Preparation Of Magnetic Chitosan And Study On The Adsorption Of Perfluorooctane Sulfonate In Water

Perfluorooctane sulfonate (PFOS) with high-energy carbonefluorine (C-F) bonds is a typical perfluorinated compounds. Because of its exceptionally high stability, PFOS is difficult to decompose by heat, oxidation and reduction, biological degradation. Chitosan, alkaline deacetylated products of chitin, can be easily chemically modified due to the exsistance of hydroxyl and amino groups. In this paper, the preparation and characterization of magnetic chitosan (MCTS) adsorbent were systematically studied. In addition, the removal of PFOS from water by MCTS as well as the adsorption mechanisms were also examined in detail.MCTS was prepared by emulsion suspension polymerization method with the Fe3O4 acting as magnetic materials, which was prepared by solvothermal method. Simultaneously, the preparation conditions were optimized comprehensively. The elution and regeneration performance of MCTS were studied after the adsorption process.Fe3O4 and MCTS were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), Zeta potential and particle size analysis. Main conclusions were summarized as follows:① Fe3O4 and MCTS enjoyed good thermal and magnetic performance, and dispersed evenly in the water with smooth surface, the average particle size were 274 nm and 4.8 μm, respectively.② Fe3O4’s peaks appeared in the XRD spectrum of MCTS. In addition, chitosan’s peak shape was embodied in FT-IR spectra of MCTS, especially its characteristic peak of 1643cm-1 represent schiff base (-C=N-). Results proved that Fe3O4 was coated with chitosan. ③ By zeta potential analysis of MCTS, pH at the MCTS zero isoelectric point was about 2.95.Factors such as adsorption time, initial concentration, adsorbent dosage, initial pH, temperature and the concentration of NaCl were investigated in the adsorption experiment. Rseults were as follows:① Adsorption kinetics curve of MCTS was in line with secondary kinetic curve, adsorption isotherm curve of MCTS was in line with the Langmuir model. Adsorption capacity of PFOS by MCTS topped 1250 mg/g at 25 ℃. ② Adsorption capacity of MCTS was heavily impacted by pH and ionic strength of the salt while less affected by temperature. pH<7 and higher ionic strength of the salt were conducive to the adsorption process. According to the thermodynamics analysis, the adsorption process was an exothermic reaction.Factors such as the eluent category, the eluent proportion, the concentration of NaOH and the elution time were explored in the elution and regeneration experiments. Results showed:① Optimum eluant was 0.1 mol/L NaOH/acetone (v/v=1/1) mixture. ② Adsorption efficiency remained unchanged basically after five times of adsorption-regeneration process.In the determination of PFOS in tap water, Youyi River, Zixia River, the recovery values of MCTS were in the range of 91.0～93.7%,89.1～92.4%,89.5～92.9%, respectively. Results indicated that MCTS showed good adsorption capacity in actual water samples.