Large-size Porous Spherical COF-320 Prepared Via Pickering Emulsion Polymerization For Dispersion Solid-phase Extraction Of Bisphenol F

Covalent organic frameworks（COFs）are a type of porous crystal polymers with several advantages such as pre-designable pore structure,ultra-large specific surface area,strong chemical stability,easy functionalization and so on.Moreover,when used as adsorbents,COFs show high adsorption capacity for targets,so they have attracted much attentions.However,at present,most of COFs are synthesized by hydrothermal methods in one step,resulting in the difficult controlling of their morphologies.A few small-size spherical COFs have been reported in literature,but the synthesis of large-size spherical COFs is still a great challenge.In addition,bisphenol F（BPF）is a typical environmental pollutant.Due to its low concentration and complexity of environmental samples,a suitable sample pretreatment is necessary prior to analysis.Solid-phase extraction（SPE）is the mostly-used sample pretreatment method.However,most of the present adsorbents of BPF own unsatisfactory binding capacity.Therefore,It is urgent to explore new adsorbents with high adsorption capacity for pretreatment of BPF-contained samples.In view of these issues,based on a Pickering emulsion（PE）polymerization,a synthesis method for large-size porous spherical COFs（COF-320 as an example）was proposed in this dissertation,then the as-prepared large-size spherical COF-320 was applied to the dispersed solid-phase extraction（d-SPE）of BPF in water samples and orange juice utilizing its high adsorption capacity for BPF,and consequently a sensitive analysis strategy was developed for BPF.The specific research contents are listed as follows:In the first part,tetrakis（4-aminophenyl）methane and biphenyldicarboxaldehyde were used as monomers,nano-Si O₂as the stabilizer,N,N-dimethylformamide as the polar solvent and dimethicone oil as the non-polar solvent,the polymer microspheres were prepared via a PE polymerization,in which the particle size of polymer microspheres could be controlled by adjusting the stirring speed during emulsification.After that,sodium hydroxide solution was used to dissolve nano-Si O₂particles incorporated in the polymer microspheres.Finally,after the alkali-soluble polymer microspheres were dispersed in 1.4-dioxane using acetic acid as the catalyst,the porous spherical COF-320 could be obtained through a solvothermal conversion strategy with uniform and controllable sizes.The as-synthesized spherical COF-320 was characterized by infrared spectroscopy,scanning electron microscopy,powder X-ray diffraction,nitrogen sorption test and so on.The experimental results showed that the porous spherical COF-320 prepared by PE polymerization has the advantages of full spherical morphology,controllable and uniform particle size,morphology,good crystal structure,good stability and large specific surface area.The specific surface areas of porous spherical COF-320 with particle sizes of 15±5,35±5 and 55±10μm are 381.3,315.1 and 269.1 m²/g,respectively.Therefore,in this part,a two-step method containing‘PE polymerization+solvothermal conversion’was proposed to open a new viable way for the size-controllable synthesis of large-size spherical COFs.In the second part,using the above-synthesized porous spherical COF-320（15±5μm）as adsorbent,its thermodynamic adsorption,kinetic adsorption and d-SPE properties for BPF in aqueous solution were investigated,and then a new d-SPE-HPLC-UV method for the highly sensitive detection of BPF was established by combining high performance liquid chromatography（HPLC）,and finally the reusability of porous spherical COF-320 was also studied.The experimental results showed that the thermodynamic adsorption of BPF by porous spherical COF-320 fits fine to the Langmuir adsorption model.Its maximum adsorption capacity was 333.33 mg/g,much higher than that of the unconverted polymer microspheres for BPF（204.08 mg/g）.Its adsorption kinetics was well in line with the pseudo–second–order adsorption kinetic model.Moreover,porous spherical COF-320 showed good d-SPE performance for BPF with extraction efficiencies of 97.16-98.45%in the concentration range of 0.010-0.050μg/m L,and the enrichment factor was 80 folds.The developed d-SPE-HPLC-UV analytical method had a wide linear range for BPF（0.3-100ng/m L,R²=0.999）,and has a low detection limit（LOD,S/D=3）and detection amount（LOQ,S/D=10）of 0.1 and 0.3 ng/m L,respectively.The new method was successfully applied to the detection of BPF in tap water,lake water and orange juice.The recoveries of the spiked BPF were 96.0-98.6%（RSD=1.1-5.1%）,96.6-102.2%（RSD=2.0-3.8%）and 95.7-97.4%（RSD=1.4-4.4%）respectively,showing its good accuracy and precision.In addition,porous spherical COF-320 had good reusability.Therefore,in this part,a new d-SPE method for BPF in complicated samples was developed using large-size porous spherical COF-320 as adsorbent,and consequently a new analytical approach was explored for highly sensitive detection of trace BPF in water samples and beverages.