Abstract Zinc ferrite (ZnFe2O4) nanoparticles have attracted the attention of researchers because of their unique chemical properties and particle-size-dependent magnetic properties. High-surface-area spinel ferrites have numerous technical applications in areas such as high-density information storage, ferrofluids, and catalysis. The coprecipitation technique is the preferred method for preparing nanoscale ZnFe2O4 because it results in a small crystals with a uniform size distribution. In this study, the synthesis was conducted in solution for 48 h, followed by sintering at 1000°C for 1.5–3.5 h. The smallest crystals (70.58 nm) were found in the sample sintered for 2.5 h. Fourier transform infrared spectroscopy (FTIR) functional-group analysis confirmed the presence of Fe–O and Zn–O bonds of cations in octahedral and tetrahedral sites. The ZnFe2O4 sintered for 3.5 h was superparamagnetic. The characterization results suggest that the obtained ZnFe2O4 could be used as a nanofluid in heat exchangers.

New Fe3O4/polyvinyl alcohol (PVA)/sodium alginate (C6H7O6Na)n nanohybrid ferrogels for antibacterial applications were fabricated. The crystal and molecular structures along with optical and magnetic properties of the prepared samples were characterized. The antibacterial activity of the ferrogels against Bacillus subtilis and Escherichia coli was investigated using the agar dilution method. X-ray diffraction analysis showed that the Fe3O4/PVA comprised a PVA amorphous phase and a spinel-structured Fe3O4 crystalline phase. The Fe3O4/PVA crystallite size was 7.5–9.9 nm and the scanning electron micrographs showed that the Fe3O4/PVA agglomerated. The ferrogels were superparamagnetic with saturation magnetizations from 14.8 × 10−3 to 82.1 × 10−3 emu/g. The absorption of the ferrogels showed a bathochromic effect, accompanied by an increase in the bandgap from 2.09 to 2.18 eV with increasing Fe3O4 content in the ferrogels. The ferrogels demonstrated new potency as antibacterial agents against B. subtilis and E. coli, where their antibacterial performance increased with increasing Fe3O4 content.

Abstract This study performs natural sand-based synthesis using the sonochemical route for preparing Zn-doped magnetite nanoparticles. The nanoparticles were dispersed in water as a carrier liquid to form Zn-doped magnetite aqueous ferrofluids. Structural data analysis indicated that the Zn-doped magnetite nanoparticles formed a nanosized spinel structure. With an increase in the Zn content, the lattice parameters of the Zn-doped magnetite nanoparticles tended to increase because Zn2+ has a larger ionic radius than those of Fe3+ and Fe2+. The existence of Zn–O and Fe–O functional groups in tetrahedral and octahedral sites were observed in the wavenumber range of 400–700 cm–1. The primary particles of the Zn-doped magnetite ferrofluids tended to construct chain-like structures with fractal dimensions of 1.2–1.9. The gas-like compression (GMC) plays as a better model than the Langevin theory to fit the saturation magnetization of the ferrofluids. The ferrofluids exhibited a superparamagnetic character, with their magnetization was contributed by aggregation. The Zn-doped magnetite ferrofluids exhibited excellent antibacterial activity against gram-positive and negative bacteria. It is suggested that the presence of the negatively charged surface and the nanoparticle size may contribute to the high antibacterial activity of Zn-doped magnetite ferrofluids and making them potentially suitable for advanced biomedical.