Engineered Removal of Trace NH₃ by Porous Organic Polymers Modified via Sequential Post-Sulfonation and Post-Alkylation

Although NH₃ is damaging to human health and the environment, a smart synthetic route toward adsorbents with controllable adsorption and desorption properties at ultralow concentrations remains unexplored. Herein, double postsynthetically modified porous organic polymers, obtained via post-sulfonation and post-alkylation, are reported. The sulfonated adsorbent, 1S, exhibits a record-high NH₃ capacity (4.03 mmol g⁻¹) at ≈500 ppm. Notably, the polymer can capture NH₃ even at a ppb concentration level. Hydrophobization of the sulfonated materials with alkyl chains affords cost-effective and scalable adsorbents (1SC_x and 1ESC_x), which possess a high contact angle (≈120°) with water, thus resulting in rapid desorption kinetics and exceptional recyclability under dry and humid conditions at room temperature. This is the first demonstration of this design strategy for the control of the desorption of NH₃ among porous adsorbents.