Shuangxi Xing

A systems approach towards the stoichiometry-controlled hetero-assembly of nanoparticles

A central theme in nanotechnology is to advance the fundamental understanding of nanoscale component assembly, thereby allowing rational structural design that may lead to materials with novel properties and functions. Nanoparticles (NPs) are often regarded as artificial atoms, but their reactions are not readily controllable. Here, we demonstrate a complete nanoreaction system whereby colloidal NPs are rationally assembled and purified. Two types of functionalized gold NPs (A and B) are bonded to give specific products AB, AB(2), AB(3) and AB(4). The stoichiometry control is realized by fine-tuning the charge repulsion among the B-NPs. The products are protected by a polymer, which allows their isolation in high purity. The integration of hetero-assembly, stoichiometry control, protection scheme and separation method may provide a scalable way to fabricate sophisticated nanostructures.

Reducing the symmetry of bimetallic Au@Ag nanoparticles by exploiting eccentric polymer shells.

We demonstrate a facile colloidal method for synthesizing Janus nanoparticles, whose eccentric polymer shells are exploited to fabricate eccentric bimetallic cores.

Highly controlled core/shell structures: tunable conductive polymer shells on gold nanoparticles and nanochains

Controls in coating gold nanoparticles with conductive polymers are reported, where uniform core/shell nanoparticles with tailored core aggregation and shell thickness are unambiguously demonstrated. In the presence of sodium dodecylsulfate (SDS), the adsorption and in situpolymerization of aniline or pyrrole on the surface of gold nanoparticles gives uniform polymer shells. A typical single encapsulation of 10 nm gold nanoparticles gave ∼99.1% monomers out of 1074 particles surveyed. The shell growth was found to be kinetically controlled; polyaniline was successively grown on 22 nm gold nanoparticles by multiple growth cycles, giving shell thicknesses of 14, 31, 61 and 92 nm, respectively. We show that the aggregation of gold nanoparticles can be controllably promoted in this system, by simply timing SDS addition, to give linearly aggregated cores of 2–20 particles. The in situ formation of conductive polymer shells has allowed the isolation and unambiguous characterization of these nanochains for the first time. The one-step, “mix-and-wait” synthesis solely utilizes inexpensive starting materials and is, therefore, well-suited for fabrication of large quantities of core/shell nanoparticles. The core/shell nanoparticles form stable colloidal suspensions and can be readily purified by centrifugation.

Fabrication of Polymer Nanocavities with Tailored Openings

A templated fabrication of open nanocavities is reported, where rational control of partial polymer attachment on sacrificial metal cores introduces openings in the polymer shells. This approach provides a facile means to modify the structural features of polymer nanocavities by manipulating the surface chemistry of colloidal nanoparticles. In particular, the anisotropic geometry of gold nanorods is exploited to promote the anisotropic polymer attachment, such that two diametric openings occurred in the polymer shell. After etching the gold nanorods, this approach yields open nanochannels that are tunable in both diameter and length. The synthetic scope of the anisotropic core/shell nanoparticles is expanded, supporting the previously proposed mechanism. We demonstrate that reducing the symmetry of nano-objects could open up new ways to create structural features using simple assembly and etching techniques. The thermostability of the open polymer nanostructures is also investigated.

Nickel foam based polypyrrole–Ag composite film: a new route toward stable electrodes for supercapacitors

Polypyrrole (PPy)–Ag composites have been directly deposited on a nickel foam via the redox reaction between pyrrole and silver nitrate. As a catalyst, the nickel foam was able to accelerate the redox reaction and lead to the formation of PPy–Ag composites, which shows a strong adhesive force to the substrate. The electrochemical properties of the PPy–Ag–nickel foam electrode were systematically investigated by using cyclic voltammetry, galvanostatic charge–discharge and cycle stability measurements in 0.5 M K2SO4 electrolyte. The redox performance properties, good charge–discharge stability and high specific capacitance of 493 F g−1 at a current density of 1 A g−1 demonstrated the appropriate application of the PPy–Ag–nickel foam electrode for the high energy density supercapacitors.

Triple-layer (au@perylene)@polyaniline nanocomposite: unconventional growth of faceted organic nanocrystals on polycrystalline Au.

Unconventional crystal growth: core/shell nanocrystals were obtained by growth of a dominant single-crystalline phase of perylene over polycrystalline Au nanoparticle seeds and isolated by coating with polyaniline (PANI) shells. Perylene is released in the presence of sodium dodecyl sulfate (SDS) micelles. The TEM images show (Au@perylene)@PANI nanocomposites before and after complete release of perylene leaving Au@PANI (inset).

Measuring the unusually slow ionic diffusion in polyaniline via study of yolk-shell nanostructures.

We demonstrate a unique capability in partially oxidizing the oligoaniline shell on gold nanoparticles to polyaniline. Because of the solubility difference, the unreacted inner shell section can be selectively dissolved by 2-propanol, giving yolk-shell nanostructures and, thus, making it possible for assessing the oxidized section. The ionic diffusion through the polymer shell is found to be the rate-determining step in the overall process. Conservative estimates show that the diffusion coefficient of AuCl(4)(-) is at least 700 times slower than that of the typical rate values in traditional studies. It is most likely caused by the lack of micropores in the polymer structures. Such mircopores are hard to avoid in preparing polymer membranes by casting or drying of polymers dissolved in organic solvents. We can rule out the presence of irregular pores on the basis of the uniformly oxidized shell section. With the nanoscale shells, the system is sensitive enough to detect minute changes in the shell or small differences among the individual nanoparticles. Even with a small increase in porosity, for example, when the polyaniline shell is swollen using small amounts of DMF (3%, 5%, or 10% in aqueous solutions), the diffusion coefficient of AuCl(4)(-) increases to 4, 11, and 17 times, respectively. Thus, our study demonstrates a new methodology for studying the diffusion of ions in hydrophobic polymers.

Facile synthesis of hollow urchin-like gold nanoparticles and their catalytic activity

The galvanic replacement reaction between Ag nanoparticles (NPs) and HAuCl4 followed by addition of ascorbic acid led to the formation of AuNPs sharing both urchin-like and hollow structures. The AgNPs took as sacrificial templates to guide the hollow structure and the intermediates provided rough surface and active sites for the further deposition of AuNPs, which originated from the reduction of excess HAuCl4 by ascorbic acid. These unique structured AuNPs presented excellent optical properties and great advantages in catalysis applications.

In situ assembly of monodispersed Ag nanoparticles in the channels of ordered mesopolymers as a highly active and reusable hydrogenation catalyst

In this study, we report a simple in situ auto-reduction strategy for the fabrication of Ag@FDU-15 nanocomposites, in which the small sized Ag nanoparticles are monodispersed in the channels of FDU-15 ordered mesopolymers. The as-prepared Ag@FDU-15 nanocomposites were characterized by small and wide angle X-ray diffraction (XRD), nitrogen sorption, thermo-gravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). TEM results show that the silver nanoparticles are uniformly dispersed with a mean diameter of 5.6 ± 0.5 nm. When used as a hydrogenation catalyst, the Ag@FDU-15 nanocomposites exhibit excellent catalytic performance and reusability for the reduction of 4-nitrophenol (4-NP) in the presence of NaBH4.

One-step synthesis of composite vesicles: Direct polymerization and in situ over-oxidation of thiophene

Composite vesicles with embedded Au nanoparticles are directly prepared from thiophene and Au nanoparticles in aqueous solution in the presence of H2O2 and a catalytic amount of FeCl3. The number, shape, and structure of the vesicles thereof can be readily controlled. We provide evidence that these vesicles contain an aqueous phase in their cavities. The direct synthesis offers an economical route to nanoscale containers and also a rare example for the minimal conditions of vesicle formation.