Abstract
During the processing of Juglans regia L., a large quantity of walnut green husk is produced as an agricultural byproduct. This residue exhibits significant biological importance, especially considering its natural antibacterial properties, which indicate its potential as a natural alternative to conventional antibiotics. In this work, the green husk of J. regia was extracted and characterized for its phytochemical profile, antioxidant potential, and content of total phenolics and flavonoids. It was then used as a reducing and stabilizing agent in the green synthesis of a CuO@CaO@Fe3O4 nanocomposite, resulting in nanoparticles approximately 90 nm in size. Phytochemical screening revealed that the extract contains diverse classes of bioactive molecules, including diterpenes, steroids, triterpenoids, coumarins, flavonoids, and various polyphenolic compounds. Quantitatively, phenolic compounds (62.67 μg GAE/500 μg extract) and flavonoids (38.61 μg QE/500 μg extract) are the predominant chemical categories. These naturally occurring molecules effectively coat the surface of the nanocomposite, significantly enhancing its antioxidant activity, with hydrogen peroxide scavenging ability surpassing that of vitamin C. Additionally, the synthesized CuO@CaO@Fe3O4 nanocomposite demonstrated notable antibacterial activity. In vitro assays confirmed its efficacy against both Gram-negative and Gram-positive bacterial strains, indicating promising prospects for biomedical and antimicrobial applications.