Magnesium aminoclay-Fe₃O₄ (MgAC-Fe₃O₄) hybrid composites for harvesting of mixed microalgae

In this paper, we describe the synthesis of magnesium aminoclay-iron oxide (MgAC-Fe₃O₄) hybrid composites for microalgae-harvesting application. MgAC-templated Fe₃O₄ nanoparticles (NPs) were synthesized in different ratios of MgAC and Fe₃O₄ NPs. The uniform distribution of Fe₃O₄ NPs in the MgAC matrix was confirmed by transmission electron microscopy (TEM). According to obtained X-ray diffraction (XRD) patterns, increased MgAC loading leads to decreased intensity of the composites' (311) plane of Fe₃O₄ NPs. For harvesting of Chlorella sp. KR-1, Scenedesmus obliquus and mixed microalgae (Chlorella sp. KR-1/ Scenedesmus obliquus), the optimal pH was 4.0. At higher pHs, the microalgae-harvesting efficiencies fell. Sample #1, which had the highest MgAC concentration, showed the most stability: the harvesting efficiencies for Chlorella sp. KR-1, Scenedesmus obliquus, and mixed microalgae were reduced only to ~50% at pH = 10.0. The electrostatic interaction between MgAC and the Fe₃O₄ NPs in the hybrid samples by microalgae, as confirmed by zeta potential measurements, were attributed to the harvesting mechanisms. Moreover, the zeta potentials of the MgAC-Fe₃O₄ hybrid composites were reduced as pH was increased, thus diminishing the microalgae-harvesting efficiencies.