Effect of calcination temperature on the magnetic and biological behavior of green tea-assisted NiFe₂O₄ nanoparticles

The development of sustainable and cost-effective synthesis methods for multifunctional nanomaterials remains a significant challenge, as many conventional routes depend on toxic or expensive chemical precursors. In this study, nickel ferrite (NiFe₂O₄) nanoparticles were synthesized using green tea leaf extract as a natural bio-fuel, offering an eco-friendly alternative to traditional approaches. The influence of calcination temperature (350–750 °C) on the structural, magnetic, and biological properties of the nanoparticles was systematically investigated. X-ray diffraction and FTIR analyses confirmed the formation of a single-phase spinel structure, with crystallite sizes ranging from 14.15 to 39.76 nm. Vibrating sample magnetometry revealed a strong link between improved crystallinity and magnetic behaviour, with the highest saturation magnetization (86.06 emu/g) observed at elevated calcination temperatures. Biological assessments showed notable antibacterial activity against both E. coli and S. aureus . Cytotoxicity studies using A549 lung cancer cells demonstrated temperature-dependent anticancer activity, with comparisons against L929 normal fibroblast cells indicating differences in sensitivity. These results highlight the multifunctional behaviour of the green-synthesized NiFe₂O₄ nanoparticles and establish a clear connection between eco-friendly synthesis, thermal treatment, and resulting performance. The findings suggest that calcination-tuned, green-synthesized ferrites hold strong potential for applications ranging from magnetic sensing to therapeutic delivery. Future studies may explore in-depth mechanistic pathways and in-vivo performance to further validate their biomedical suitability. • Green synthesis of NiFe 2 O 4 nanoparticles using green tea via sol-gel auto-combustion. • Calcination (350–750 ℃) controlled cryatallite size (14–40 nm). • Magnetic properties varied non-monotonically with sintering temperature. • Sample at 750 ℃ showed high M s (86 emu g -1 ) and coercivity (218 Oe). • Nanoparticles exhibited antibacterial and anticancer activity.