Two-Dimensional Triazine\nPolymers as Recyclable Fluorescent\nSensors to Detect and Remove Sub-nanomolar Hg(II) From Water

In this work, full\ntriazine two-dimensional frameworks (2DC<sub>3</sub>N<sub>3</sub>)\nwere synthesized and used to detect metal ions\nin aqueous solutions. 2DC<sub>3</sub>N<sub>3</sub> showed excellent\nperformance to sense Hg(II) with high selectivity (>96%) and was\ndesigned\nas a recyclable sensor for Hg(II) detection. 2DC<sub>3</sub>N<sub>3</sub> was synthesized using catalyst-free [2+2+2] cyclotrimerization\nof sodium cyanide and cyanuric chloride at ambient conditions. The\nas-prepared 2DC<sub>3</sub>N<sub>3</sub> sheets with several hundred\nmicrometers lateral size exhibited strong excitation-dependent fluorescence\nwith 63% quantum yield and maximum emission at 428 nm. The emission\nof 2DC<sub>3</sub>N<sub>3</sub> decreased with 14.74 × 10<sup>3</sup> L·mol<sup>–1</sup> quenching constant (<i>K</i><sub>SV</sub>) upon interaction with Hg<sup>2+</sup> ions.\nThis effect was used as a strong signal to detect Hg(II) with a 0.98\nnM detection limit. The high Hg<sup>2+</sup> removal capacity of 2DC<sub>3</sub>N<sub>3</sub> was attributed to cooperative interactions of\nnitrogen atoms of 2DC<sub>3</sub>N<sub>3</sub> pores and Hg<sup>2+</sup>, as suggested by computational studies. Taking advantage of the\nstraightforward synthesis of 2DC<sub>3</sub>N<sub>3</sub> and its\nselectivity, it can be used as an efficient platform for monitoring\nHg<sup>2+</sup> in waste and drinking water.