Magnetically Recoverable Fe3O4-Cu Composite Particles with Strain-Dependent Antibacterial Activity

Abstract

Efficient water disinfection remains a critical challenge due to the persistence of waterborne pathogens. This study reports the synthesis and characterization of magnetically recoverable Fe3O4-Cu composite nanoparticles designed for efficient water disinfection. The particles consist of magnetite nanoparticles functionalized with metallic copper (Cu0) nanoparticles. The nanoparticles were synthesized via oxidative coprecipitation and characterized using x-ray diffraction, Mössbauer spectroscopy, DC magnetometry and transmission electron microscopy (TEM). Antibacterial assay was conducted against Staphylococcus aureus and Escherichia coli. Rietveld refinements confirmed lattice parameters and crystallite sizes of 8.40 Å (102 nm) for Fe3O4 and 3.62 Å (101 nm) for Cu. The 57Fe Mössbauer spectrum for Fe3O4, at 300 K, exhibited two sextets with isomer shifts and hyperfine magnetic fields of 0.61 mm/s (45.3 T) and 0.34 mm/s (48.9 T), corresponding to Fe2.5+ at octahedral sites and Fe3+ at tetrahedral sites, respectively. The isothermal magnetization at 300 K for Fe3O4 showed hysteretic behavior with saturation magnetization of 80.2 emu/g, remanence of 17.9 emu/g and coercivity of 197 Oe. Antibacterial efficacy was evaluated against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) using both the poisoned food method and batch removal assays. Results demonstrated a significant strain-dependent sensitivity; Fe3O4-Cu NPs inhibited S. aureus growth at concentrations as low as 0.1 mg/mL while E. coli required 0.5 mg/mL for similar effects. In batch experiments, 0.5 mg/mL of NPs achieved 100% bacterial removal for S. aureus, whereas 0.75 mg/mL was necessary for E. coli. Furthermore, the magnetic core facilitated rapid separation and reusability; the NPs maintained high efficiency against both strains in a second cycle, showing no significant loss of antibacterial activity. These findings highlight the potential of Fe3O4-Cu nanocomposites as high-performance, reusable biocides for targeted water treatment applications.