Construction of a Cationic Pyridinium-Based Covalent Triazine Framework for Ultra-fast and Efficient Iodine Adsorption

Effective adsorption of radioactive iodine (I2) contaminants is important for environmental protection; previous works usually focused on high adsorption capacity but often ignored the adsorption rate. Here, we successfully prepare two novel cationic covalent triazine frameworks (CCTFs) with affluent pyridine cation sites under high-temperature polymerization conditions, which have ultra-high stability, high surface area, and a large electrostatic potential gradient. The synthesized CCTFs at the adjusted reaction temperature (CTF-BPMs: CTF-BPM-400 and CTF-BPM-500) have a super-fast I2 vapor adsorption rate, and the K80% (the ratio of 80% of saturated adsorption to the corresponding adsorption time) values of CTF-BPM-400 and CTF-BPM-500 are 5.94 and 3.85 g g-1 h-1, respectively, which are larger than those of any reported porous materials. Furthermore, CTF-BPM-500 can remove 99.9% of the I2 contaminant in a high-concentration I2/hexane solution (260 mg L-1) within 0.5 min, showing amazing adsorption rate and removal efficiency. The combined experimental characterization and theoretical density functional theory calculations clearly reveal the I2 capture mechanism. The abundant electron-rich triazine units and the large electrostatic potential gradient in CTF-BPMs are more conducive to inducing electron-deficient I2 molecules to form polyiodide anions (I3- and I5-), and then strong Coulombic interactions form between the abundant pyridinium cation sites of CTF-BPMs and the polyiodide anions, which significantly improve the I2 adsorption rate and removal efficiency. In addition, the high physicochemical stability makes CTF-BPMs exhibit very excellent I2 adsorption cycle capacity, which highlights their great potential in practical applications.

Automated summary

Effective adsorption of radioactive iodine (I2) contaminants is important for environmental protection. This study focused on high adsorption rate rather than just high adsorption capacity. Two novel cationic covalent triazine frameworks (CCTFs) with abundant pyridine cation sites were successfully prepared under high-temperature polymerization conditions. These CCTFs exhibited ultra-high stability, high surface area, and a large electrostatic potential gradient. The synthesized CCTFs showed super-fast I2 vapor adsorption rates and could remove 99.9% of I2 contaminant in a high-concentration I2/hexane solution within 0.5 min.