Catalytic activity of different sizes of Pt _n /Co ₃ O ₄ in the oxidative degradation of Methylene Blue with H ₂ O ₂

In this work, we demonstrate the catalytic activity and kinetic analyses of generation six poly(amido-amine) hydroxyl-terminated (PAMAM), G6-OH(Pt _n ) (n = 55, 140, 225) dendrimer-encapsulated nanoparticles (DENs) immobilized onto mesoporous cobalt oxide (Co ₃ O ₄ ) for the catalytic oxidation of methylene blue (MB). Ultra-Violet Visible (UV–Vis) spectrophotometry showed the ligand to metal charge transfer (LMCT) band of metal precursor ions coordinated to the tertiary amines of the dendrimer. The size of fully reduced Pt DENs and supported Pt nanoparticles were investigated using High-Resolution Transmission Electron Microscopy (HR-TEM). The mesoporous Co ₃ O ₄ was synthesized by inverse micelle method, prior to Pt _n DENs being supported on the Co ₃ O ₄ via wet impregnation procedure. The crystallite structure and size of Co ₃ O ₄ was investigated by powder X-ray diffraction (p-XRD) spectroscopy. Immobilized Pt _n /Co ₃ O ₄ structural analysis was investigated for the pore size and pore volume using N ₂ sorption techniques. Thermal gravimetric analyses (TGA) also indicated the dendrimer decomposition on the G6-OH(Pt _n )/Co ₃ O ₄ materials to be 550 °C. Hydrogen temperature programmed reduction (H ₂ -TPR) analyses were conducted and the reducibility of the supported cobalt oxide showed only one temperature peak that was ascribed to the reduction of surface lattice oxygens. The experimental kinetic data was analyzed and fitted to the Langmuir-Hinshelwood model using elementary first-order reaction kinetics and the thermodynamic parameters were calculated. Catalyst Pt ₅₅ /Co ₃ O ₄ showed stability during the reusability investigation of up to 8 cycles. The G6-OH(Pt _n ) were immobilized on silica and tested for catalytic oxidation of MB as a control experiment.