Magnetic Fe3O4-polyethyleneimine nanocomposites for efficient harvesting of Chlorella zofingiensis, Chlorella vulgaris, Chlorella sorokiniana, Chlorella ellipsoidea and Botryococcus braunii

Abstract A reduction in energy consumption at every stage of the down streaming process is needed to make 3rd generation of biofuels economically viable. In this study, magnetite (Fe 3 O 4 ) nanoparticles were synthetized by coprecipitation of FeCl 2 and FeCl 3 in alkaline medium at two different temperatures. The particle sizes were 11.5 ± 4 and 9.5 ± 4 nm for the nanoparticles prepared at 80 °C and 25 °C, respectively. The adsorption of polyethyleneimine (PEI) onto Fe 3 O 4 was studied by equilibrium batch measurements. A mono-layer absorption of PEI was found. The Fe 3 O 4 –PEI nanocomposites had a positive zeta potential, which decreased with increasing pH of the solution. The nanocomposites were used for magnetic harvesting of negatively charged Chlorella zofingiensis , Chlorella vulgaris , Chlorella sorokiniana , Chlorella ellipsoidea and Botryococcus braunii microalgae strains. Upon dosage of 200 mg/L of Fe 3 O 4 –PEI harvesting efficiencies of 68–97% were achieved at pH 4 within 1 min. The harvesting efficiency decreased with increasing pH of the suspension. The results demonstrate that Fe 3 O 4 nanoparticles synthesized at the lower temperature (25 °C) could be used for an efficient magnetic harvesting of different microalgae strains. The lower synthesis temperature may thereby contribute to the cost reduction of microalgae harvesting.