Functional covalent organic framework for exceptional Fe²⁺, Co²⁺ and Ni²⁺ removal: An upcycling strategy to achieve water decontamination and reutilization as smoke suppressant and flame retardant simultaneously

A key challenge for wastewater remediation is to develop desirable adsorbents possessing abundant approachable binding sites to realize both ultra-fast capture and ultra-high absorbance for heavy metal ions. Herein, we illustrate how the three-dimensional porous covalent organic framework (COF) displays the right combination of properties, thus offering a platform for decorative chelating sites to address heavy-metal poisoning. The rational design is demonstrated by modifying polydopamine (PDA) on COF, which aims at anchoring plentiful functional groups, especially catechol groups to bind heavy metal ions. The obtained PDA-coated COF (COF@PDA) achieves rapid capture of Fe²⁺, Co²⁺ and Ni²⁺, and reaches adsorption equilibrium within 10 s. According to the Langmuir fitting, the calculated capture capacities of COF@PDA for Fe²⁺, Co²⁺ and Ni²⁺ equal 204.9, 194.2, and 207.5 mg/g, respectively. Thermodynamic studies confirmed the spontaneous and exothermic characteristic of the adsorption process. Adhering to the concept of green chemistry and sustainable development, the good catalytic performance of transition metal ions intrigues us to further investigate its flame retardant application after recovering from sewage. The “recycling” strategy of adsorbed metal ions enables the reduction of fire hazards (heat, smoke and toxic gas) of polystyrene (PS) while retaining the mechanical properties of PS composites.