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Functionalization of Nanoparticles (NPs) with Hydrophilic Ligands

A New Perspective for the Control of Chemo- and Stereoselectivity in Heterogeneous Catalysis

The functionalization of metal nanoparticles with organic molecules (ligands) shows a growing interest in the field of heterogeneous catalysis, as ligands allow for the tuning of selectivity.1 For applications in liquid phase the ligand properties are however crucial. Particles that are functionalized with lipophilic ligands are applicable as “quasi-homogeneous” catalysts in organic media due to attractive interactions between the ligand shell and the solvent. For the same reason they cannot be used as supported, heterogeneous catalysts, because the ligand solvent interaction forces them to desorb from the support to form a colloidal dispersion.

To overcome these limitations we developed a synthesis route for the functionalization of Pt nanoparticles with hydrophilic, chiral ligands.2 So-called “unprotected” nanoparticles are synthesized (see step 1 in Fig. 1) according to procedure that allows for the control of metal and size.3 These “unprotected” nanoparticles are subsequently functionalized in a separate step (see step 2 in Fig. 1) and deposited after preparation on a given support material (see step 4 in Fig. 1). This concept allows for the independent control of particle, ligand, and support and thus to study systematically their influence on the catalytic properties.

Functionalization of NP Figure 1. First, “unprotected” nanoparticles (NPs, grey) are prepared and subsequently functionalized (step 2) with ligands (yellow). Various experimental techniques (aberrations used) can be applied to characterize these materials (step 3). After particles deposition onto support materials (orange-brown) the materials are applicable as heterogeneous catalysts.

The functionalized nanoparticles can be isolated as pure materials and redispersed allowing for the application of various characterization techniques. We routinely apply transmission electron microscopy (TEM) to estimate the particle size and elemental analysis (EA) in combination with atomic absorption spectroscopy (AAS) to determine the ligand coverage.2 The properties of the ligand shells are investigated by means of IR- and NMR spectroscopy (see step 3 in Fig. 3).4
Using the above described preparation concept our research focuses on investigating nanoparticles functionalized with hydrophilic ligands as chemo- and stereoselective, heterogeneous catalysts in a systematic way. By this we aim to elucidate how the different material parameters (particle, ligand, support, and reaction conditions) influence the catalytic properties to elucidate how the catalytic properties of ligand-functionalized nanoparticle can be tailored.

Imke Schrader, Sebastian Kunz

References

1 S. T. Marshall, M. O’Brien, B. Oetter, A. Corpuz, R. M. Richards, D. K. Schwartz and J. W. Medlin, Nat. Mater., 2010, 9, 853-858.

2 S. Kunz*, P. Schreiber, M. Ludwig, M. M. Maturi, O. Ackermann, M. Tschurl and U. Heiz, Phys. Chem. Chem. Phys., 2013, 15, 19253-19261.

3 Y. Wang, J. W. Ren, K. Deng, L. L. Gui and Y. Q. Tang, Chem. Mater., 2000, 12, 1622-1627.

4 S. Kunz*, M. M. Maturi, I. Schrader, J. Backenköhler, M. Tschurl and U. Heiz, J. Colloid Interface Sci., 2014, 426, 264-269.

Cooperation partner: V. Azov, Institute for Organic Chemistry, Universität Bremen

Funding: Fonds der Chemischen Industrie (FCI)

For detailed information contact Sebastian Kunz

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