Jessi van der Hoeven MSc
Ornstein Laboratory, room 0.12 / DDW 4th floor
Princetonplein 1, 3584 CC Utrecht
P.O. Box 80 000, 3508 TA Utrecht
phone: +31(0)30 253 2925
secretariat: +31(0)30 253 2952
Promotors: Prof. P.E. de Jongh and Prof.dr. A. van Blaaderen
Employed since December 2014
Funded by NWO
Self-assembly of stable gold-based catalysts
Similar to atoms in conventional solids, nanoparticles can be used as building blocks to construct larger so-called superstructures. In this project, catalytically active metal nanoparticles (Au-based) are self-assembled with oxide colloids into ordered superstructures. The nanoparticles spontaneously form an ordered colloidal crystal when gradually evaporating the surrounding solvent. Dispersing the nanoparticles in oil droplets rather than a continuous phase results in the formation of spherically shaped superstructures [Figure 1a]. Such well-defined systems can serve as model catalysts of which the composition, size and placement of the components can be tuned with great precision.
The aim of the project is twofold. First, we want to synthesize a set of binary colloidal crystals, identify the different crystal structures and thereby gain a deeper insight in the nucleation of binary crystals, a fundamental issue in soft matter science that is still largely unsolved. Second, we want to study the catalytic properties of these colloidal crystals, in particular the relationship between the crystal structure and the catalytic stability. We expect that the degree of encapsulation of the Au nanoparticles either by neighboring silica nanoparticles or directly with a silica shell [Figure 1b] will prevent particle growth and sintering during catalysis and will thus enhance the catalytic stability. In addition, the melting temperature of gold-based nanoparticles in the colloidal crystal as a function of the crystal structure will be measured.
Colloidal synthesis, electron tomography (3D-TEM), Energy-dispersive X-ray spectroscopy (EDX)
Nowadays metal nanoparticles (NPs) are widely used in industry as heterogeneous catalysts, for data storage, biomedical- and optical applications. So far, most catalysis related studies focused on isotropic, spherical nanoparticles. In this project, we will investigate the catalytic properties of anisotropic nanoparticles: gold-based nanorods. Unlike gold spheres, nanorods have a strong longitudinal surface plasmon resonance (LSPR) in the visible or near-infrared range of the spectrum. By altering the shape, the dimensions (aspect ratio) or composition of the rod, the LSPR can be tuned.
The overall aim of the project is to investigate Au-based nanorods as a model system for catalysis. We study the relationship between the exposed surface facets and catalytic properties by varying the dimensions (aspect ratio) of the rod to identify the most active surface facets. Secondly, we want to study the effect of the surface plasmon resonance on the catalytic properties of the AuNRs. The third aim of the project is to investigate the catalytic behavior of bimetallic nanorods. We developed a new method to synthesize AuAg, AuPd and AuPt core-shell nanorods of which the shell-thickness and surface morphology can be controlled precisely. These core-shell particles can then be homogeneously mixed into alloyed nanorods without losing the anisotropy, via thermal treatment. For catalysis such multicomponent systems are particularly interesting when synergetic effects come into play. Several examples are known where the combination of two metals gives a catalytic activity that is significantly higher than those of the individual metals.
Figure 1 – From left to right: silica coated Au nanorods, AuAg and AuPd core-shell nanorods of which the aspect ratio, shell-thickness and surface morphology can be tuned