β-cyclodextrin functionalized gold nanoparticles as an effective nanocatalyst for reducing toxic nitroaromatics

We demonstrated the effective reduction of the organic pollutants, the nitroaromatics, via green sustainable chemistry using high efficacy of the catalytic materials, i.e., β-cyclodextrin (β-CD) functionalized Au nanoparticles (AuNPs). Eco-friendly and biocompatible techniques were employed to fabricate gold nanoparticles (AuNPs) from an Au precursor (HAuCl4) using β-CD that plays as both reducing and surface-functionalizing agents. Detailed investigation of β-CD AuNPs formation, their sizes with morphologies, the surface charge, and the hydrodynamic size in a colloidal medium were performed by ultraviolet–visible (UV–vis) absorbance spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Zeta potential measurements, and the dynamic light scattering analysis, respectively. The plasmonic nanoparticle formation of the β-CD AuNPs led to the strong localized surface plasmon resonance peak at around the 520 nm wavelength. The catalytic activity of the β-CD AuNPs was evaluated using model reactions, including the catalytic conversion of nitroaromatics to the corresponding amino-aromatic compounds upon mixing sodium borohydride in a water medium. Chemical reactions of such catalytic reduction of nitroaromatics were tracked by UV–vis absorbance spectroscopy, showing high catalytic activity of β-CD AuNPs. We also provided a discussion on the possible pathways for the AuNPs-mediated catalytic reduction of nitroaromatics. The efficacy of the nanocatalysts presented to reduce nitroaromatics can hold a potential promise for detoxifying aquatic environments and their pharmaceutical applications.