Self-Assembly of Three-Dimensional Hyperbranched Magnetic Composites and Application in High-Turbidity Water Treatment

Abstract

In order to improve dispersibility, polymerization characteristics, chemical stability, and magnetic flocculation performance, magnetic Fe₃O₄ is often assembled with multifarious polymers to realize a functionalization process. Herein, a typical three-dimensional configuration of hyperbranched amino acid polymer (HAAP) was employed to assemble it with Fe₃O₄, in which we obtained three-dimensional hyperbranched magnetic amino acid composites (Fe₃O₄@HAAP). The characterization of the Fe₃O₄@HAAP composites was analyzed, for instance, their size, morphology, structure, configuration, chemical composition, charged characteristics, and magnetic properties. The magnetic flocculation of kaolin suspensions was conducted under different Fe₃O₄@HAAP dosages, pHs, and kaolin concentrations. The embedded assembly of HAAP with Fe₃O₄ was constructed by the N-O bond according to an X-ray photoelectron energy spectrum (XPS) analysis. The characteristic peaks of -OH (3420 cm^-1), C=O (1728 cm^-1), Fe-O (563 cm^-1), and N-H (1622 cm^-1) were observed in the Fourier transform infrared spectrometer (FTIR) spectra of Fe₃O₄@HAAP successfully. In a field emission scanning electron microscope (FE-SEM) observation, Fe₃O₄@HAAP exhibited a lotus-leaf-like morphological structure. A vibrating sample magnetometer (VSM) showed that Fe₃O₄@HAAP had a relatively low magnetization (Ms) and magnetic induction (Mr); nevertheless, the ferromagnetic Fe₃O₄@HAAP could also quickly respond to an external magnetic field. The isoelectric point of Fe₃O₄@HAAP was at 8.5. Fe₃O₄@HAAP could not only achieve a 98.5% removal efficiency of kaolin suspensions, but could also overcome the obstacles induced by high-concentration suspensions (4500 NTU), high pHs, and low fields. The results showed that the magnetic flocculation of kaolin with Fe₃O₄@HAAP was a rapid process with a 91.96% removal efficiency at 0.25 h. In an interaction energy analysis, both the U_DLVO and U_EDLVO showed electrostatic repulsion between the kaolin particles in the condition of a flocculation distance of <30 nm, and this changed to electrostatic attraction when the separation distance was >30 nm. As Fe₃O₄@ HAAP was employed, kaolin particles could cross the energy barrier more easily; thus, the fine flocs and particles were destabilized and aggregated further. Rapid magnetic separation was realized under the action of an external magnetic field.

Keywords: EDLVO; Fe3O4; hyperbranched polymer; magnetic flocculation; self-assembly.

Figure 1

The FTIR spectra of Fe₃O₄, HAAP, Fe₃O₄@HAAP.

Figure 2

The XPS spectra of Fe₃O₄@HAAP: (a) Fe 2p spectrum, (b) O 1s spectrum, (c) C 1s spectrum, (d) N 1s spectrum.

Figure 3

SEM images of Fe₃O₄@HAAP: (a) ×50; (b) ×2000; (c) ×10,000; (d) ×50,000.

Figure 4

The magnetization hysteresis loops of Fe₃O₄ and Fe₃O₄@HAAP.

Figure 5

Zeta potential of kaolin solution, Fe₃O₄, HAAP, and Fe₃O₄@HAAP.

Figure 6

Removing efficiency of Fe₃O₄@HAAP on kaolin solution under different conditions: (a) Fe₃O₄@HAAP dosage, (b) pH, (c) kaolin concentration, (d) reaction time.

Figure 7

Removing efficiency of Fe₃O₄@HAAP on actual water: (a) Lake 1, (b) Lake 2. The Fe₃O₄@HAAP dosage was 50 mg/L, pH = 5.

Figure 8

The recycling efficiency (a) and removing efficiency (b) of Fe₃O₄ and Fe₃O₄@HAAP on kaolin treatment under 5 recycling times, the colors correspond to different recycling times.

Figure 9

The interaction energy between Fe₃O₄@HAAP and kaolin: (a) kaolin–kaolin; (b) Fe₃O₄@HAAP–kaolin. pH = 5.