Phosphazene-based covalent organic framework: Advanced lead-capture material with visual indicator for efficient water purification

A nitrogen-phosphazene-based covalent organic framework (PT-COF) has been synthesized for the selective and efficient removal of lead (Pb²⁺) ions from contaminated water. Constructed through a solvothermal reaction between hexa(4-formyl-phenoxy)cyclotriphosphazene and 1,3,5-tris-(4-aminophenyl)triazine, PT-COF exhibits a remarkable adsorption capacity of 940 mg/g, outperforming many conventional adsorbents. Adsorption equilibrium is achieved within just 20 min, highlighting its rapid kinetics. The material demonstrates exceptional selectivity for Pb²⁺ ions, even in the presence of competing contaminants, making it highly effective in complex water treatment scenarios. Moreover, PT-COF features a visual colorimetric indicator, transitioning from yellow to dark brown during Pb²⁺ ion adsorption, simplifying real-time monitoring. Its reusability was confirmed through five successful regeneration cycles without significant loss of efficiency, presenting PT-COF as a sustainable, cost-effective, and practical solution for industrial water purification and the mitigation of environmental lead pollution.