Mechanism of the Formation of Amorphous Gold Nanoparticles within Spherical Polyelectrolyte Brushes

Abstract

We present a comprehensive investigation on the formation of gold nanoparticles in spherical polyelectrolyte brushes. These colloidal carrier particles consist of a solid polystyrene core onto which long cationic polyelectrolyte chains are grafted. Immersed in water these polyelectrolyte chains can be used to enrich AuCl ions. The metal ions thus confined in the polyelectrolyte layer can be reduced to gold nanoparticles of approximately 1 nm diameter. Cryogenic transmission electron microscopy shows that the Au particles are located near the surface and exhibit a narrow size distribution. Measurements by dynamic light scattering demonstrate that the polyelectrolyte chains are located near the surface of the core particles. This is explained by a crosslinking of the cationic polyelectrolyte chains by the nanoparticles that carry a negative charge. If the Au nanoparticles are removed, the spherical polyelectrolyte brushes re‐expand. High‐resolution electron microscopy together with wide‐angle X‐ray scattering measurements demonstrates that the Au nanoparticles are amorphous. We demonstrate that these Au nanoparticles exhibit catalytic activity for hydrogenation reactions that is slightly below the one of Pt and Pd nanoparticles.magnified image

Improving gold catalysis of nitroarene reduction with surface Pd

“…Figure 4 plots the activation energy results as well as the TOF of the catalysts. As can be seen, the activation energy results for the catalysts are within the range previously reported for metallic catalysts (7.5 kJ/mol -110 kJ/mol) [11,14,[39][40][41][42]. The monometallic Au NPs had an activation energy of 12.7 kJ/mol.…”

Reduction of 4‐Nitrophenol as a Model Reaction for Nanocatalysis

“…Wunder et al [63] reported an E A of 40 kJ·mol -1 for the normalized rate constant of Pt NPs immobilized onto a cationic spherical polyelectrolyte brush. Th is was in good agreement with their previous work using the same carrier system for metal NPs, where the E A was found to be 44 kJ·mol -1 [60,61,92]. Th ey demonstrated that the E A refl ects the temperature dependence of the kinetic constant k app and of the two thermodynamic adsorption constants K 4-NP and K BH 4 -.…”

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