Coordination-driven flexible Cu-doped covalent organic frameworks for efficient BPA capture: Synergistic adsorption mechanisms and recyclability in aquatic environments

In this study, two Cu-doped covalent organic frameworks (Cu@COFs, namely Cu@TpBD and Cu@TpMDA) were successfully synthesized via the solvothermal method to address the challenge of bisphenol A (BPA) removal in aqueous systems. The adsorption behaviors of both Cu@COFs conformed to the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating the monolayer chemisorption as the dominant mechanism. Notably, Cu@TpMDA exhibited a higher adsorption rate and a larger adsorption capacity for BPA compared to Cu@TpBD. This superior performance could be ascribed to the formation of Cu-O coordination bonds, which optimized the pore structure and enhanced the flexible features of Cu@TpMDA. The combination of characterization analyses, adsorption experiments, and density functional theory calculations revealed that the adsorption process was governed by a multi-synergistic adsorption mechanism, involving pore filling, hydrogen bond, π-π stacking, and metal coordination interaction. Remarkably, after five consecutive adsorption-desorption cycles, the BPA removal efficiencies remained over 97 % for Cu@TpMDA and 92 % for Cu@TpBD, confirming their excellent stability and reusability. The constructed coordination-driven flexible Cu@COFs system not only elucidates the structure-property-mechanism relationship, but also provides a theoretical framework for the targeted treatment of organic pollutants in complex aquatic environments.