Chalcogen-Bond-Driven Electrochemical Bromide Sequestration in Benzothiazole-Functionalized Covalent Organic Frameworks.

Bromide contamination in water sources is a growing health concern because it can generate carcinogenic disinfection byproducts during conventional water treatment. However, the selective removal of bromide from reverse osmosis (RO) permeate remains challenging. Herein, we report a benzothiazole-functionalized covalent organic framework (COF) designed as a chalcogen-bond donor, where σ-holes along the C─S bond axes preferentially interact with the softer, more polarizable Br- over Cl-. Two COFs, mesoporous BTzTp (∼2.45 nm) and microporous TTzTp (∼1.13 nm), were investigated to assess the role of pore accessibility while preserving identical recognition sites. The BTzTp@rGO composite exhibited a specific capacitance of 47 F g- 1 and a maximum bromide adsorption capacity of 36.7 mg-Br- g- 1at pH 4. Notably, it maintained ∼99% capacitance retention after 50 cycles, representing the highest cycling stability reported for a bromide-selective HCDI electrode, together with excellent selectivity (αBr/Cl = 10). Density functional theory calculations reveal that selectivity originates from strong chalcogen bonding, evidenced by near-linear C─S···Br- geometries (178°-179°), normalized contacts of 0.84, HOMO delocalization across the S···Br- interface, and greater charge transfer to Br- (0.222 e) than Cl- (0.154 e). This work demonstrates a viable strategy for highly selective and stable bromide removal in energy-efficient water purification systems.