FT-IR Investigation of the Thermal Decomposition of Poly(amidoamine) Dendrimers and Dendrimer−Metal Nanocomposites Supported on Al₂O₃ and ZrO₂

Abstract

The decomposition and removal of poly(amidoamine) (PAMAM) dendrimers from inorganic metal oxide surfaces frequently used as catalyst supports was investigated by the use of FT-IR spectroscopy. Spectra of fourth-generation hydroxyl-terminated PAMAM dendrimers (G4OH) on γ-Al 2 O 3 were collected first at room temperature and were subsequently analyzed with all bands assigned to the vibrational frequencies of dendrimer functional groups. Bands corresponding to amide and ethylenic groups decrease in intensity upon heating at 150°C, while new bands corresponding to surface carboxylate species appear in their stead. Thus, the process of dendrimer removal occurs in two stages: dendrimer decomposition to form adsorbed carboxylates followed by the removal of these carboxylates from the surface. The dendrimer generation (i.e., G3OH vs G4OH) does not affect the rate of this process. However, the temperature required for completion of the first stage rises with increasing G4OH weight loading. Other factors that influence the rate of overall dendrimer removal were found to include the type of gas-phase environment used and the presence or absence of metal species within the dendrimer. Specifically, an oxidizing environment, or the presence of either platinum or rhodium, facilitates complete dendrimer removal at lower temperatures. Finally, although the rate of dendrimer removal is very similar on both alumina and zirconia, the conformations of the adsorbed dendrimers on these supports are different.

Converting homogeneous to heterogeneous in electrophilic catalysis using monodisperse metal nanoparticles

“…Furthermore, recent reports that suggest more harsh conditions are required for complete dendrimer removal. 31,36,37 Regardless, Pt 40 proved to be the most robust catalyst and, after oxidative modification with PhICl 2 , maintained a steady rate of reaction, only to decrease as the reaction neared complete consumption of starting material ( Figure 2a). (Figure 2b).…”

Dependence of Gas-Phase Crotonaldehyde Hydrogenation Selectivity and Activity on the Size of Pt Nanoparticles (1.7–7.1 nm) Supported on SBA-15

“…For the investigation of gas-phase heterogeneous catalysis using polymer encapsulated NPs on oxide supports, the organic capping molecules are typically removed by thermal treatment (pyrolysis, combined calcination and reduction) [6,16,17].…”

Metal ion remediation by polyamidoamine dendrimers: a comparison of metal ion, oxidation state, and titania immobilization

“…Titania was selected for several reasons including its common use in wastewater processing for photocatalysis so it is already proven as stable under relevant and similar conditions. Adsorption of metal laden dendrimers is commonly examined for loading of nanoparticles onto metal oxide supports (e.g., silica (Castillo and Kuhn 2012;Huang et al 2008), alumina (Alexeev et al 2006;Deutsch et al 2007;Lopez-De Jesus et al 2008), titania (Crump et al 2008;Scott et al 2005), and zirconia (Deutsch et al 2007)) for the synthesis of heterogeneous catalysts. More in-depth studies also exist (Cahill et al 2008).…”

“…However, as will be discussed below, the dendrimer was shown to be stable on the titania. The bands associated with various dendrimer functional groups were analyzed via literature values (Deutsch et al 2004(Deutsch et al , 2007Ye et al 2004). The respective bands at 2,972, 2,921, and 2,849 cm -1 match asymmetric C-H methyl stretching, asymmetric C-H methylene stretching, and symmetric C-H methylene stretching.…”