Bicontinuous Microemulsions for High Yield Wet Synthesis of Ultrafine Platinum Nanoparticles: Effect of Precursors and Kinetics

Abstract

We demonstrate that for high yield wet synthesis of monodispersed nanoparticles high surfactant content bicontinuous microemulsions offer an advantageous template as particle size is limited by the embedding matrix whereas particle aggregation is largely prohibited by its structure. We synthesized platinum nanoparticles varying the reaction rate, metal precursor and reducing agent type and concentration, and the composition of the microemulsion in water content and oil type. High yields of up to 0.4% of metal produced per weight of template were achieved without affecting the particle size, ca. 2 nm. We showed that our method is robust in the sense that particle size is hardly dependent on synthesis conditions. This is attributed to the fact that the packing of surfactant on nanoparticle surfaces is the only parameter determining the particle size. It can only be slightly varied with ionic strength, headgroup hydration, and tail solvency through oil variation. Water content mainly affects the microemulsion stability and through that the colloidal stability of the nanoparticles. Hydrazine as a reducing agent poses a special case as it causes dimerization of the surfactant and hence modifies the surfactant parameter as well as the stability. Finally, we highlighted the differences in comparison to nanoparticle synthesis in standard water-in-oil microemulsions, and we propose a mechanism of particle formation.

How to Determine the Core-Shell Nature in Bimetallic Catalyst Particles?

“…For the synthesis of core-shell particles in bicontinuous microemulsion the procedure described in [26] was adapted with a final, galvanic displacement step after synthesizing iron core nanoparticles, see Figure 3. The deposition of the shell material (Pt) was carried out by adding one microemulsion containing Pt-salt without further addition of reducing agent.…”

“…The key aspect of most microemulsion techniques is that waterphase nanoreactors can be tuned in size and yield monodispersed nanoparticles [4,25]. Recently, we have developed a synthesis method based on bicontinuous microemulsions that is capable of high yield production of ultrafine, monodispersed nanoparticles, see [26] and references therein. By expanding this method we have explored the possibilities of synthesizing also core-shell nanoparticles in a dense heptane/water/AOT bicontinuous microemulsion system.…”

Electrocatalytic Activity and Durability of Pt-Decorated Non-Covalently Functionalized Graphitic Structures

“…CNNs are 3D hyper-branched carbon graphitic structures organized in a nano-scale pattern. They can be easily produced by Chemical Vapour Deposition (CVD) of ethene over transition metal catalyst, used as nucleation elements, and synthetized in bicontinuous microemulsions (BME) [20][21][22]. The carbonization of the surfactant, being the primary carbon source, leads to the formation of networked, sponge-like, carbon graphitic structures (CNNs), which show promising properties for application as fuel cell supports, such as high electrical conductivity, great oxidation resistance, high specific surface area, micro-and meso-porosity, surface defects increasing the material ability to disperse in solution [11][12][13][14]19].…”

Synthesis of Nanostructured Catalytic Materials from Microemulsions

“…These very different processes are associated to a great range of catalytic materials. The microemulsion method, based on water-in-oil, oil-in-water and bicontinuous ME, has shown to be suitable for the preparation of all these different types of materials [12][13][14][15][16][17][18][19][20][21][22].…”

“…These very different processes are associated to a great range of catalytic materials. The microemulsion method, based on water-in-oil, oil-in-water and bicontinuous ME, has shown to be suitable for the preparation of all these different types of materials [12][13][14][15][16][17][18][19][20][21][22].Even though a few valuable efforts were previously done to understand the formation of nanomaterials in ME systems [23][24][25], comprehensive research in this area is still needed to clarify this process, in order to reach a better control of nanoparticle characteristics and to understand why the formed nanoparticles present specific catalytic properties compared to the materials with the same composition but prepared by traditional methods. Especially advanced analytical tools for deep…”