Growth pathways of exotic Cu@Au core@shell structures: the key role of misfit strain

The CuAu system is characterized by a large lattice mismatch which causes a misfit strain in its core@shell architectures. Here we simulate the formation of Cu@Au core@shell nanoparticles by Au deposition on a preformed seed, and we study the effect of the shape and composition of the starting seed on the growth pathway. Three geometric shapes of the starting seed are considered: truncated octahedra, decahedra and icosahedra. For each shape, we consider two compositions, pure Cu and CuAu, at equicomposition and intermixed chemical ordering. Our results show that the shape and composition of the seed have significant effects on the growth pathways of Cu@Au core@shell nanoparticles. When starting with icosahedral seeds, the growing structure stays in that motif always. When starting with truncated octahedral and decahedral seeds, we have observed that there is a clear difference between the pure and intermixed seeds. For pure seeds, the growth often leads to exotic structures that are obtained after some structural transformations. For mixed seeds, the growth leads to quite regular structures resembling those obtained for pure metals. These growth pathways originate from strain relaxation mechanisms, which are rationalized by calculating the atomic level stress.

Seeded Growth of Gold-Copper Janus Nanostructures as a Tandem Catalyst for Efficient Electroreduction of CO2 to C2+ Products

Gold-copper (Au-Cu) Janus nanostructures (Au-Cu Janus NSs) are successfully prepared using N-oleyl-1,3-propanediamine as capping agent and Cu(acac)₂ as the precursor in a typical seeded growth strategy. By preferably depositing Cu atoms on one side of concave cubic Au seeds, the Cu part gradually grows larger as more Cu precursors are added, making the size tuning feasible in the range of 74-156 nm. When employed as an electrocatalyst for electrochemical CO₂ reduction (CO₂ RR), the Au-Cu Janus NSs display superior performance to Au@Cu core-shell NSs and Cu NPs in terms of C₂₊ products selectivity (67%) and C₂₊ partial current density (-0.29 A cm^-2 ). Combined experimental verification and theoretical simulations reveal that CO spillover from Au sites to the nearby Cu counterparts would enhance CO coverage and thus promote C-C coupling, highlighting the unique structural advantages of the Au-Cu Janus NSs toward deep reduction of CO₂ . The current work provides a facile strategy to fabricate tandem catalyst with a Janus structure and validates its structural advantages toward CO₂ RR, which are of critical importance for the rational design of efficient CO₂ RR catalyst.

Au-Cu@PANI Alloy Core Shells for Aerobic Fibrin Degradation under Visible Light Exposure

Fibrin plays a critical role in wound healing and hemostasis, yet it is also the main case of cardiovascular diseases and thrombosis. Here, we show the unique design of Au-Cu@PANI alloy core-shell rods for fibrin clot degradation. Microscopic (transmission electron microscopy (TEM), scanning transmission electron microscopy-energy-dispersive X-ray (STEM-EDX)) and structural characterizations (powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS)) of the Au-Cu@PANI hybrid material reveal the formation of Au-Cu heterogeneous alloy core rods (aspect ratio = 3.7) with thin Cu₂O and PANI shells that create a positive surface charge (ζ-potential = +22 mV). This architecture is supported by the survey XPS spectrum showing the presence of Cu 2p, N 1s, and C 1s features with binding energies of 934.8, 399.7, and 284.8 eV, respectively. Upon photolysis (λ ≥ 495 or 590 nm), these hybrid composite nanorods provide sufficient excited-state redox potential to generate reactive oxygen species (ROS) for degradation of model fibrin clots within 5-7 h. Detailed scanning electron microscopy (SEM) analysis of the fibrin network shows significant morphology modification including formation of large voids and strand termini, indicating degradation of fibrin protofibril by Au-Cu@PANI. The dye 1,3-diphenylisobenzofuran (DPBF) used to detect the presence of ¹O₂ shows a 27% bleaching of the absorption at λ = 418 nm within 75 min of irradiation of an aqueous Au-Cu@PANI solution in air. Moreover, electron paramagnetic resonance (EPR) spin-trapping experiments reveal a hyperfine-coupled triplet signature at room temperature with intensities 1:1:1: and g-value = 2.0057, characteristic of the reaction between the spin probe 4-Oxo-TEMP and ¹O₂ during irradiation. Controlled ¹O₂ scavenging experiments by NaN₃ show 82% reduction in the spin-trapped EPR signal area. Both DPBF bleaching and EPR spin trapping indicate that in situ generated ¹O₂ is responsible for fibrin strand scission. This unique nanomaterial function via use of ubiquitous oxygen as a reagent could open creative avenues for future in vivo biomedical applications to treat fibrin clot diseases.

Direct Micromolding of Bimetals and Transparent Conducting Oxide Using Metal-TOABr Complexes as Single-Source Precursors

Patterning of metals, alloys, and conducting oxides is vitally important for many industrial applications pertaining to many technological devices. In this report, we have used the metal anion alkyl ammonium complex (M-TOABr) as a single-source precursor to obtain thin films as well as micro (μ)-patterns of bimetals (Au-Pd, Au-Pt, Au-Cu, and Pt-Pd) and conducting oxides (ITO). This complex can be easily filled inside the soft mold and converted to the desired material in a single step known as direct patterning. The as-obtained μ-pattern comprises a well-connected network of nanocrystals giving rise to metallic conductivity. These periodically aligned bimetals and transparent conducting oxide (TCO) microwires could effectively serve as electrodes as well as an electrocatalyst with the prudence of providing passage for light transmission for many functional photoelectrochemical devices. In addition, the electrochemical stability of the bimetallic film was examined by fabricating a supercapacitor device and by studying its performance.

One-pot preparation of nanoporous Ag-Cu@Ag core-shell alloy with enhanced oxidative stability and robust antibacterial activity

Metallic core–shell nanostructures have inspired prominent research interests due to their better performances in catalytic, optical, electric, and magnetic applications as well as the less cost of noble metal than monometallic nanostructures, but limited by the complicated and expensive synthesis approaches. Development of one-pot and inexpensive method for metallic core–shell nanostructures’ synthesis is therefore of great significance. A novel Cu network supported nanoporous Ag-Cu alloy with an Ag shell and an Ag-Cu core was successfully synthesized by one-pot chemical dealloying of Zr-Cu-Ag-Al-O amorphous/crystalline composite, which provides a new way to prepare metallic core–shell nanostructures by a simple method. The prepared nanoporous Ag-Cu@Ag core-shell alloy demonstrates excellent air-stability at room temperature and enhanced oxidative stability even compared with other reported Cu@Ag core-shell micro-particles. In addition, the nanoporous Ag-Cu@Ag core-shell alloy also possesses robust antibacterial activity against E. Coli DH5α. The simple and low-cost synthesis method as well as the excellent oxidative stability promises the nanoporous Ag-Cu@Ag core-shell alloy potentially wide applications.

Engineering the Composition and Structure of Bimetallic Au-Cu Alloy Nanoparticles in Carbon Nanofibers: Self-Supported Electrode Materials for Electrocatalytic Water Splitting

The bimetallic Au-Cu alloy nanoparticles have been constructed in electrospun carbon nanofibers (Au-Cu/CNFs), employing as high efficient hydrogen evolution reaction (HER) electrode. The morphology, structure, and composition of bimetallic Au-Cu alloy can be controlled by adjusting the precursor nanofibers through a facile approach. With the increased Cu content, the Au-Cu alloy have a transition from the homogeneous AuCu₃ alloy phase to the Au₃Cu phase with Cu shell. The self-supported bimetallic Au-Cu/CNFs hybrid can be directly employed as electrode materials for water splitting, and it showed excellent electrochemical activity, including long-term stability, high exchange current density, and low overpotential. The outstanding HER performance could be mainly attributed to the synergistic interactions and interfacial effects of Au-Cu alloy with high densities of uncoordinated surface atoms. In addition, the fast charge transport and the fast kinetic for the desorption of the gas were originated from the self-supported three-dimensional architectures consist of integrated Au-Cu/CNFs networks. The Au-Cu/CNFs with mass ratio of 1:2 (Au₃Cu-Cu "core-shell" alloy) obtain the lowest overpotential of 83 mV (at j = 10 mA cm^-2), lowest Tafel slope of 70 mV dec^-1, and highest exchange current density of 0.790 mA cm^-2. The present investigations offer a new strategy for the design and synthesis of unique nanocrystals in energy conversion related application.

Facile synthesis and heteroepitaxial growth mechanism of Au@Cu core–shell bimetallic nanocubes probed by first-principles studies

This work provided a facile strategy for the synthesis of Au@Cu core–shell nanostructures. The proposed growth mechanism was probed by a first-principles investigation.

Synthesis of biocompatible Au-ZnTe core-shell nanoparticles

A novel, solution-based route to biocompatible, cysteine-capped gold-zinc telluride (Au-ZnTe) core-shell nanoparticles with potential in biomedical applications is described. The optical properties of the core-shell nanoparticles show combined beneficial features of the individual parent components. The tunable emission properties of the semiconductor shell render the system useful for imaging and biological labeling applications. Powder X-ray diffraction analysis reveals the particles contain crystalline Au and ZnTe. Transmission electron microscope (TEM) imaging of the particles indicates they are largely spherical with sizes in the order of 2-10 nm. Elemental mapping using X-ray energy dispersive spectroscopy (XEDS) in the scanning transmission electron microscope (STEM) mode supports a core-shell morphology. The biocompatibility and cytotoxicity of the core-shells was investigated on a human pancreas adenocarcinoma (PL45) cell line using the WST-1 cell viability assay. The results showed that the core-shells had no adverse effects on the PL45 cellular proliferation or morphology. TEM imaging of PL45 cell cross sections confirmed the cellular uptake and isolation of the core-shell nanoparticles within the cytoplasm via membrane interactions. The fluorescence properties of the Au-ZnTe core-shell structures within the PL45 cell lines results confirmed their bio-imaging potential. The importance and novelty of this research lies in the combination of gold and zinc telluride used to produce a water soluble, biocompatible nanomaterial which may be exploited for drug delivery applications within the domain of oncology.

Formation of Rh frame nanorods using Au nanorods as sacrificial templates

Formation of Rh frame nanorods was studied using Au nanorods having high-index facets as sacrificial templates.