Recently, Chinese scientists at Institute of solid State Physics (or ISSP), Hefei Institutes of Physical Science and University of Science and Technology of China (USTC) had successfully tuned the kernel of ~1nm bimetal particle.

They discovered an interesting phenomenon that the kernel alteration does not obviously change the absorption spectrum (including optical gap), but remarkably influences the electrochemical gap of the nanoparticle, indicating that the kernel tailoring does not comparably influence the optical and electrochemical gap of metal nanonanoparticles.

As we know, stable ultrasmall (less than 3 nm) metal nanoparticle is generally composed of inner pure metal kernel and outer metal-ligand-mixed staples, and the kernel is shielded by the outer staples.

Thus it is challenging to precisely add or remove the kernel atoms while the outer metal atoms remain the same, and such a kernel tuning was not achieved by any other research groups in the world.

Fortunately, by carefully selecting the protecting ligand with adequate steric hindrance, Chinese scientists at ISSP have successfully synthesized a novel nanocluster, in which the kernel can be regarded as that formed by the addition of two silver atoms to both ends of the Pt@Ag₁₂ icosohedral kernel of the Ag₂₄Pt(SR)₁₈ (SR: thiolate) nanocluster with the type and number of outer metal atoms remained, as revealed by single crystal X-ray crystallography (see Figure 1a).

Interestingly, compared with the previously reported Pt@Ag₁₂@Ag₁₂ structure, the novel alloy nanocluster exhibits a similar absorption (including the optical gap) but a different electrochemical gap (see Figure 1b), indicating that the kernel tuning does not necessarily alter both the optical and electrochemical gap.

"Such an inconsistence change between the electrochemical and optical gap of metal nanoclusters is not previously reported to the best of our knowledge, and one possible reason is the charge variation, which gets support from the computing conducted by YANG Jinlong’s group in USTC", said LIAO Lingwen, a researcher working with ISSP.

This work achieves for the first time a challenging kernel tuning and introduces a new strategy for nanocluster tuning, which provide novel insights into the structure and properties of metal nanoclusters and important implications for the structure property correlation of metal nanoclusters.

And the study is sponsored by NSFC, Key Program of 13th five-year plan, CASHIPS, and Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology.

Figure a. Schematic illustration of the Ag₂₆Pt and Ag₂₄Pt nanocluster structures. (Color scheme: green, platinum; red, light green and blue, silver; yellow, sulfur; pink, phosphorus; all carbon and hydrogen atoms are omitted for clarity). Figure b. UV-visible absorption spectra of Ag₂₆Pt and Ag₂₄Pt nanoclusters (a), and differential pulse voltammetry (DPV) spectra of Ag₂₆Pt (b) and Ag₂₄Pt (c). Figure c. The electron densities of the HOMO, HOMO-1 HOMO-2 and LUMO, LUMO+1 of the Ag₂₆Pt nanocluster (a-e) and the Ag₂₄Pt nanocluster (f-j). Figure d. X-ray structure of the Ag₂₆Pt nanocluster. (Color scheme: blue, platinum; red, silver; yellow, sulfur; pink, phosphorus; dark gray, carbon; white, hydrogen) (Image by HE Lizhong)