Surfactant-Directed Fabrication of Supercrystals from the Assembly of Polyhedral Au–Pd Core–Shell Nanocrystals and Their Electrical and Optical Properties

Abstract

Au-Pd core-shell nanocrystals with cubic, truncated cubic, cuboctahedral, truncated octahedral, and octahedral structures have been employed to form micrometer-sized polyhedral supercrystals by both the droplet evaporation method and novel surfactant diffusion methods. Observation of cross-sectional samples indicates shape preservation of interior nanocrystals within a supercrystal. Low-angle X-ray diffraction techniques and electron microscopy have been used to confirm the presence of surfactant between contacting nanocrystals. By diluting the nanocrystal concentration or increasing the solution temperature, supercrystal size can be tuned gradually to well below 1 μm using the surfactant diffusion method. Rectangular supercrystal microbars were obtained by increasing the amounts of cubic nanocrystals and surfactant used. Au-Ag core-shell cubes and PbS cubes with sizes of 30-40 nm have also been fabricated into supercrystals, showing the generality of the surfactant diffusion approach to form supercrystals with diverse composition. Electrical conductivity measurements on single Au-Pd supercrystals reveal loss of metallic conductivity due to the presence of insulating surfactant. Cubic Au-Pd supercrystals show infrared absorption at 3.2 μm due to extensive plasmon coupling. Mie-type resonances centered at 9.8 μm for the Au-Pd supercrystals disappear once the Pd shells are converted into PdH after hydrogen absorption.

Surfactant‐directed Pd‐nanoparticle assemblies as efficient nanoreactors for water remediation

“…In this process, the driving force mainly comes from the effect brought about by the PdNP assembly in minimizing the electrostatic repulsion between the head groups of the surfactants. 15 The wellordered architectures directed by the surfactant assembly are presumed to be preserved during the reduction of Pd precursors, as already shown. 2 The presence of the PdNPs in the assemblies are clearly observed in the HRTEM image shown in Figure 2F, in which the inset evidences a distance of 0.231 nm between the two nearest atom rows, as expected for the (111) lattice spacing of face-centered cubic Pd crystals.…”

“…[1][2][3][6][7][8] Their performance and stability, however, are often compromised by aggregation phenomena, and therefore, devising new strategies suitable to avoid these problems is a priority research area. 4,5,[8][9][10][11][12][13][14][15] High-molecular-weight organic compounds like surfactants, polymers, and metal-organic frameworks can be used as soft templates to obtain size-and shape-controlled nanomaterials. 4,5,[12][13][14] Self-assembly of surfactants provides a particularly useful way to prepare well-ordered and ultrafine nanomaterials.…”

“…4,5,[12][13][14] Self-assembly of surfactants provides a particularly useful way to prepare well-ordered and ultrafine nanomaterials. 2,5,12,15 Because of their functional groups and ionic properties, surfactants provide useful sorption sites for metal precursors, may induce particles assembly, and generally lead to the formation of highly dispersed and stable metal NPs. [16][17][18] In addition to stabilizing the metal NPs, the surfactant ligands may induce specific physicochemical properties to the NPs, 8,19 thereby influencing the nanomaterials' solubility and catalytic properties.…”

Ligand Versatility in Supercrystal Formation

“…Both the droplet evaporation method and the surfactant diffusion technique were successfully employed by Chiu et al for the assembly of Au‐Pd core‐shell NPs into SCs. Again, the NP shape was observed to strongly influence the morphology of the SCs.…”

Seed‐Mediated Growth of Silver Nanocubes in Aqueous Solution with Tunable Size and Their Conversion to Au Nanocages with Efficient Photothermal Property

“…Considering the great potential of using polyhedrals ilver nanocrystals such as cubes and octahedra for catalysis, surfaceenhanced Raman scattering (SERS) detection of molecular species, plasmonics, and supercrystalf ormation through particle assembly,i ti sh ighly desirable to advance synthetic approaches for making these particles. [1][2][3][4][5][6][7][8][9] Major previous efforts to grow silver nanocubes and other polyhedral structures involve the use of ap olyol process at 150-180 8C, in which ethylene glycol, diethylene glycol,o r1 ,5-pentanediolw ere used as the solvent, and poly(vinylpyrrolidone) (PVP) polymer served as the capping agent and am ild reducing agent. [10][11][12][13][14] Formation of Ag nanocubes and plates has also been demonstrated by heatingasolution mixture of AgNO 3 , N,N-dimethylformamide (DMF) and PVP at 180 8C.…”