Green Synthesis of Passiflora foetida-mediated MnO₂ Nanoparticles for Rhodamine B Photodegradation, Antioxidant Activity and Gelatin Film Reinforcement

Abstract

Plant-assisted synthesis was adopted as a sustainable, uncomplicated, and economical approach for producing MnO₂ nanoparticles. Passiflora foetida leaf extract supplied phytochemicals that mediated the reduction of potassium permanganate and stabilised the resulting particles. UV–Vis spectroscopy, XRD, FTIR, and EDAX were employed to establish their formation, structure, surface chemistry, and elemental composition. A characteristic absorption band at approximately 285 nm supported MnO₂ formation. The XRD pattern revealed a nanocrystalline structure, with an average crystallite size of nearly 19 nm calculated using the Debye–Scherrer equation. FTIR analysis demonstrated the involvement of hydroxyl, carbonyl, and other plant-derived functional groups in particle formation and surface stabilisation, whereas EDAX confirmed manganese and oxygen as the predominant elements. Photocatalytic experiments produced a maximum Rhodamine B degradation efficiency of 97.8% at pH 7.0. Efficiency declined above the optimum dye concentration because concentrated solutions restricted light penetration and increased competition for reactive surface sites. The prepared MnO₂ nanoparticles also displayed considerable antioxidant activity, producing EC₅₀ values of 31.46 ± 1.08 µg/mL and 35.18 ± 1.15 µg/mL in ABTS and DPPH assays. Mechanical testing of MnO₂-reinforced gelatin films showed that formulation S5, containing 46 mL of gelatin solution and 4 mL of MnO₂ suspension (4000 µg MnO₂), achieved the highest elastic modulus of 845 MPa and tensile strength of 71 MPa. Overall, the developed nanomaterial demonstrated promising photocatalytic, antioxidant, and film-strengthening performance for sustainable wastewater-treatment applications.