Multifunctional oleic acid functionalized iron oxide nanoparticles for antibacterial and dye degradation applications with magnetic recycling

Abstract

Nanotechnology that synchronously mitigates biomedical and environmental challenges is imperative for sustainable innovation. In this study, we report the synthesis of oleic acid (OA)-modified iron oxide (Fe₃O₄) nanoparticles via co-precipitation, which exhibit potent bactericidal effects and rapid photocatalytic dye degradation. Their intrinsic magnetic properties enable efficient recovery and repeated reuse, offering a robust platform for integrated remediation strategies. Comprehensive characterization confirmed that the synthesized OA-functionalized Fe₃O₄ nanoparticles (NPs) possess a single-phase cubic structure (12.17 nm crystallite size), an intact OA coating with particle size 13.01 nm, direct/indirect band gaps of 3.58/2.54 eV, and superparamagnetic behaviour exhibiting 40 emu g⁻¹ saturation, confirming advanced functionality. The OA-coated Fe₃O₄ NPs exhibited a high zone of inhibition (ZOI) of 9.28 mm against Escherichia coli DH5α bacteria at a low concentration of 50 μg μL⁻¹, surpassing similar ferrite-based systems. The strong antibacterial activity is attributed to the generation of reactive oxygen species (ROS) and the controlled release of Fe²⁺/Fe³⁺ ions, which disrupt the bacterial cell membrane, denature proteins, and damage DNA. The superparamagnetic nature of the NPs ensures minimal coercivity and remanence, facilitating precise targeting and magnetic separation in biomedical applications. Moreover, the OA-coated Fe₃O₄ NPs achieved 99.17% degradation of Rhodamine B (RhB) dye under visible light irradiation in 340 minutes. This performance is rooted in the synergistic effects of OA, which enhances light absorption and electron–hole pair separation, and Fe₃O₄, which drives redox reactions through its conduction band electrons and valence band holes. The photocatalytic degradation follows first-order kinetics, with a rate constant of 0.0079 min⁻¹. Importantly, the magnetic properties of the NPs allowed efficient recovery and reuse for four consecutive cycles, demonstrating long-term stability and economic viability. This study underscores the interplay between surface functionalization, magnetic behaviour, antimicrobial and catalytic properties, establishing OA-coated Fe₃O₄ NPs as a potent, cost-effective solution for dual-action biomedical and environmental applications.