Superb adsorption capacity of ferrocene-based covalent organic frameworks towards Congo red with high-pH resistance

Porous materials are excellent adsorbents for the removal of organic dyes from sewage and play a significant role in environmental restoration. Herein, two ferrocene (Fc)-based covalent organic frameworks (Fc-COFs), namely FcTF-COF and FcBD-COF, are successfully synthesized for the first time through a solvothermal method, and the obtained Fc-COFs powders are used to adsorb Congo red (CR) from water. The results show that both FcTF-COF and FcBD-COF have superb adsorption performance towards CR with ultrahigh adsorption capability of 1672.2 mg g-1 and 1983.7 mg g-1 at pH = 4.0, respectively, outperforming the majority of the reported solid porous adsorbents. The maximum adsorption of both Fc-COFs agrees with the Sips adsorption isothermal model, indicating that their adsorption was dominated by heterogeneous adsorption. The Coulombic interactions, hydrogen bonding, at-at interactions and ion-dipolar interactions should all contribute to their ultrahigh CR adsorption capability and high-pH resistance performance regardless of the pH in the range of 4-9. In addition, after five cycles, both COFs still remain their exceptional high CR adsorption capabilities. This study offers a prospective organic porous adsorbent with promising applications for organic dye removal in sewage processing. (c) 2024 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).