Novel eco-friendly nitrogen-rich-fluorinated porous polymers for high-performance removal of dyes from wastewater

Synthetic dyes discharged from industrial processes pose a persistent and severe threat to aquatic ecosystems, necessitating the development of advanced adsorbent materials capable of simultaneous and broad-spectrum dye removal. Herein, we report the synthesis of two novel nitrogen-rich, fluorinated porous organic polymers (POPs) – F-POP1 and F-POP2 – via a simple Schiff-base condensation strategy for the simultaneous and efficient removal of dyes with opposite charges, namely methyl orange (MO) and methylene blue (MB). The structural integrity and porosity of the POPs were confirmed by FT-IR, PXRD, TGA, and N₂ sorption analyses, revealing excellent thermal stability up to 360 °C, along with high surface areas of 691 and 1009 m²·g⁻¹ for F-POP1 and F-POP2, respectively. Systematic adsorption studies conducted under varying pH conditions and dye concentrations demonstrated significant performance toward both dyes, with maximum adsorption capacities reaching 319 and 427 mg·g⁻¹ for MO and 257 and 313 mg·g⁻¹ for MB on F-POP1 and F-POP2, respectively. Rapid adsorption kinetics were observed, with equilibrium reached within 6 h, achieving removal efficiencies of 48% and 75% for MO and 91% and 98% for MB using F-POP1 and F-POP2, respectively. Notably, despite the conventional tendency of fluorinated adsorbents to preferentially bind cationic dyes, both F-POPs in this work exhibited even higher affinity toward the anionic MO, attributed to the π-acidic framework induced by triazine and –CF₃ units that promotes strong donor–acceptor π–π interactions with the electron-rich aromatic structure of MO. Kinetic modeling followed a pseudo-second order rate equation, while equilibrium analysis using Freundlich, Dubinin–Radushkevich, and Temkin isotherms confirmed that dye uptake is governed predominantly by physisorption through weak noncovalent interactions, enabling efficient regeneration. Accordingly, the polymers exhibited excellent reusability over multiple adsorption-desorption cycles. Collectively, these findings demonstrate that fluorinated porous organic polymers can be chemically engineered to offer a versatile, reusable, and industrially relevant platform for the collective removal of both anionic and cationic dyes from wastewater.