Harvesting of Chlorella vulgaris using Fe 3 O 4 coated with modified plant polyphenol

The Chlorella vulgaris harvesting was explored by magnetic separation using Fe3O4 particles coated with the plant polyphenol chemically modified by a Mannich reaction followed by quaternization (Fe3O4@Q-PP). The –N(R)4+ and Cl–N+–C perssad of the Q-PP were linked to the Fe3O4 particles by N–O bonds, as suggested by the X-ray photoelectron spectroscopy spectra. The thermogravimetric analysis displayed the mass percentage of the Q-PP coated on the Fe3O4 surface was close to ~ 5%. Compared with the naked Fe3O4 particles, zeta potentials of the Fe3O4@Q-PP particles were improved from the range of − 17.5~− 25.6 mV to 1.9~36.3 mV at pH 2.1~13.1. A 70.2 G coercive force was obtained for the Fe3O4@Q-PP composite, which demonstrated its ferromagnetic behavior. The use of Fe3O4@Q-PP resulted in a harvesting efficiency of 90.9% of C. vulgaris cells (3.06 g/L). The Fe3O4 particles could be detached from the cell flocs by ultrasonication leading to a recovery efficiency of 96.1% after 10 cycles. The recovered Fe3O4 could be re-coated with Q-PP and led to a harvesting efficiency of 80.2% after 10 cycles. The magnetic separation using Fe3O4@Q-PP included charge neutralization followed by bridging and then colloid entrapment.