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

Abundant and diverse functional groups of adsorbentsare essentialfor their adsorption performances. Herein, we report a strategy toconstruct highly efficient ammonia nitrogen adsorbents by installingmultiple ion-exchange complexation coordination-hydrogen bonding sitesonto covalent organic frameworks (COFs). As a proof of concept, weprepared a COF (TpPa-SO3H) via a modified mechanical grindingsynthetic method and then obtained a sulfonated COF bearing singleCu sites (TpPa-SO3Cu0.5) by post-loading. Benefitingfrom the highly exposed active sites and ordered COF channels, TpPa-SO3Cu0.5 exhibited the highest adsorption kineticsamong reported ammonia nitrogen adsorbents proven by the highest pseudo-second-orderadsorption rate constant (k (2)) of 8.97g mg(-1) min(-1) with its maximumadsorption capacity (30.45 mg N g(-1)) higher thanmost adsorbents (<0.001-0.994 g mg(-1) min(-1) and 0-25 mg N g(-1)). Furthermore,TpPa-SO3Cu0.5 exhibited excellent adsorptionselectivity with its selective coefficient 328 times as high as thatof TpPa-SO3H in real water (10 mg N L-1, pH = 10). It also showed good stability and recyclability witha high ammonia recycle ratio (95.1%) after 5 adsorption-regenerationcycles. These findings pave a new way to develop unique COFs as platformsfor ultrafast and selective pollutants in water and wastewater treatment.