Topological tuning of Two-Dimensional polytriazine imides by halide anions for selective lead removal from wastewater

The basal spacing in the interlayer space of newly emerged two-dimensional (2D) molecular materials can be tuned to enable the intercalation of target ions. In this work, an anion intercalation strategy was used to functionalize polytriazine imides (PTIs) to achieve high heavy metal adsorption performance. The lattice structures of the PTIs were modified by intercalation of lithium ions (Li⁺) and halides. The interplanar spacing was tuned by controlling the salt matrix, temperature, and reaction time. PTI intercalated with lithium bromide exhibited an enhanced lead cation (Pb²⁺) adsorption capacity of 307.69 mg·g⁻¹ at a pH of 5.5 and 298 K compared with that of PTI intercalated with lithium chloride. The first-principle calculations revealed stronger bonding and more facile interactions between Pb²⁺ and Br^- than between Pb²⁺ and Cl^-. The anion intercalation strategy endowed PTIs with highly selective adsorption sites for Pb²⁺ (distribution coefficient K_d > 1.0 × 10⁷ mL·g⁻¹) over competing cations. A new method for controlling the interplanar spacing was proposed based on the correlation between interplanar spacing and the intercalated halide amounts. This approach suggests that interplanar spacing in the PTI network can be extended to allow other guest atoms to access the interlayer space, which is useful for efficient sorbent design for water purification.