Green synthesis of iron oxide nanoparticles using a mixture of Moringa oleifera Lam and Hibiscus sabdariffa L extracts and their application in photocatalytic degradation of methylene blue

Abstract

The development of sustainable nanomaterials via environmentally benign synthesis routes is critical to advancing green technologies for environmental remediation. In this study, iron oxide nanoparticles were synthesised via a green approach using a mixed aqueous extract of Moringa oleifera Lam leaves and Hibiscus sabdariffa L calyces as stabilising agents. The influence of extract ratios (1:1, 1:2, and 2:1) on the structural, optical, morphological, surface, and photocatalytic properties of the nanoparticles was systematically investigated. UV–visible spectroscopy confirmed nanoparticle formation of iron oxide nanocrystalline exhibiting band gaps between 3.0 and 3.6 eV. Fourier Transform Infrared Spectroscopy (FTIR) analysis verified the involvement of plant‑derived functional groups in nanoparticle stabilisation. Transmission electron microscopy (TEM) analyses showed formation of crystalline quasi‑spherical to irregular nanoparticles with sizes in the nano-regime. Powder X-ray diffraction (XRD) patterns of samples confirmed the formation of α‑Fe 2 O 3 with rhombohedral structure. Surface studies revealed mesoporous characteristics with a surface area of approximately 49.79 m² g⁻¹ . The photocatalytic performance of the synthesised nanoparticles was evaluated via degradation of methylene blue under UV irradiation, achieving up to 89% degradation within 120 min at low catalyst dosage (0.2 g L⁻¹). Kinetic studies indicated pseudo‑first‑order behaviour, while adsorption data were best described by the Freundlich isotherm model. These findings highlight the effectiveness of mixed‑extract‑mediated green synthesis in tailoring iron oxide nanoparticles with enhanced photocatalytic performance for wastewater treatment applications.