Ultrafast Selective Enrichment of Ammonia Nitrogen from Water Using Sulfonated Covalent Organic Frameworks Bearing Single Cu Sites

Abundant and diverse functional groups of adsorbents are essential for their adsorption performances. Herein, we report a strategy to construct highly efficient ammonia nitrogen adsorbents by installing multiple ion-exchange complexation coordination-hydrogen bonding sites onto covalent organic frameworks (COFs). As a proof of concept, we prepared a COF (TpPa-SO₃H) via a modified mechanical grinding synthetic method and then obtained a sulfonated COF bearing single Cu sites (TpPa-SO₃Cu_0.5) by post-loading. Benefiting from the highly exposed active sites and ordered COF channels, TpPa-SO₃Cu_0.5 exhibited the highest adsorption kinetics among reported ammonia nitrogen adsorbents proven by the highest pseudo-second-order adsorption rate constant (k₂) of 8.97 g mg^-1 min^-1 with its maximum adsorption capacity (30.45 mg N g^-1) higher than most adsorbents (<0.001-0.994 g mg^-1 min^-1 and 0-25 mg N g^-1). Furthermore, TpPa-SO₃Cu_0.5 exhibited excellent adsorption selectivity with its selective coefficient 328 times as high as that of TpPa-SO₃H in real water (10 mg N L^-1, pH = 10). It also showed good stability and recyclability with a high ammonia recycle ratio (95.1%) after 5 adsorption-regeneration cycles. These findings pave a new way to develop unique COFs as platforms for ultrafast and selective pollutants in water and wastewater treatment.