Fig. 1. Synthesis of metal and alloy nanoparticles by ultrasound-assisted dealloying of Mg-Cu/Ni (Ag, Au, Pt, Pd)-Gd metallic glass ribbons. (a) Typical synthetic procedure to prepare metal and alloy nanoparticles by ultrasound-assisted dealloying metallic glass ribbons. (b-f) Photographs of as-prepared colloidal Cu (after standing for 5 h), Ag (after standing for 2 h), Cu-Pt (after standing for 24 h), Cu-Au (after standing for 24 h), and Cu-Au-Pt-Pd (after standing for 24 h) nanoparticles, respectively. (g-h) Photographs of colloidal Au (after standing for 10 days) and Au-Pt-Pd-Cu (after standing for 10 days) nanoparticles prepared by further dealloying of colloidal Cu-Au and Cu-Au-Pt-Pd nanoparticles, respectively.

Fig. 2. TEM images and size distributions of metal nanoparticles. (a1-g1, a2-g2) Representative low-magnification TEM images and high-magnification TEM images of Cu (a1, a2), Ag (b1, b2), Cu-Pt (c1, c2), Cu-Au (d1, d2), Cu-Au-Pt-Pd (e1, e2), Au (f1, f2), and Au-Pt-Pd-Cu (g1, g2) nanoparticles. (a3-g3) Size distribution histograms of Cu (a3), Ag (b3), Cu-Pt (c3), Cu-Au (d3), Cu-Au-Pt-Pd (e3), Au (f3), and Au-Pt-Pd-Cu (g3) nanoparticles.

Fig. 3. XRD spectra and elemental maps. (a) XRD spectra of the as-synthesized Cu, Ag, Au, Cu-Pt, Cu-Au, Cu-Au-Pt-Pd, and Au-Pt-Pd-Cu nanoparticles. The blue, brown, pink, and red vertical lines represent the reference peaks of pure Au, Pt, Ag, and Cu, respectively. (b-c) TEM and scanning TEM (STEM) images of typical Au-Pt-Pd-Cu nanoparticles, respectively. (d-g) STEM-EDS elemental maps of the Au (d), Pt (e), Pd (f), and Cu (g) in typical Au-Pt-Pd-Cu nanoparticles.

Fig. 4. Evolution of the intermediate products by ultrasound-assisted dealloying Mg61Cu28Gd11 metallic glass precursor ribbons. (a, b) SEM images of the outer surface (a) and cross section (b) of a metallic glass ribbon after dealloying for 2 min. (c-f) SEM images of the intermediate products after dealloying for 2 min (c, d) and 5 min (e, f). (g, h) TEM images of the intermediate products after dealloying for 20 min (g) and 45 min (h). (i) Differential scanning calorimetry (DSC) curves of the Mg-Cu/Ni (Ag, Au, Pt, Pd)-Gd metallic glasses. (j) XRD spectra of the intermediate products after dealloying for 2 min, 5 min, 20 min, 45 min, and 90 min. Due to the atmospheric oxidation during the preparation and test processes, a small amount of Cu2O can be detected in the samples. (k) Mean diameter of metal and alloy nanoparticles vs. corresponding mean diameter of ligaments in nanoporous metals by dealloying Mg-Cu/Ni(Ag, Au, Pt, Pd)-Gd metallic glasses without UT. The inserts show SEM images of the corresponding nanoporous Cu and Cu-Au.

Fig. 5. Schematic illustration of the formation mechanism of Cu nanoparticles. (a) Metallic glass precursor ribbons. (b) Remaining metallic glass precursor ribbon and partly dealloyed intermediate fragments that were peeled off from the outer layers of the corresponding remaining metallic glass ribbons. The red regions represent the supercooled liquid regions (Tg < T < Tx) induced by the local glass transition. (c) Dealloying and breakage of intermediate fragments into small nanoporous Cu-rich particles. (d) Dealloying and breakage of small nanoporous Cu-rich particles into Cu-rich ligament debris. (e) Dealloying and breakage of Cu-rich ligament debris into short Cu nanorods and Cu nanoparticles. (f) Spheroidization of Cu nanoparticles.