(490d) From Batch- to Continuous Flow Synthesis of Noble Metal Patches on Supports from Colloidal Particles up to Porous Bulk Materials

The preparation of nanoparticles of gold, silver or platinum have subject of intense study for several decades. A wide range of potential applications can be found e.g. in the fields of biomedicine, plasmonics, sensors or catalysis. Achieving controlled and scalable fabrication of asymmetrical particle morphologies by simple methods is a major hurdled to exploiting such materials, which are expected to have enhanced functionality. In the special case of patchy particles, the surface shows an inhomogeneous distribution of chemical and physical properties. Such situations might be achieved by depositing a material like gold, silver or platinum asymmetrically onto an initially homogenous surface. A well-known example of these relatively new types of particles are Janus particles which show a 50% surface contribution of different material and/-or functionality. Most of the fabrication methods for combining noble metals and non-metallic co-particles are based on the immobilization of spherical core particles onto a substrate to shadow a desired fraction of the particles surface against further chemical or physical treatments. Such approaches include several steps which lead to a high complexity and a limited scalability. In contrast, in our group we have developed a facile route to produce patchy particles which is based on the cooperative interaction of metal precursors and other reagents with a core particleâ??s surface. We have shown that this leads to a strong preference for heterogeneous nucleation and surface diffusion, leading to the surface conformal growth of noble metal patches. This general method can be applied to several patch- and co-particle combinations like Au@PS (polystyrene particles), Pt@PS and Ag@SiO₂. In this presentation it will be shown how this method has been introduced on the small scale in batch processes and further developed into a T-mixer based continuous flow process at different scales. Our results show that the mixing of the educts plays an essential role in the final particles properties like the distribution of metal loading at the co-particles surface â?? measured by analytical ultra-centrifugation (AUC), morphology and related plasmonic properties in the UV-VIS-NIR spectrum. By an increase of the core particle complexity by an increase of size and porosity as in case of catalyst support materials like porous glass particles, the limits of continuous flow synthesis at lab scale are given by the colloidal instability of the corresponding suspensions. We will show how these limits can be expanded by the use of a CSTR based process which allows the dispersion of the stock- and reactive suspensions by stirring. In addition, by the use of a mixing chamber where substrates can be immobilized, our general method allows the synthesis of novel metal patches on macroscopic porous materials such as silver patches on bio glass scaffolds in the millimeter scale.