Bimetallic Janus Nanocrystals: Syntheses and Applications

Abstract

compounds, core-shell, core-satellite (or core-frame), and Janus nanocrystals. [2,10] Figure 1 shows schematic illustrations of these four structures at an atomic level. Both alloys and intermetallic compounds are formed when two metals are homogeneously mixed at the atomic level. [10] While alloys feature a random distribution of atoms in space, intermetallic compounds take a highly ordered structure with the atoms of each metal precisely positioned at specific sites. The atomic fractions of the two metals are typically limited by a well-defined stoichiometry in intermetallic compounds. When the two metals are spatially segregated, they will form core-shell, -satellite, and -frame structures, as well as bimetallic Janus nanocrystal. [2] Although the metals in all these structures are separated by a heterogeneous interface, bimetallic Janus nanocrystals are particularly interesting for their simplicity associated with a side-by-side, asymmetric arrangement. This interface also supports the charge separation between two metals with different work functions and inner electron transfer, offering a means to maneuver their electronic structures and thus bestowing superior catalytic and photocatalytic capabilities upon the Janus nanocrystals. [11][12][13] Furthermore, the plasmonic coupling associated with the side-by-side elemental distribution of a Janus nanocrystal offers unique optical properties (e.g., bonding and antibonding plasmon modes, as well as Fano resonance profiles) for various applications. [9,[14][15][16][17] The past few decades have witnessed tremendous advances in the colloidal synthesis of metal nanocrystals with well-controlled compositions, sizes, shapes, and structures. [1,2,18] However, the fabrication of bimetallic Janus nanocrystals has been hindered by the difficulties in achieving a side-by-side distribution of two different metals in a single particle. [19] In many cases, alloying may take place during the synthesis, especially when the two metals share similar atomic radii, crystal lattice constants, valencies, and electronegativities. [1] Besides, the nucleation and growth of a different metal from a preformed seed often proceed in a symmetric pattern for the generation of core-satellite, -frame, and -shell structures rather than a Janus structure with reduced symmetry. [19][20][21] To this end, synthetic strategies capable of disrupting the symmetric growth while preventing the formation of alloys are critical to the successful preparation of bimetallic Janus nanocrystals. A good example can be found in the synthesis of Pd-Ag or Pd-Au Janus nanocrystals, in which the asymmetric growth of Ag on preformed Pd cubic seeds could be induced and maintained by manipulating the reduction kinetics. [22][23][24][25] This Review presents recent progress related to the syntheses, properties, and applications of bimetallic Janus nanocrystals.Bimetallic Janus nanocrystals have received considerable interest in recent years owing to their unique properties and niche applications. The sideby-side distri...

Patchy metal nanoparticles with polymers: controllable growth and two-way self-assembly

“…3d-f and S15 †), can be grown on pAuNP-14 seeds. 44 The examples of Ag and Pt domains selectively grown from the exposed Au surface have a yield of >95% and reasonable uniformity. The energy-dispersive X-ray spectroscopy (EDX) mapping and high-angle annular dark-field (HAADF) images confirm the formation of asymmetric coating (Fig.…”

“…This presumably is attributed to the fast deposition rate where the weak ligands allow the fast binding and diffusion of adatoms. 44 We measured the UV-vis spectra of pAuNPs grown with different second capping ligands at Au eq = 6. The LSPR peaks of pAuNPs for CTAC, PVP and PAA capped pAuNPs are around 540 nm (Fig.…”

Mass-determining role in the electrophoretic separation of colloidal plasmonic nanoparticle oligomers

“…Hetero-structured plasmonic dimers have been widely applied in many fields, such as photocatalysis, 23,52 sensing, 53,54 photothermal 55 and so on. 56 While the direct electrophoretic separation of these hetero-structured plasmonic dimers with high purity remains a great challenge, 57 with a deep understanding of the mass-determining role in electrophoretic separation, this challenge should be overcome by rationally designing building blocks with an appropriate mass difference. For instance, as the mass of nanoparticles can be tuned by their density, gold nanospheres and Au/Ag core-shell cubes with rationally designed mass differences were employed to construct spherical-cubic hetero-structured plasmonic dimers.…”

Seed surface doping-mediated seeded growth of Au–Ag Janus nanoparticles with tunable sizes and multiple plasmonic absorption modes

“…The Janus configuration also breaks the intrinsic face-centered cubic (fcc) lattice symmetry, thus favoring a complex absorption feature. 4 The case of Au-Ag bimetallic nanocrystals is taken as an example for a detailed analysis. Despite the tremendous progress achieved in the synthesis of Janus bimetallic nanocrystals in recent reports, it is still technically challenging to produce Au-Ag Janus nanocrystals.…”

“…The Janus configuration also breaks the intrinsic face-centered cubic ( fcc ) lattice symmetry, thus favoring a complex absorption feature. 4…”