Amine-Functionalized Maghemite Nanoflowers for Efficient Magnetic Removal of Heavy-Metal-Adsorbed Algae

This study aimed to clarify the interactions between cobalt-adsorbed Chlorella vulgaris cells and amine-functionalized maghemite nanoparticles, focusing on nanoparticle adsorption to the algal surface and the subsequent magnetic sedimentation of the formed complexes. The combined process of cobalt uptake by algae and secondary binding of magnetic nanoparticles demonstrates a promising and sustainable strategy for heavy metal removal from industrial wastewater. The adsorption capacity of Chlorella vulgaris was assessed, achieving 96 ± 2% Co2+ removal, followed by magnetic separation using γ-Fe2O3 nanoparticles. The subsequent magnetic separation of the cobalt-adsorbed biomass achieved efficiencies ranging from 57.43% to 97.64% within a 60 s timeframe, demonstrating a significant enhancement over conventional sedimentation methodologies. Stable nanoparticle–biomass binding was facilitated by electrostatic interactions between protonated amine groups on the surface of amine-functionalized maghemite particles and the negatively charged functional groups of the algal cell wall, complemented by the contribution of hydroxyl and carboxyl groups. The even distribution of amine-functionalized maghemite nanoparticles on algal surfaces was further validated by Transmission Electron Microscopy (TEM) imaging, and the strong magnetic properties of the nanoparticles enabled rapid and efficient separation under an external magnetic field. This study underscores the promise of integrating Chlorella vulgaris with amine-functionalized maghemite nanoparticles as a cost-effective, biocompatible, and environmentally sustainable approach for large-scale heavy metal removal from industrial wastewater.