The Preparation of Tetraarylethylene-Based Porous Polymer Nanoparticles for the Sensitive Detection of Picric Acid in Aqueous Media

Abstract

Picric acid (PA) is difficult to self-degrade in the environment and is prone to cause soil and water pollution. Therefore, achieving highly sensitive detection of PA in the aqueous phase is of great importance for social security, as well as human health. Conjugated porous polymers (CPPs) have great potential in the field of fluorescence sensing due to their good luminescence and intrinsic porosity. In this study, tetraarylethylene-based CPP named PX-TPA containing triphenylamine groups was designed and synthesized via Suzuki-miniemulsion polymerization method, combining the porosity of the CPP, good luminescence property of tetraarylethylene, and electron-rich characteristics of triphenylamine, which are beneficial for the interaction with PA and the diffusion/transport of PA analyte in the polymer to realize an efficient fluorescence sensing. Due to the miniemulsion polymerization, the nanoparticle morphology of PX-TPA was obtained with a particle size of 75 nm, which suggests good dispersion in the aqueous phase. PX-TPA nanoparticles possess a specific surface area of 49.5 m2/g and a pore size of about 5.6 nm. The sensitive and selective detection of PA based on PX-TPA nanoparticles was obtained in pure aqueous phase, with a Stern–Volmer quenching constant up to 7.67 × 106 M–1. Moreover, the anti-interference detection of PA against other nitro compounds and common ions in water was realized. Furthermore, the spike/recovery test was used for PA detection in different water samples, and the spiked recoveries were obtained in the range of 95.80–108.00%. The t test method proves that the fluorescence sensing method with the nanoparticles as the sensing material realizes reliable PA detection at the 95% confidence level. It is concluded that the sensitive and selective detection of PA in water by PX-TPA nanoparticles is mainly attributed to the combination of excited-state photoinduced electron transfer, ground-state competitive absorption, and Förster resonance energy transfer.