Metal-Ion Coordination Self-Assembled Green Synthesized Gold Nanoparticles for 4-Nitrophenol Reduction and Food Colorants Degradation

The field of responsive nanometric systems is rapidly expanding, offering significant potential for environmental and catalytic applications. In this study, we report the green synthesis of metal ion-directed self-assembled gold nanoparticles (AuNPs) mediated by <i>Pithecellobium dulce</i> (<i>P. dulce</i>) leaf extracts. This biosynthetic approach facilitates dynamic nanoparticle aggregation through metal-ion coordination, enhancing surface chemistry interactions and core nanoparticle organization. The precise molecular mechanism governing the self-assembly process remains to be fully elucidated. Nevertheless, these nanostructures (∼12 nm, face-centered cubic) exhibit remarkable catalytic activity, achieving near-complete reduction of 4-nitrophenol within 25 min and efficient degradation of azo food dyes, such as Tartrazine, Allura Red AC, and Brilliant Blue FCF, with removal efficiencies of up to 98%. Characterization by UV-visible, TEM, XPS and FTIR confirmed nanoparticle formation, biofunctionalization, and the potential interaction with target molecules. These results highlight the dual functionality of these green-synthesized AuNPs. They demonstrate their potential as versatile and environmentally friendly catalysts, as well as their high efficiency in water remediation, making them a promising solution to environmental challenges.