Preparation Of UCNPs@COFs Fluorescent Probe For Highly Sensitive Detection Of PFOS

Perfluorooctane sulfonate(PFOS)is well-known as a typical persistent organic pollutants(POPs)due to its bioaccumulation,high toxicity and difficulty degradation,and a widespread contaminant in various environmental matrices including water,air,wildlife and humans.Toxicological studies have verified that the presence of PFOS even in trace amounts might induce serious functional damages to the human liver and kidneys and adverse effects on the fatty acid metabolism,the regenerative system,and hormones secretion system.It is of great theoretical and practical significance to develop a simple and rapid method for sensing ultra-trace PFOS.In this paper,based on covalent organic frameworks(COFs)with periodic pore structure,large surface area,easy to be functionalized and the rare earth upconversion nanoparticles(UCNPs)as a fluorescent probe with the advantage of strong anti-interference ability,we developed a rapid and highly sensitive PFOS fluorescence sensing method for COFs functionalized UCNPs sensitized by surfactant.The upconversion nanoparticles were synthesized by solvent-thermal method firstly,and COFs-functionalized UCNPs(UCNPs@COFs)were obtained by in situ formation COFs using 1,3,5-triformylbenzene and 1,4-phenylenediamine as monomers on the surface of amine groups-functionalized UCNPs by solvent-thermal method.UCNPs@COFs is an ideal core-shell structure with fluffy porous morphology on its spherical,which were analyzed by transmission electron microscope,scanning electron microscope,fourier transform infrared spectroscopy,powder X-ray diffraction and thermogravimetric analysis.The results even show that UCNPs@COFs has good stability and fluorescence properties.COF’s layer on the surface of UCNPs not only provides recognition sites for PFOS but also improves the fluorescence quantum yields from 2.15%to 5.12%.Trace PFOS can quench the fluorescence emission of UCNPs@COFs at 550 nm due to the high electronegativity of PFOS.After optimizing the solvent,the concentration of UCNPs@COFs and the reaction time,the fluorescence quenching response can be significantly strengthened in the presence of a surfactant,which causes more sensitivity.The fluorescence quenching degrees(F0-F)of the system are linear with the concentration of PFOS in the range of 1.8×10-13 to 1.8×10-8 mol/L with the limit of detection down to 1.5×10-13 mol/L(signal-to-noise ratio=3).Compared with the other six structural analogs of PFOS,UCNPs@COFs can selectively detect PFOS.This method was used to test the tap water and food packing samples,and the recovery rates were 106%～108%and 103%～104%,respectively.The proposed approach realized a simple,fast,sensitive and selective sensing PFOS,showing potential applications in food,biological,environmental and other complex samples.