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Transformer oil-based nanofluids have become popular research topic due to their enhanced dielectric and thermal properties. Considering the sustainability aspects of extending the life of transformer oil, it is imperative to conduct research on the effect of transformer oil with nanofillers. In the present work, the influence of conducting magnetite (Fe3O4), semiconducting titania (TiO2) nanoparticles and combination of Fe3O4 and TiO2 nanoparticles (multi-nanoparticle) on AC breakdown voltage are investigated for various concentrations. Nanofluid prepared using multi-nanoparticle shows enhanced AC breakdown voltage (BDV) of transformer oil compared with unfilled oil. Enhancement in BDV of 22% is observed with combination of 0.0025 wt% Fe3O4 and 0.0075 wt% TiO2. In addition, the effect of titania nanoparticles dispersed into service-aged transformer oil with a weight percentage of 0.01% is investigated. Comparative study of breakdown strength and viscosity of nanofluid with unfilled oil is performed. Service-aged oil sample shows increased BDV of 15% with TiO2 nanoparticles. The degradation in service-aged transformer oil is analyzed using UV–vis and Fourier Transform Infrared (FTIR) spectroscopy. The characteristics of oil samples are analyzed using fluorescence spectroscopy.

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The presence of greigite (Fe3S4) nanoparticles in bacterial magnetosomes, and its lower toxicity have emerged as favourable aspects for its potential applications in various bio-medical applications, including magnetic hyperthermia. Despite having a number of intriguing features, systematic research on the heating efficiency of Fe3S4 nanoparticles (MNPs) in an AC magnetic field is scarce, which is primarily due to the difficulties in preparing phase pure greigite MNPs. In this study, greigite MNPs are prepared using a solvothermal approach, utilizing ethylene glycol as a solvent, and surface functionalized with varied concentrations of poly vinyl alcohol (PVA). Studies using powder X-ray diffraction and electron microscopy demonstrate the development of crystalline Fe3S4 MNPs (average crystallite size: 19–23 nm) with flaky or flower-like morphology. X-ray photoelectron spectroscopy indicates that the lattice is composed primarily of iron and sulphur. The existence of bio-compatible PVA polymer on the surface of the coated MNPs is confirmed using Fourier transform infrared spectroscopy. For the uncoated MNPs, the magnetization at 90 kOe and the effective anisotropy energy density values are found to be ~ 5.2 emu/g and ~ 22.3 kJ/m3, respectively. Due to improved colloidal stability, magneto-calorimetric experiments reveal higher AC magnetic field induced heating efficiency for PVA-coated MNPs. The highest specific absorption rate (SAR) is obtained as ~ 67.8 ± 2.6 W/gFe in the current study, which is several times higher than the previously published values for synthetic Fe3S4 MNPs. Furthermore, for samples with comparable saturation magnetization and crystallite size, SAR is found to increase with initial susceptibility. The in vitro cytotoxicity studies show good bio-compatibility for the prepared greigite MNPs. The experimental findings provide deeper insights into the preparation of Fe3S4 MNPs using a simple solvothermal technique, and its AC magnetic field induced heating efficiency.

The advancements in magnetic nanoparticle mediated hyperthermia give so many optimistic and fruitful results that make it a promising and complementary approach for the existing treatment modalities of cancer. This thermotherapy is gaining wide acceptance among the medical community compared to the conventional treatment methods. The former provides a local heat generation in the malignant tumor cells and remains non-invasive to the adjacent healthy cells. The increased heating efficiency of magnetic nanoparticles and the control of local therapeutic temperature are the main challenges of hyperthermia. Superparamagnetic Iron Oxide nanoparticles have been intensively studied and dominating in magnetic hyperthermia. Recently many researchers successfully demonstrated high heating efficiency and biocompatibility of a wide variety of magnetic metal nanoparticles and proposed as the most promising alternative for traditional iron oxides, which opens up a new avenue for magnetic metal nanoparticles in magnetic hyperthermia. The review presents the recent advancements that occurred in the field of metal nanoparticle mediated magnetic hyperthermia. The theory underlying heat generation, synthesis methods, biofunctionalization, Specific Absorption Rate studies, challenges and future perspectives of magnetic metal nanoparticles are presented. This will inspire more in-depth research and advance practical applications of metal nanoparticles in magnetic hyperthermia.