Morphology tuned viologen-based covalent organic frameworks: a fast and targeted approach to eliminate toxic organic pollutants from water†

Abstract

Recent efforts to detoxify contaminated water with various materials have been met with limited success, largely due to an insufficient understanding of how material properties affect sorption performance. The application of porous materials with diverse morphologies in water decontamination has been ignored due to synthetic challenges and stability. Here, we report the synthesis of two chemically stable, crystalline viologen-based covalent organic frameworks (vBPDP and vMEL) with distinct morphologies; rod-shaped [vBPDP-8(R) and vMEL-7(R)] and spherical [vBPDP-7(S) and vMEL-8(S)], achieved by core plane modulations of the monomer (planar vs. nonplanar) and solvent polarity. We employed FESEM and HRTEM imaging of vBPDP at varying time intervals for a comprehensive analysis of the mechanisms of self-assembled morphologies. Furthermore, we compared the adsorption efficiencies of rod- and sphere-shaped vCOFs for removing anionic and neutral dyes from contaminated water. Rod-shaped vBPDP-8(R) and vMEL-7(R) demonstrated superior capture efficiencies compared to spherical vBPDP-7(S) and vMEL-8(S). vBPDP-8(R) achieved the highest capture of anionic dye methyl orange (1161.78 mg g⁻¹) and neutral dye fluorescein (1237.40 mg g⁻¹). DFT analysis confirmed strong non-covalent interactions between vCOFs and dyes, which strongly support our experimental results. Furthermore, the Quantum Theory of Atoms in Molecules (QTAIM) was employed to conduct a detailed atomic-level analysis of the interactions between vCOFs and dye molecules, providing insights into the nature of intermolecular contacts. This study uniquely explores the creation mechanisms and morphology-dependent performance of self-assembled vCOFs, emphasizing their potential in water treatment and material design.