Nitrogen-rich covalent phosphazene-based framework for efficient removal of lead(ii) ions

Abstract

Covalent organic frameworks (COFs), as a new type of porous crystalline material, are suitable for selective adsorption and separation of various heavy metal ions due to their stable framework structure, abundant surface functional groups, adjustable pore structure and large adsorption capacity. Herein, a nitrogen-rich phosphazene-based covalent organic framework was synthesized for efficient Pb²⁺ removal from aqueous solution. Adsorption equilibrium of the adsorbent could be achieved within 30 min, and the as-synthesized N-CPF exhibits an exceedingly high Pb²⁺ uptake capacity of 816 mg g⁻¹, surpassing those of most previously reported materials. The kinetics and adsorption isotherms were better fitted by the pseudo-second-order model and the Langmuir model, respectively. Furthermore, N-CPF exhibited high adsorption selectivity for Pb²⁺ compared to other heavy metals.