A nitrogen-rich pyridine–melamine porous network for integrated CO₂ capture and hexavalent chromium remediation

Multifunctional adsorbents that integrate greenhouse gas capture with hazardous metal remediation are rare because simultaneously optimizing pore architecture and reactive adsorption sites remains challenging. Herein, a nitrogen-rich pyridine-based poly-melamine porous network (Py-PMAN) was synthesized via Schiff base polycondensation for integrated CO 2 capture and Cr 6+ remediation. The as-prepared polymer combines accessible porosity (S BET of 511.76 m 2 /g) with reactive amino–pyridine sites that additionally enable oxyanion sequestration. Benefiting from its nitrogen-rich porous structure and abundant amino functionalities, Py-PMAN showed a high CO 2 uptake capacity of 153.03 mg/g at 273 K and 1 bar. Distinct from conventional high-capacity Cr 6+ adsorbents that rely predominantly on electrostatic uptake, Py-PMAN couples adsorption with reduction- immobilization within a porous polymer network. Optimum conditions for Cr 6+ uptake were determined to be pH 3 and a dosage of 0.11 g/L using response surface methodology. Adsorption equilibrium and kinetics were well fitted by the Langmuir isotherm and the pseudo-second-order models, respectively, suggesting monolayer chemisorption and a high Cr 6+ adsorption capacity of 188.68 mg/g. Thermodynamic studies revealed a spontaneous adsorption process. Py-PMAN maintained high Cr 6+ removal efficiency across five adsorption–desorption cycles, indicating excellent reusability and structural stability, while competitive ion experiments confirmed strong selectivity for Cr 6+ . FT-IR and XPS analyses revealed that Cr 6+ removal proceeds through synergistic proton-assisted electrostatic binding, reduction-coupled immobilization, and coordination to amino-rich sites, with adsorption governed by these mechanisms. This work presents a robust, multifunctional porous organic network for integrated carbon capture and hazardous-metal remediation, offering a promising strategy for coupled gas purification and wastewater treatment.