Catalytic Behavior of Different Sizes of Dendrimer-Encapsulated Au_n Nanoparticles in the Oxidative Degradation of Morin with H₂O₂

Different sizes of icosahedral-like dendrimer-encapsulated Au nanoparticles (Au₅₅- and Au₁₄₇-DENs) were prepared in the presence of generation 6 amine-terminated dendrimers (G6-PAMAM-NH₂) as a template. The synthesis is carried out by the complexation of a Au metal precursor (AuHCI₄) with the tertiary amine groups within the dendrimer framework. The addition of excess reducing agent, NaBH₄, results in the formation of Au nanoparticles encapsulated within the dendrimer cavities. The as-prepared catalysts were characterized using UV-visible (UV-vis) spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDX), and Fourier transform infrared (FTIR). The average sizes of Au₅₅- and Au₁₄₇-DENs were determined to be 1.7 ± 0.4 and 2.0 ± 0.3 nm, respectively. The catalytic activity of these Au-DEN catalysts was evaluated in the oxidative decomposition of morin by H₂O₂. Since morin has a maximum absorption band at λ 410 nm at pH 10, this catalyzed oxidation process was monitored by time-resolved UV-vis spectroscopy. The catalytic activities of these two catalysts were compared by fitting the kinetic data to the Langmuir-Hinshelwood model. This model allows the determination of adsorption constants of both morin (K_morin) and H₂O₂ (KH₂O₂) on the catalyst surface. A full kinetic study for this Au-DEN-catalyzed oxidative degradation of morin is reported.