Functional graphene-based magnetic nanocomposites as magnetic flocculant for efficient harvesting of oleaginous microalgae

Magnetic graphene oxide (GO) nanocomposite was assigned to decorate with cationic polymer PDDA (diallyldimethylammonium chloride) to a sponge like nanocomposite GO-Fe₃O₄/PDDA, and employed in magnetic harvesting of oleaginous Chlorella sp. HQ. The results showed that huge surface area, light weight and stable dispersion of GO make contribution to the high harvesting efficiency of GO-Fe₃O₄ (80.14%), compared to Fe₃O₄ NPs (62.65%) with 70 mg of nanomaterials / L of algal cells dose. In addition, graphene base provides more active sites to further decorate with PDDA, which imparts a positive zeta potential charge (21.94 mV) to nanoflocculants, thereby achieving 95.35% harvesting efficiency within 5 min. The adsorption followed Langmuir isotherm and pseudo-second-order kinetic model, with the maximum adsorption capacity of 14.06 g dry-biomass / g. Moreover, the harvesting efficiency decreased dramatically when pH increased for Fe₃O₄ NPs, while GO-Fe₃O₄and GO-Fe₃O₄/PDDA could maintain in a wide pH range. Besides,GO-Fe₃O₄/PDDA can be effectively reactivated (88.68% harvesting efficiency after 5 times reactivation) with 70 mg L^− 1 dose (add 30 mg L^− 1 after every time). It can be expected that this novel graphene-based magnetic nanocomposite has great potential to be a promising magnetic flocculant applied to efficient harvesting of oleaginous microalgae.