Core-shell materials

A similar strategy was used to prepare BaFe12019-Ti02 core-shell materials, with the core of BaFei20i9 used to magnetically recover the catalyst and the shell ofTi02 that promoted degradation of dyes. The activity was dependent on the shell thick-... 

It has been predicted that a Pd skin on a PdsFe core would sit close to the top of the activity/O binding energy "volcano" curve and thus have significantly higher activity than Pt and Pt/Pd core-shell materials. If these materials could be shown to be stable to long-term PEM conditions, then these could represent viable replacements for Pt. As with other alternative non-Pt catalysts, very few stability studies have been reported. 

Presumably these three methods for preparing bimetallic, dendrimer-encap-sulated nanoparticles can be extended to trimetallics,bi- and trimetallics having unique structures (such as core/shell materials), and interesting combinations of two (or more) zero-valent metals plus intradendrimer ions. However, analysis of such materials await more sophisticated analytical methods than are currently at OUT disposal. 

It is possible to create more complex compounds and morphologies, such as alloys or core-shell structures. The nucleation step still occurs with injection of the metal carbonyl. However, when other organometallic precursors are in the solution, you can get the alloy to grow on the nuclei through transmetallation. To prepare core-shell material, the nuclei are allowed to react, then the temperature is reduced and a second precursor is introduced. The initial injection provided the nucleation which the additional materials when decomposed grow on the initial nuclei. 

Core/shell material Material state Oiquid/solid) Material density Material MW Equipment availability Material reactivity Pre/postprocessing Labor... 

Fleming MS, Mandal TK, Walt DR (2001) Nanosphere-microsphere assembly methods for core—shell materials preparation. Chem Mater 13(6) 2210-2216... 

To date core-shell nanomaterials based on PANI have been synthesized using PS, titanium oxide, gold, and vanadium oxide as seeds [275-283]. Various ways to nanometer-size PANI core-shell materials have been continuously developed, including ultrasonic irradiation polymerization, oxidative polymerization and electrochemical polymerization. 

With multiple phosphors, under ultraviolet excitation, the resulting color addition of red, green, and blue emissions in appropriate intensities produces white light. The primary color emissions need to be controllable, and the device must be efficient, cost-effective, and durable. One such method to produce white light uses downconversion in core-shell materials. This was achieved by employing Y2O3 Eu " core-LnP04 (Ln = Ce, Tb) shell micron-size particles [153] by the use of... 

This chapter will focus mainly on core-shell materials prepared by the addition of a Pt monolayer (PtML) to a preformed core, by various approaches (chemical and electrochemical), and consider the uniformity, stability, and activity of materials of... 

In addition to analysis by HAADF and elemental line scans, changes to the X-ray absorption near edge structure (XANES) may be investigated as a function of potential to investigate the structure of core-shell materials. Figure 19.4 shows results of these types of analysis for PtML/IrNi/C core-shell particles, where smaller changes in the XANES spectra vs. reference spectra at 0.41 V [plotted as (Ay — Aj o.4i)/Ay o.4i y axis. Fig. 19.4c] are observed for the core-shell compared to a Pt/C reference catalyst material. These data may be interpreted as a smaller change in Pt surface oxidation for the core-shell system, indicative of lower OH... 

Performance of Core-Shell Materials in Membrane Electrode Assemblies and Comparison with Rotating Disc Electrode... 

All these core-shell electrocatalysts show an improved Pt-based mass activity over Pt only which is maintained throughout the cycling test. However, the mass activities/g total PGM are not disclosed therefore, the overall cost reduction that might be expected from the use of these core-shell materials in MEAs is not clear. 

Gold lymCT nanocomposites were very stable, brush-type shells of linear macromolecules and terminal mesogen prepared by means of a quantitative termination reaction. The result was an amphiphilic core-shell material with a well-defined hydrophilic-lipophilic balance... 

Electrochemical leaching of Pt alloy catalysts has been deliberately applied to form core-shell materials with enhanced activities, either in half-cell tests [24, 25] or even... 

It is now clear how these hybrid core-shell materials present a very complex structure but also how, at the same time, they can assure the possibility of obtaining a great richness in functionalities, properties and performance [141]. 

Bimetallic dendrimers can be obtained by three prominent methods, inclnding cocomplexalion of metal salts, partial displacement, and sequential rednclion. These methods were comprehensively studied and reviewed before [4,14], The schematic representation of these methods is outlined in Fig. 6.3. The cocomplexalion method results in alloy-type bimetallics, while the other two methods can lead to alloy or core/shell materials depending on the identity of the two metals and the details of how the synthesis is carried out [15]. 

The classification scheme illustrated in Figure 13.1 contains many possible connections, not shown. For example, the latex core/shell materials and the latex IPNs differ principally by the presence of cross-links in the latter, but significant morphological and mechanical differences may also occur. The mechanochemical blends are synthesized when a polymer 1/monomer 2 mix is masticated with sufficient shear to degrade polymer 1 to a certain extent. The various free radicals, anions and cations formed then initiate the... 

Xiong Z, Zhang L, Zhao XS (2014) One-step synthesis of metal titania core-shell materials for visible-light photocatalysis and catalytic reduction reaction. Chem Eur J 45 1415-1420... 

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