Understanding the diffusion-driven colloidal deposition of laser-generated ligand-free nanoparticles on dispersed catalyst supports

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The new and further developments of nano-based catalysts has a great economic potential. A flexible method for the preparation of heterogeneous catalysts is the colloidal deposition of nanoparticles on support materials. Particle deposition can be initiated by electrostatically attractive interactions of charged particles in liquids. However, diffusion driven processes are also important, which can be observed in particular in the case of defect-rich carrier materials. While particle adsorption in the electrostatically attractive regime suggests an inevitably spontaneous and nonspecific deposition mechanism, a selective and specific adsorption is expected especially on defect-rich adsorbents, in the case of the electrostatically repulsive region. Thus electrostatically-driven particle adsorption causes agglomeration due to the high charge density, while in the electrostatically repulsive (diffusion-controlled) area the particles can be deposited homogeneously. Due to an existing energy barrier in the electrostatic repulsive region, the adsorption of several nanoparticles at the same time is unfavorable. These Aspects have been less studied in the literature, in particular for ligand-free conditions. Such ligand-free colloids are undoubtedly ideal model materials for colloidal particle dynamic investigations. Therefore, the aim of this project is to gain an understanding of the diffusion-driven particle adsorption by systematic investigations and thus to enable targeted control in the production of heterogeneous catalysts. On the basis of a well-founded hypotheses, an effect mechanism will be developed, which will describe the role of various surface defects on particle adsorption. For this purpose, ligand-free nanoparticles will be used and supports with different oxygen vacancies, facets and functional groups will be selected. Various characterization methods are used to elucidate the nanoparticle-defect interaction: photoelectron spectroscopy (particle oxidation, electronic structure, particle-carrier interaction), Raman spectroscopy (vibrational band of carrier-nanoparticle interaction), electron microscopy (particle size, shape and distribution), X-ray diffraction (crystal structure), IR spectroscopy (functional groups), thermogravimetry (particle mass loading), BET method (catalyst surface), UV-VIS spectroscopy (band gap, deposition efficiency, colloidal stability), measurement of zeta potential (colloidal stability, surface charge) and electrocatalysis (catalytic activity and stability ORR). Finally, by means of systematic studies a wide-ranging model to elucidate the mechanism of diffusion-driven particle deposition will be established and transferred to different material systems.