mg/g)≈MgAl-Cl (312.5 mg/g). The quasi-in-situ XRD and XAS demonstrated that Cd was removed as CdCO for MgAl-CO , while for MgAl-Cl/NO /SO , Cd was removed as CdAl-LDHs by an isomorphic substitution mechanism. DFT calculations revealed that compared to the CdAl-LDHs formation the Gibbs free energy of the CdCO formation was lower, which made it easier to remove Cd as CdCO on MgAl-CO . Conversely, isomorphic substitution of MgAl-NO to obtain CdAl-LDHs was a free energy reduction process.
层状双氢氧化物（LDHs）作为一种吸附剂，在去除重金属方面显示出巨大的潜力。然而，LDHs 的主客体相互作用如何影响去除机制仍有待进一步探索。在此，制备了具有不同主客体相互作用的 CO /NO /SO /Cl 插层 MgAl-LDHs，并研究了其对 Cd 的去除机制。去除容量的顺序为 MgAl-CO（127.3mg/g）<MgAl-SO（173.3mg/g）<MgAl-NO（305.0mg/g）≈MgAl-Cl（312.5mg/g）。准原位 XRD 和 XAS 表明，MgAl-CO 中 Cd 以 CdCO 的形式被去除，而对于 MgAl-Cl/NO /SO ，Cd 则通过同晶取代机制被去除为 CdAl-LDHs。DFT 计算表明，与 CdAl-LDHs 的形成相比，CdCO 的形成吉布斯自由能更低，这使得在 MgAl-CO 上更容易以 CdCO 的形式去除 Cd。相反，MgAl-NO 的同晶取代以获得 CdAl-LDHs 是一个自由能降低的过程。
