Preparation and catalytic evaluation of ruthenium–nickel dendrimer encapsulated nanoparticles via intradendrimer redox displacement of nickel nanoparticles

Abstract

Ru and Ru x Ni 30 dendrimer encapsulated nanoparticles (DENs) were synthesized using a redox-displacement method. DEN catalytic activity for the reduction of p-nitrophenol was evaluated and found to be dependent on the ratio of metals present.Dendrimer-templated nanoparticle synthesis is an efficient method for preparing a variety of mono-and bimetallic nanomaterials, whose sizes are constrained by the loading capacity of the dendrimer template.1,2 A common commercially available dendrimer is composed of repeating amino-amide units (polyamidoamine, PAMAM), whose internal amines coordinate with free metal ions in solution.3 The metal ion affinity for these amine groups strongly influences their partitioning into the dendrimer interior; metal ions such as Cu 2+ and Pd 2+ will readily complex within dendrimers under the appropriate conditions and may be directly reduced to metal nanoparticles. 4,5 However, weakly coordinating metal ions require either a dendrimer template with more appropriate interior groups for coordinating metal cations, which may not be readily available, or an indirect synthetic route. Intradendrimer redox displacement, which involves the formation of dendrimer encapsulated nanoparticles (DENs) of one metal followed by exchange for a second, more noble metal, has been previously reported.6 Zhao et al. 6 synthesized Cu 55 DENs using generation 6, hydroxyl-terminated (G6-OH) PAMAM dendrimers. Here, we describe the preparation of ruthenium-nickel dendrimer encapsulated nanoparticles (RuNi DENs) in generation 4 hydroxylterminated (G4-OH) PAMAM dendrimers. Previously reported syntheses of Ru DENs used sodium borohydride (NaBH 4 ) 7 as well as H 2(g) 8 as reductants, following complexation of the Ru 3+ for 2-3 days. In this report, we investigated Ni as a potential partner in a displacement scheme to form Ru and RuNi DENs; the displacement was evaluated for 5-20 molar excess (ME) of Ru 3+ and Ni 2+ , and the resulting effects on the DEN catalytic efficiency for a model reduction reaction were evaluated. This method of preparation eliminates significant metal ion complexation time and results in RuNi DENs that are stable for at least a week under an inert atmosphere.The galvanic displacement of Ni 0 with Ru 0 is based on the following set of half-reactions:During synthesis, 30 ME of Ni(NO 3 ) 2 was added to a 10 mM aqueous solution of G4-OH PAMAM dendrimer at pH B5 and placed on a VWR nutating mixer. After 60-90 min, the UV-Visible absorption spectrum showed a very weak band at 272 nm and no bands associated with Ni 2+ in solution, indicating that (Ni 2+ ) 30 was complexed within the dendrimer interior (Fig. 1A). After purging with Ar (g) for 20 min, the solution was reduced with 5 ME of NaBH 4 ; the colorless solution turned translucent brown, the spectrum shifted upward, and the distinctive peak at 272 nm flattened. The solution pH was adjusted to r 8 using B0.010 mL (per mL of solution) of 0.10 M HCl via a gas-tight syringe; the approximate solution pH was checked using pHydrion paper. The soluti...

Dendrimer‐Encapsulated Cobalt Nanoparticles as High‐Performance Catalysts for the Hydrolysis of Ammonia Borane

“…These results indicate the formation of Co NPs, which is consistent with previous spectroscopic observations for other DENs 35. 36 The use of a mixture of AB and NaBH 4 as reducing agents results in amorphous non‐noble metal NPs, whereas the use of only NaBH 4 gives crystalline phase for non‐noble metals 22. 23, 25 The powder XRD measurements reveal no remarkable diffractions from Co NPs for these samples owing to the fine particle sizes (Figure S1).…”

A Small Change in Central Linker Has a Profound Effect in Inducing Columnar Phases of Triazine‐Based Unconventional Dendrimers

“…Dendrimers can be prepared by a convergent approach, first proposed by Vçgtle and co-workers, [1a] or a divergent approach, first proposed by FrØchet and co-workers. [1b] Recently, dendrimers have received great attention with regard to their potential use for various applications, for example as catalysts, [2] imaging agents, [3] light-harvesting molecules, [4] drug carriers, [5] nanoparticle stabilizers, [6] sensors, [7] and porous materials. [8] Dendrimers have also been observed to exhibit columnar liquid-crystalline (LC) phases and to be useful in photovoltaics and field-effect transistors [9] due to their non-grained boundaries and uniform alignments.…”

Catalytic Neutralization of Water Pollutants Mediated by Dendritic Polymers

“…Hydroxyl functionalized G6 additionally stabilized Au, Cu, Pd, Pt, and Au-Cu, Pd-Cu, Pt-Cu bimetallic NPs with smaller diameters in the range of 1 to 3 nanometers and established the beneficial synergistic effect of Ag or Cu combination with a more expensive noble metal to the reaction rate [80]. The analogous outcome was created when PAMAM-OH G4-G6 were employed to generate Ru NPs with mean diameters ranging from 1.1 to 2.2 nm [81] and to amalgamate Ru and Ni with the bimetallic combination manifesting superior performance that single metal equivalents [82].…”