This paper describes a simple approach to the synthesis of asymmetric, hybrid colloidal particles by precipitation polymerization. The key is to introduce Au or Ag colloids 2 min after (rather than before) starting the polymerization. The hybrid particles were uniform in size, and each one of them only contained one Au (or Ag) nanoparticle in its surface. Due to the simplicity of this procedure, it should be possible to use it for large-scale production. This method can be extended to metal nanoparticles other than Au and Ag and with a range of sizes, as long as they have appropriate charges on the surface. xia@biomed.wustl.edu. Increasing attention has been paid to colloidal particles with an asymmetric, hybrid structure because of their use in applications such as fabrication of optical, optoelectronic, and sensing devices through the "bottom up" approach. 1 Many efforts have been devoted to the synthesis of asymmetric, hybrid colloidal particles, and approaches include surface selective modification, 2 template-assisted self-assembly, 3 phase separation, 4 surface-controlled nucleation and growth, 5 and microfluidic techniques. 6 In spite of the success, it is worth pointing out that most of these methods cannot be easily applied to large-scale production because of the two-dimensional strategy or multiple steps involved in a typical fabrication process. Still, a facile and robust procedure is desired for the preparation of asymmetric, hybrid colloidal particles. NIH Public AccessHere we report a simple and versatile procedure for generating asymmetric, hybrid particles consisting of metal nanoparticles and polymer beads. We simply modified precipitation polymerization of polystyrene (PS) by adding Au (or Ag) colloids into the system after the polymerization had proceeded for a few minutes. The asymmetric particles were uniform in size and morphology, with each PS bead containing only one Au or Ag nanoparticle in its surface. Scheme 1 shows a schematic illustration of the procedure we used for generating the Au-PS asymmetric, hybrid particles. We firstly added styrene and divinylbenzene (DVB) to a mixture of ethanol and water, in which 4-styrenesulfonic acid sodium salt (NaSS) and potassium persulphate (KPS) had been dissolved. Since NaSS and KPS could stabilize the growing PS beads, we did not introduce other surfactants into the reaction system. After 2 min into the synthesis at 70 °C, we introduced Au colloids (50 nm in diameter) into the reaction mixture. At this point, PS oligomers and/or monomers started to nucleate by adsorbing onto the surface of Au nanoparticles, then grew in size, and eventually evolved into spheres as confined by surface tension. After 4 h into the reaction, the final product of hybrid particles was harvested by centrifugation and repeated washing with a mixture of ethanol and water. Figure 1 shows SEM and TEM images of the as-prepared Au-PS asymmetric, hybrid particles. The particles were slightly nonspherical in shape, but uniform in size with an average diameter of 300 n...

Colloidal gold (Au) nanoparticles were prepared and successfully loaded on titanium(IV) oxide (TiO(2)) without change in the original particle size using a method of colloid photodeposition operated in the presence of a hole scavenger (CPH). The prepared Au nanoparticles supported on TiO(2) showed strong photoabsorption at around 550 nm due to surface plasmon resonance (SPR) of Au and exhibited a photocatalytic activity in mineralization of formic acid in aqueous suspensions under irradiation of visible light (>ca. 520 nm). A linear correlation between photocatalytic activity and the amount of Au loaded, that is, the number of Au nanoparticles, was observed, indicating that the activity of Au/TiO(2) plasmonic photocatalysts can be controlled simply by the amount of Au loading using the CPH method and that the external surface area of Au nanoparticles is a decisive factor in mineralization of formic acid under visible light irradiation. Very high reaction rates were obtained in samples with 5 wt % Au or more, although the rate tended to be saturated. The CPH method can be widely applied for loading of Au nanoparticles on various TiO(2) supports without change in the original size independent of the TiO(2) phase. The rate of CO(2) formation also increased linearly with increase in the external surface area of Au. Interestingly, the TiO(2) supports showed different slopes of the plots. The slope is important for selection of TiO(2) as a material supporting colloidal Au nanoparticles.

We have synthesized metal-polymer hybrid colloidal particles characterized by an eccentric structure by precipitation polymerization in the presence of metal colloids. The key to the formation of an eccentric core-shell structure was to introduce metal colloids a few minutes after (rather than before) starting the polymerization. The hybrid particles were uniform in size, and each one of them contained only one metal nanoparticle at its surface after the experimental procedures had been optimized. This method could be extended to a number of different metal colloids stabilized by small molecules, and the yield was found to be more or less independent of the size of the metal nanoparticles. In addition, the position of the metal nanoparticle in the hybrid particle could be controlled by changing the concentration of cross-linker, and the overall size of the hybrid particles could be altered by solvent treatment. Because of the simplicity of this procedure, it should be possible to use it for the large-scale production of colloidal particles having a hybrid, complex structure.

Single-size platinum Pt6 subnanoclusters exhibit superior mass-specific and surface-specific activities for the oxygen reduction reaction.

Ptn subnanoclusters (n = 3–9) on a carbon substrate exhibit 1.6–2.2 times higher activity than the standard Pt/C catalysts. EXAFS experiments and DFT calculations show plausible structures and energetics for reaction intermediates in the processes.