Photocatalytic degradation of polyethylene films using green-synthesized ZnO and Fe3O4 nanoparticles from Acacia nilotica

Abstract

This study reports the green synthesis of zinc oxide (ZnO) and iron oxide (Fe3O4) nanoparticles using Acacia nilotica (L.) leaf extract and their application in the photocatalytic degradation of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) films in aqueous medium. Phytochemical screening revealed that A. nilotica leaves contained high levels of phenolics (298.21 mg/100 g) and tannins (53.33 mg/100 g), providing strong reducing and stabilizing agents for nanoparticle formation. The synthesized ZnO and Fe3O4 nanoparticles exhibited UV–Vis absorption peaks at 385.09 and 467.92 nm with corresponding band gaps of 3.22 and 2.65 eV, confirming their semiconducting properties. Dynamic light scattering showed mean particle sizes of 13.64 nm (PDI 0.172) for ZnO and 19.21 nm (PDI 0.309) for Fe3O4, indicating uniform dispersion and good colloidal stability. XRD and HRSEM analyses confirmed their crystalline, well-defined morphologies, while EDX verified elemental purity. BET surface areas of 216.81 m²/g for ZnO and 199.41 m²/g for Fe3O4 suggested mesoporosity suitable for catalytic applications. Photocatalytic degradation studies revealed substantial polyethylene breakdown after 30 days under sunlight, with LDPE weight reduced to 73.07% (ZnO) and 74.90% (Fe3O4), and HDPE reduced to 91.20% and 91.76%, respectively. FTIR spectra of treated films showed the formation of carbonyl, hydroxyl, and C–O functional groups, while SEM images displayed surface cracks and cavities indicative of polymer chain scission. EDX spectra further confirmed Zn and Fe incorporation with intensified oxygen peaks, evidencing oxidative degradation. These findings demonstrate that A. nilotica-mediated ZnO and Fe3O4 nanoparticles are effective and sustainable photocatalysts for polyethylene degradation, offering a promising route toward eco-friendly plastic waste management.