Synthesis and catalytic investigation of dendrimer-derived colloidal and mesoporous supported transition metal (Ag, Au, Pt and Ru) nanoparticles in the reduction, oxidation and hydrogenation reactions

Ph.D. (Chemistry)Abstract: Spherical-like Au, Ag, Ru and Pt metal nanoparticles were synthesized using three different generations (G4, G5 and G6) of amine and hydroxyl-terminated poly(amidoamine) (PAMAM) dedrimers as a templating agent. Generation 6 amine-terminated PAMAM denrimers were used for the synthesis of Au nanoparticles (Au-DENs) using different dendrimer to metal molar ratio of 1:55 and 1:147. The resulted nanoparticles were denoted as Au55-DENs and Au147-DENs, respectively. Similarly, Generation 4 amine-terminated PAMAM dendrimers were employed for the synthesis of Au nanoparticles using dendrimer to metal molar ratios of 1:13 and 1:100. These nanoparticles were designated as Au13-DENs and Au100-DENs. Characterization of these DENs was carried out using UV-vis spectroscopy, HRTEM and EDX. The average particle sizes of Au55-DENs and Au147-DENs were determined to be 1.7 ± 0.4 and 2.0 ± 0.3 nm, respectively. The average particle sizes of Au13-DENs and Au100-DENs were determined to be 2.1 ± 0.3 and 3.1 ± 0.4, respectively. Generation 4 amine-terminated PAMAM dendrimers were used for the encapsulation of Ag and Au nanoparticles within silica nanosphere support. In that way, the dendrimer was acting as a dual templating agent for both the nanoparticles and the silica nanosphere. Dendrimer encapsulated or stabilized Ag or Au nanoparticles were prepared first, followed by the in situ encapsulation within the silica nanosphere. The average particle sizes of Ag and Au as determined by HRTEM prior to silica encapsulation were 3.3 ± 0.4 and 6.5 ± 1.0 nm, respectively. After silica encapsulation and calcination for the removal of dendrimer template, the average particle sizes increased to 3.6 ± 0.6 and 7.0 ± 1.0 for Ag and Au respectively. Characterization of these silica encapsulated Ag and Au nanoparticles was performed by UV-vis spectroscopy, HRTEM, EDX, SEM, FTIR, TGA, BET and PXRD. Generation 4 hydroxyl-terminated PAMAM dendrimers were used for the synthesis of Ru and Pt nanoparticles. Characterization of these prepared Ru and Pt-DEN catalysts prior to immobilization on mesoporous support materials was performed using UV-vis, HRTEM and EDX. The average particle sizes were determined to be 1.4 ± 0.2 and 1.7 ± 0.3 for Ru- and Pt-DENs, respectively. Immobilization of these DEN catalysts onto pre-formed mesoporous titania and silica support materials was carried out using wet-impregnation method. Mesoporous titania and silica materials were synthesized using P123 as a surfactant by a soft template method. These mesoporous supported Ru and Pt catalysts were further characterized using HRTEM, SEM, EDX, FTIR, TGA, BET, TPR and PXRD. Catalytic evaluation of Au55-DENs and Au147-DENs was performed in the oxidation of morin as a model reaction. This was carried out to investigate the effect of particle size on the catalytic..