The Preparation of\nTetraarylethylene-Based Porous\nPolymer Nanoparticles for the Sensitive Detection of Picric Acid in\nAqueous Media

Picric acid (PA) is difficult to self-degrade in the\nenvironment\nand is prone to cause soil and water pollution. Therefore, achieving\nhighly sensitive detection of PA in the aqueous phase is of great\nimportance for social security, as well as human health. Conjugated\nporous polymers (CPPs) have great potential in the field of fluorescence\nsensing due to their good luminescence and intrinsic porosity. In\nthis study, tetraarylethylene-based CPP named PX-TPA containing triphenylamine\ngroups was designed and synthesized via Suzuki-miniemulsion polymerization\nmethod, combining the porosity of the CPP, good luminescence property\nof tetraarylethylene, and electron-rich characteristics of triphenylamine,\nwhich are beneficial for the interaction with PA and the diffusion/transport\nof PA analyte in the polymer to realize an efficient fluorescence\nsensing. Due to the miniemulsion polymerization, the nanoparticle\nmorphology of PX-TPA was obtained with a particle size of 75 nm, which\nsuggests good dispersion in the aqueous phase. PX-TPA nanoparticles\npossess a specific surface area of 49.5 m<sup>2</sup>/g and a pore\nsize of about 5.6 nm. The sensitive and selective detection of PA\nbased on PX-TPA nanoparticles was obtained in pure aqueous phase,\nwith a Stern–Volmer quenching constant up to 7.67 × 10<sup>6</sup> M<sup>–1</sup>. Moreover, the anti-interference detection\nof PA against other nitro compounds and common ions in water was realized.\nFurthermore, the spike/recovery test was used for PA detection in\ndifferent water samples, and the spiked recoveries were obtained in\nthe range of 95.80–108.00%. The <i>t</i> test method\nproves that the fluorescence sensing method with the nanoparticles\nas the sensing material realizes reliable PA detection at the 95%\nconfidence level. It is concluded that the sensitive and selective\ndetection of PA in water by PX-TPA nanoparticles is mainly attributed\nto the combination of excited-state photoinduced electron transfer,\nground-state competitive absorption, and Förster resonance\nenergy transfer.