Uniform phosphazene containing porous organic polymer microspheres for highly efficient and selective silver recovery

The efficient extraction of silver ions (Ag⁺) from Ag⁺-contaminated wastewater is crucial for resource recovery and environmental protection. However, the synthesis of adsorbents with high adsorption capacity and superior selectivity for Ag⁺ is a significant challenge. Herein, a series of phosphazene-based porous organic polymers (POPs) microspheres with exceptional selectivity and adsorption capacity for Ag⁺ were rationally designed using phosphazene and aromatic amines. Notably, variations in the types of precursors induced the formation of a microsphere-like morphology with precisely controlled surface smoothness. Considering the advantages of abundant heteroatom active sites, surface charge properties and microsphere-like morphology, the synthesised networks exhibited an exceptional Ag⁺ adsorption capacity of 818.3 mg/g in aqueous solution at 45 °C, showcasing remarkable selectivity (selectivity coefficient (K_α) 3.39 × 10⁵) and an ultrafast adsorption rate, adsorbing Ag⁺ in just 5 min. These superior adsorption characteristics surpassed those of most reported POPs. Theoretical simulations further revealed that key structural motifs, particularly phosphazene units, played a critical role in enhancing Ag⁺ adsorption. This study proposes a promising strategy for the efficient recovery of Ag from wastewater using high-performance porous adsorbents.