Sequential Pore Wall Modification in a Covalent Organic Framework for Application in Lactic Acid Adsorption

Here we describe the synthesis and postsynthetic modification of the stable β-ketoenamine TpBD(NH2)2 covalent organic framework (COF), having primary amine groups integrated into the pore walls. For this purpose we initially synthesized the nitro version of this COF, TpBD(NO2)2. Afterward, TpBD(NO2)2 was reduced to afford the desired framework having primary amine functionality. We demonstrate the accessibility of the primary amine groups and the robustness of the framework by a second modification step, the aminolysis of acetic anhydride, to obtain the corresponding amide form TpBD(NHCOCH3)2. Taking advantage of the high stability of these frameworks under acidic conditions, we study the liquid-phase adsorption of lactic acid, revealing the strong impact of a pore wall modification on the adsorption performance.