Diketopyrrolopyrrole-based Donor-Acceptor Covalent Organic Frameworks for Iodine Capture

The recovery of radioactive iodine from nuclear waste and contaminated water sources is a critical environmental concern, which poses significant technical challenges. Herein, the study has demonstrated that tuning the electronic properties of diketopyrrolopyrrole-based donor-acceptor covalent organic frameworks (COFs) enhances iodine trapping, improves charge transport, and strengthens iodine interactions - establishing a structure-property relationship. This tuning is achieved by synthesizing COFs with the diketopyrrolopyrrole-based linker 3,6-bis(4-(1,3-dioxolan-2-yl)phenyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DKP) in combination with either the electron acceptor 4,4',4″-(1,3,5-triazine-2,4,6-triyl)trianiline (TTT-DKP) or the electron donor N₁,N₁-bis(4-aminophenyl)benzene-1,4-diamine (TAPA-DKP) linkers. These COFs, with abundant sorption sites, thermal and chemical stability, and optimized pore environments, efficiently bind iodine in the vapor and solution phases. The TAPA-DKP COF, containing electron-donating moieties, showed a high iodine uptake of 3.52 g/g, exceeding the 2.81 g/g of the electron-deficient TTT-DKP in the vapor phase, both following pseudo-second-order kinetics. Density functional theory (DFT) calculations reveal adsorption sites showing that TAPA-DKP COF binds I₂ more effectively via its electron-rich moieties, highlighting the role of electronic property modulation in iodine adsorption.