Biogenic Fabrication of Iron Oxide Nanoparticles Using <i>Tinospora cordifolia</i> Leaf Extract: A Green Approach for Enhanced Antioxidant Activity and Bio Adsorption, Reusability, Toxicity Analysis of Methylene Blue Dye

Phyto-synthesized iron oxide nanoparticles (Fe₃O₄-NPs) using Tinospora cordifolia (TC) leaf aqueous extract were investigated for their potential in adsorbing methylene blue dye (MB). TC-Fe₃O₄-NPs (T. cordifolia-synthesized iron oxide nanoparticles) were characterized using UV-Vis spectroscopy, FT-IR, XRD, and FESEM-EDAX. An absorption peak at 228 nm confirmed the synthesis, while FT-IR identified functional groups. XRD analysis verified the crystalline nature with prominent hkl planes at (220), (311), (400), (422), and (440). FESEM revealed a mean surface volume diameter of 82.21 nm. Adsorption studies showed optimal conditions with 10 ppm dye, 1 mg of adsorbent, 60 min of contact time, and pH 7. Under these conditions, the nanoparticles achieved a maximum adsorption efficiency of 88 ± 2.42% and a qmax of 104.49 mg g^-1, fitting the Langmuir isotherm model. Additionally, TC-Fe₃O₄-NPs exhibited antioxidant activity with IC₅₀ values of 77.56 ± 4.69 μg/mL and 28.67 ± 2.59 μg/mL in the DPPH and ABTS assays, respectively. The adsorbed dye was efficiently desorbed, enabling reusability for up to 5 cycles. Additionally, TC-Fe₃O₄-NPs demonstrated antioxidant activity, reducing dye-induced toxicity in Allium cepa roots and non-pathogenic bacteria, contributing to healthier root growth and enhanced bacterial viability. These findings highlight TC-Fe₃O₄-NPs as efficient, reusable adsorbents with potential environmental applications.