Facile biosynthesis of iron oxide nanoparticles from Parthenium hysterophorus extract and investigating their bioactive and photocatalytic applications.

Iron oxide nanoparticles (IONPs) were biosynthesized via a green co-precipitation method using aqueous extract of the invasive weed Parthenium hysterophorus, yielding particles with an average diameter of 14.65 ± 5.7 nm, as confirmed by TEM analysis. XRD revealed a pure crystalline phase with peaks at 2θ = 21.7°, 35.1°, 42.3°, 52.9°, 61.7°, and 69.3°, while SEM-EDS indicated a spherical morphology with 32.62% Fe and 34.97% O composition. DLS demonstrated a uniform distribution, and the zeta potential indicated stability. The IONPs exhibited potent antibacterial activity against Klebsiella pneumoniae, with an MIC of 1.56 µg/mL and an MBC of 6.25 µg/mL, resulting in inhibition zones of 3.4 mm (6.25 µg/mL) and 6.8 mm (12.5 µg/mL). However, they showed no activity against Staphylococcus aureus. Antifungal assays revealed significant inhibition of Fusarium sp. growth on Czapek-Dox agar after 4 days at 28 °C. In hydroponic plant growth studies, 20 mg/L IONPs enhanced Arachis hypogaea biomass by 20% (plant length), 15% (primary root length), and 25% (chlorophyll content), and Brassica juncea by 18% (primary root length), 22% (chlorophyll content), and 28% (fresh weight) over 14 days. Anti-hemolysis assays on human RBCs showed concentration-dependent protection with an IC50 of 600 µg/mL (hemolysis 14.37-37.6% at 600-1400 µg/mL). Photocatalytic degradation of Reactive Black 5 dye (10 - 5 M) achieved 99.57% efficiency in 60 min under sunlight (6.08 kWh m-2 intensity), following pseudo-first-order kinetics (k = 0.065 min⁻¹, R² = 0.997), with hydroxyl radicals identified as the primary reactive species via scavenging experiments (efficiency drop to 32.17% with IPA). Total organic carbon (TOC) analysis confirmed mineralization, as evidenced by a reduction in carbon content over time. This circular economy, also known as the waste-to-wealth approach, transforms invasive P. hysterophorus waste into IONPs for antimicrobial, agricultural, biomedical, and wastewater remediation applications.