Gold Nanoparticles Synthesized Using <i>Citrus sinensis</i> Peel Extract: Photocatalytic Degradation of an Azo Dye and Antimicrobial, Antioxidant, and Anticancer Activities

ABSTRACT This study reports a green synthesis of gold nanoparticles (AuNPs) using Citrus sinensis peel extract as a bio‐reducing and capping agent with chloroauric acid (HAuCl 4 ) as the gold precursor. The successful formation of AuNPs was confirmed by ultraviolet–visible spectroscopy through the appearance of a characteristic surface plasmon resonance band. Structural properties were analyzed via x‐ray diffraction (XRD), while morphology, dimensions, and configuration were assessed using scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy (HR‐TEM). The biosynthesized AuNPs demonstrated considerable antibacterial efficacy and substantial antioxidant capacity in a concentration‐dependent manner. The AuNPs showed outstanding photocatalytic performance under visible light irradiation, degrading the crystal violet (CV) dye by 98.6% in 60 min. With an IC 50 value of 93.7 µg mL − 1 , cytotoxicity tests against MCF‐7 human breast cancer cells also demonstrated significant anticancer activity. Overall, this study presents an economical and environmentally friendly strategy for converting waste orange peel into functional AuNPs. The results highlight their strong potential for applications in photocatalysis, antimicrobial therapy, antioxidant activity, and cancer treatment.