Effect of Pyridinium Ionic Covalent Organic Frameworks on the Adsorption of Eriochrome Black T Molecules

The essence of adsorption is the interaction between adsorbate molecules and material framework. Therefore, the adsorption effect of the material is governed by to its structure. Reasonable material design requires not only the precise control of its pore structure and pore size, but also the careful tunning of the pore microenvironment of the framework. In order to explore the effect of the framework charge caused by the protonated pyridine group on the removal of Eriochrome Black T (EBT) dye from wastewater, a pair of isostructural covalent organic framework materials, TpTtp (containing pyridine group) and TpTta (without pyridine group), are used in control experiments. After being immersed in hydrochloric acid solution, TpTtp exhibits much higher removal rates for EBT (98% and 59% for TpTtp and TpTta, respectively, at an initial concentration of 150 mg / L). We attribute this to the Coulomb force between the positive ionic framework of TpTtp and the anionic EBT molecules. Adsorption experiments of Methyl Orange solutions, and anionic-cationic mixed dye solutions (EBTRhodamine B) further support our hypothesis, indicating that protonated pyridine groups can endow the porous materials with higher adsorption affinity to negatively charged dye molecules.