Preparation Of Magnetic Chitosan And Study On The Adsorption Of Trifluoroacetic Acid In Water

Trifluoroacetic acid (TFA) with high-energy carbonefluorine (C-F) bonds is a kind of perfluorinated compounds. Because of its exceptionally high stability, TFA is difficult to be decomposed by heat, oxidation or reduction and 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 was systematically studied. In addition, the removal of TFA from water by MCTS as well as the adsorption mechanisms was 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 270 nm and 4.5 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 3.0.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 TFA by MCTS topped 70 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 TFA in tap water, Zixia River, the recovery values of MCTS were in the range of 89.3～93.9%,90.5～92.9%, respectively. Results indicated that MCTS showed good adsorption capacity in actual water samples.