Preparation of high-capacity magnetic polystyrene sulfonate sodium material based on SI-ATRP method and its adsorption property research for sulfonamide antibiotics
KeywordsPolystyrene sulfonate sodium (PSS) magnetic material Surface-initiated atom-transfer radical polymerization (SI-ATRP) Sulfonamide antibiotic Adsorption performance High performance liquid chromatography (HPLC)
Codex Alimentarius Commission
sodium styrene sulfonate
polystyrene sulfonate sodium
Sulfa drugs (SAs) are a class of synthetic anti-infective drugs with a wide antibacterial spectrum. They are also convenient to use and stable in nature. Owing to these advantages, SAs are widely used in aquaculture and animal breeding [1, 2, 3, 4]. However, bacteria easily become resistant to sulfa drugs, and sulfa drug residues can accumulate in animals after long-term use. Therefore, the United Nations Codex Alimentarius Commission (CAC) and many national regulations have limited the total amount of SAs in animal feed to 0.11 mg/kg [5, 6]. At present, sulfa drugs in China are mainly treated by simple physicochemical methods [7, 8], SBR (sequencing batch activated sludge leads to normal flora imbalance in the body ), and adsorption methods [10, 11].
Surface-initiated atom-transfer radical polymerization (SI-ATRP) is a new actively controlled polymerization technology that enables “active” polymerization. Because it controls the graft chain length [12, 13, 14], SI-ATRP grafting is a popular surface graft-modification technique for various materials. Using SI-ATRP technology, Niu et al.  obtained an aminated resin with higher adsorption capacity for Cu(II), Pb(II), Cr(VI), and As(V) than traditional resins. By the same technology, Chen et al.  prepared a chelate resin with a 4-vinylpyridine ring as the functional group. This resin readily adsorbs Cr(VI), Pb(II), and Cr(III).
The unique magnetic properties of Fe3O4 magnetic nanomaterials have been widely exploited in magnetic fluids, data storage, and pollutant treatments [17, 18]. Jin et al.  prepared monodispersed carboxylated Fe3O4 magnetic nanoparticles, and Cheng et al.  studied the adsorption performance of amino-functionalized mesoporous magnetic nanoparticles on Cu(II) in water, but not in actual samples. Therefore, the performance of their nanoparticles in real applications is unknown. To fill these gaps, we prepared magnetic materials by grafting modified Fe3O4 magnetic nanoparticles onto sodium styrene sulfonate, and testing their ability to adsorb antibiotics from food. To this end, we detected the adsorbed and remnant sulfa antibiotics in a food source (milk) treated by the magnetic material, which has not been reported in the prior literature.
In this study, the carrier/initiator was a brominated magnetic material, the monomer was sodium styrene sulfonate (NaSS), and the catalyst was cuprous bromide/2,2′-bipyridyl. A novel sodium polystyrene sulfonate magnetic material was prepared by the SI-ATRP technique. Adsorption and removal experiments of the sulfa antibiotics were performed under various conditions of the magnetic material, yielding informative results.
Materials and methods
Experiments were carried out in the following instruments: an LC-20AT high performance liquid chromatograph (Shimadzu Corporation, Japan), a JEM-2100 transmission electron microscope (JEM, Japan), a JJ-1 precision factory electric mixer (Shanghai Specimen Model Factory), a collecting thermostatic heating magnetic stirrer (Zhengzhou Changcheng Branch Industry and Trade Co., Ltd.), a KQ-3200E ultrasonic cleaner (Kunshan Ultrasonic Instrument Co., Ltd.), a BS-224S electronic balance (Sedolis Scientific Instrument Co., Ltd.), an SHZ-C type water bath constant-temperature oscillator (Shanghai Pudong Physical Optics Instrument Factory), a TU-1810 UV–visible spectrophotometer, (Beijing Pu Analysis General Instrument Co., Ltd.), a TGL-20 M high-speed desktop centrifuge (Changsha Xiangyi Centrifuge Co., Ltd.) and a Fourier transform infrared spectrometer (Shimadzu, Japan). The absorbance was measured by the TU-1810 UV–Vis spectrophotometer purchased from Beijing Pu Analysis General Instrument Co., Ltd. The supernatant after adsorption by the material was photometrically determined to determine the absorption wavelength of the sulfonamides. Then, spectral scanning was performed, and different absorbances were measured and processed by UVWin5 software to complete the experiment. The actual sample was analyzed by LC-20AT high performance liquid chromatography (Shimadzu Corporation, Japan). The instrument was equipped with DGU-20A3 degasser, 2 LC-20AT solvent transfer pumps (divided into A and B pumps), and 7725i manual feed. Sampler, CTO-20A column oven, SPD-20A UV–Vis detector and CBM-20A system controller. Diamonsil C18 column (150 mm × 4.6 mm, 5 μm), mobile phase acetonitrile–water (25:75, v/v) and filtered through a 0.45 μm filter with a flow rate of 0.8 mL/min and a detection wavelength of 270 nm and set the injection volume of 20 μL.
Reagents and materials
Sodium styrene sulfonate (NaSS), sulfamerazine free acid (SMR), sulfadimethoxine (SDM), sulfafurazole (SIZ), sulfadimidine (SM2), N,N-dimethylformamide (DMF), 3-aminopropyltriethoxysilane (MSDS), α-bromoisobutyryl bromide,hydroxylamine hydrochloride, oleic acid, tetraethyl orthosilicate (TEOS), cuprous bromide (CuBr) and 2,2′-bipyridine (Bpy) were purchased from Aladdin Reagent Co., Ltd. (Shanghai, China). Ferric chloride hexahydrate (FeCl3·6H2O), ethylenediaminetetraacetic acid (EDTA), aqueous ammonia (NH3·H2O), hydrochloric acid (HCl), acetonitrile,methylbenzene,sodium hydroxide (NaOH), absolute ethyl alcohol,tetrahydrofuran, and triethylamine were purchased from Damao Chemical Reagent Factory (Tianjin, China).
Preparation of magnetic Fe3O4/SiO2 nanocomposite particles
FeCl3·6H2O (60 mL, 0.05 mol/L) and ethanol–water (1:1 v/v) were placed in a round-bottomed flask and heated to 50 °C with magnetic stirring. At the start of stirring, 0.0511 g hydroxylamine hydrochloride was quickly added to the mixture. After 5 min of stirring, the pH was adjusted to > 9.0 by adding 25% ammonium hydroxide. Next, 1 mL oleic acid was slowly (dropwise) added to the solution while warming to 70 °C for 10 min. After stirring for a further 30 min at 70 °C, the solution was allowed to cool to room temperature. The solids were then separated by a solid magnetic field. The resulting black precipitate was washed several times with absolute ethanol and vacuum-dried at 60 °C.
Weighed Fe3O4 particles (1.00 g) were ultrasonically dispersed in 100 mL ethanol–water (4:1 v/v) for 10 min. The dispersed solution was transferred to a 250-mL three-necked bottle. After adding 2 mL 25% ammonium hydroxide and (slowly) 1 mL TEOS, the mixture was mechanically stirred until uniform, and the reaction was sealed for 24 h. After completion of the reaction, the solution was repeatedly washed with distilled water under the magnetic-field separation conditions until it became neutral and no longer cloudy.
Synthesis of Fe3O4/SiO2 grafted PSS composites
Dried Fe3O4/SiO2 (1.00 g) solid particles were weighed into a 100 mL three-necked flask. After adding 20 mL of absolute ethanol, the particles were ultrasonically dispersed for 15 min. When the dispersion was complete, 3 mL of MSDS was added and the reaction was heated in a 90 °C oil bath for 24 h After completion of the reaction, the mixture was washed successively with toluene, secondary water and absolute ethanol until neutral, and vacuum-dried at 60 °C.
The aminosilylated Fe3O4/SiO2 (0.5 g) was dispersed in 30 mL of tetrahydrofuran, and the reaction was stirred for 30 min in an ice bath. Triethylamine (1.25 mL) was then added dropwise, and the mixture was stirred at room temperature for 10 min. After dropwise of 1 mL α-bromoisobutyryl bromide, the reaction was left at room temperature for 20 h to complete the reaction. The product was washed twice with tetrahydrofuran, distilled water and acetone, and vacuum-dried at 60 °C.
Initiator-modified Fe3O4/SiO2 (0.3 g) was weighed into a 50 mL round-bottomed flask. After adding 0.0743 g Bpy, 0.0213 g CuBr, and 0.995 g sodium styrenesulfonate in 40 mLNN-dimethylformamide–water solution, the Fe3O4/SiO2 particles were ultrasonically dispersed for 15 min. Nitrogen was then deaerated for 30 min at room temperature, and the reaction was sealed at 60 °C for 20 h. After the reaction, the polymerization product was separated by a magnetic field, and the impurities in the precipitate were removed by sequential washing with saturated EDTA, distilled water and acetone (two washes in each cleaning agent). The product, polystyrene sulfonate sodium (PSS) magnetic material, was vacuum-dried at 60 °C.
Adsorption selectivity: To determine the adsorption selectivity of SMR, we prepared additional target molecules SDM, SM2, and SIZ, which are similar to SMR. Into solutions of 0.6 mmol/L acetonitrile (10 mL) and 0.1 mol/L NaOH (9:1 v/v) was weighed 0.1 g of magnetic material. The mixtures were oscillated in a water bath at constant temperature. After static adsorption for 24 h, the absorbances of the supernatants were measured in a UV–visible spectrophotometer, and the adsorption amounts of the magnetic materials were calculated by Eq. (1).
Adsorption kinetics: The adsorption kinetics were measured under the condition of pH > 7. Magnetic material was added to the same concentration of SMR solution. The mixture was continually oscillated in a constant-temperature oscillator and sampled regularly. The adsorption amounts were determined from the absorbances measured at each sampling time, and an adsorption amount–time curve was plotted to determine the adsorption rate. The experimental results were analyzed by different kinetic models and the kinetic reaction order was determined.
Adsorption thermodynamics: The adsorption thermodynamics were measured under the condition of pH > 7, a constant amount of the magnetic materials was added to different initial concentrations of SMR solution. The solutions were continually oscillated in a constant-temperature oscillator. The adsorption was balanced and sampled. The adsorption isotherm was obtained by plotting the equilibrium concentrations and the corresponding equilibrium adsorption amounts as the abscissa and ordinate, respectively. The adsorption amounts were investigated at different temperatures, and the relevant thermodynamic parameters were calculated from the results.
Adsorption properties under different pH
0.1 g of sodium polystyrene sulfonate magnetic material was placed in an aqueous solution at 25 °C, and the pH values were 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0, respectively. The initial concentration of the SMR solution was 0.6 mmol/L. Adsorption was carried out for 7.5 h under magnetic stirring. And calculate the adsorption amount of SMR.
Milk samples (5 mL) were accurately transferred into a 50 mL centrifuge tube. After adding a certain amount of the sulfa drug standard solution, 1 mL hydrochloric acid solution (1 mol/L) and 15 mL acetonitrile, the mixture was ultrasonicated for 20 min, then centrifuged at 4000 rpm for 10 min. The supernatant was collected through a filtration membrane, spin-dried, then reconstituted in 5 mL of acetonitrile. The vials were placed in the refrigerator for later use.
Results and discussion
Preparation of magnetic PSS
Elemental analysis results
Adsorption performance of PSS magnetic materials
In these expressions, Qt is the adsorption amount (mg/g) at time t, Qe is the equilibrium adsorption amount (mg/g) of the material, and k1 (min−1) and k2 [g/(mg·min)] are the primary and secondary rate parameters, respectively.
The results of kinetics analysis
Initial SMR concentration (mmol/L)
K2 (g mg−1 min−1)
Pseudo first order kinetic model
ln(1 − Qt/Qe) = − 0.7013t + 0.7192
Pseudo second order kinetic model
t/Qt = 0.0301t + 10.0866
Fitting parameters of the Freundlich isotherm for SMR adsorption to PSS magnetic material
lnQe = 0.2857lnCe − 1.8923
Fitting parameters of the Langmuir isotherm for SMR adsorption to PSS magnetic material
Ce/Qe = 0.0271Ce+ 0.0018
In Eq. (5), Qm is the theoretical maximum adsorption amount (mg/g) of the material, and KL is the Langmuir adsorption equilibrium constant (L/mg). In Eq. (6), KF is the material adsorption capacity (mg/g), and n denotes the affinity of the material for the adsorbate. The results of the Langmuir and Freundlich isotherm adsorption equations are shown in Tables 3 and 4.
Thermodynamic parameters of adsorption
ΔS [J/(mol K)]
Testing in an actual food sample
Recovery results of spiked SMR in milk (n = 3)
Scaling amount (μg/mL)
PSS magnetic material was prepared by the SI-ATRP technique. The adsorption properties, thermodynamics, and kinetic parameters of the material were investigated in the presence of sulfa antibiotics. SMR (the smallest molecular-weight sulfonamide) was selected for analysis. At 25 °C and an initial SMR concentration of 0.6 mmol/L, the saturated SMR adsorption capacity of the magnetic material was 33.53 mg/g. The adsorption properties of the sulfa antibiotics on the material were well fitted by the Langmuir and Freundlich equations. According to the thermodynamic parameters, The thermodynamic parameters indicate that the adsorption process is a spontaneous endothermic process, and the elevated temperature is favorable for adsorption. Kinetic studies show that the adsorption process conforms to the quasi-second-order kinetic equation.
Authors would like to thank the National Natural Science Foundation of China for supporting this study.
HCL presented experimental research and edited manuscripts, YQZ and ZAS coordinated research and review manuscripts, and XXW and SWZ coordinated research and review manuscripts. All authors read the manuscript and participated in presenting the results and discussion. All authors read and approved the final manuscript.
This work was financially supported by the National Science Foundation of China (No. 21565001).
The authors declare that they no competing interests.
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