Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters

Complete miscibility of immiscible elements at the nanometre scale

Understanding the mixing behaviour of elements in a multielement material is important to control its structure and property. When the size of a multielement material is decreased to the nanoscale, the miscibility of elements in the nanomaterial often changes from its bulk counterpart. However, there is a lack of comprehensive and quantitative experimental insight into this process. Here we explored how the miscibility of Au and Rh evolves in nanoparticles of sizes varying from 4 to 1 nm and composition changing from 15% Au to 85% Au. We found that the two immiscible elements exhibit a phase-separation-to-alloy transition in nanoparticles with decreased size and become completely miscible in sub-2 nm particles across the entire compositional range. Quantitative electron microscopy analysis and theoretical calculations were used to show that the observed immiscibility-to-miscibility transition is dictated by particle size, composition and possible surface adsorbates present under the synthesis conditions.

Molecular dynamics study on the thermodynamic stability and structural evolution of crown-jewel structured PdCu nanoalloys

The novel crown-jewel (CJ) structured PdCu nanoalloys have attracted considerable interest in high-performance single-atom catalysis. The characteristics of demanding high-temperature calcination in the synthesis of these samples disable us from experimentally understanding the details of the thermal evolution behavior of PdCu nanoclusters during the heating process. In this work, by analyses of potential energy surface, bond order parameter, and radial distribution function, we have theoretically studied the thermodynamic stabilities and structural evolution of Pd-decorated Cu-based CJ nanoclusters with various compositions and sizes by molecular dynamics simulations. PdCu nanoclusters undergo a cuboctahedral (Cubo) to icosahedral (Ico) structural transformation before melting. This transformation is size- and Pd-composition dependent. The small size and high Pd-composition of PdCu nanoclusters facilitate this transformation. In addition, we find that the surface and interface effects of clusters have an important impact on the structural transformation and Cubo-Ico structural transformation is strongly related to the release of excess energy.

Excellent Catalytic Performance of ISOBAM Stabilized Co/Fe Colloidal Catalysts toward KBH4 Hydrolysis

Recently, developing a cost-effective and high-performance catalyst is regarded as an urgent priority for hydrogen generation technology. In this work, ISOBAM-104 stabilized Co/Fe colloidal catalysts were prepared via a co-reduction method and used for the hydrogen generation from KBH₄ hydrolysis. The obtained ISOBAM-104 stabilized Co₁₀Fe₉₀ colloidal catalysts exhibit an outstanding catalytic activity of 37,900 mL-H₂ min^-1 g-Co^-1, which is far higher than that of Fe or Co monometallic nanoparticles (MNPs). The apparent activation energy (E_a) of the as-prepared Co₁₀Fe₉₀ colloidal catalysts is only 14.6 ± 0.7 kJ mol^-1, which is much lower than that of previous reported noble metal-based catalysts. The X-ray photoelectron spectroscopy results and density functional theory calculations demonstrate that the electron transfer between Fe and Co atoms is beneficial for the catalytic hydrolysis of KBH₄.

The Factors Dictating Properties of Atomically Precise Metal Nanocluster Electrocatalysts

Metal nanoparticles occupy an important position in electrocatalysis. Unfortunately, by using conventional synthetic methodology, it is a great challenge to realize the monodisperse composition/structure of metal nanoparticles at the atomic level, and to establish correlations between the catalytic properties and the structure of individual catalyst particles. For the study of well-defined nanocatalysts, great advances have been made for the successful synthesis of nanoparticles with atomic precision, notably ligand-passivated metal nanoclusters. Such well-defined metal nanoclusters have become a type of model catalyst and have shown great potential in catalysis research. In this review, the authors summarize the advances in the utilization of atomically precise metal nanoclusters for electrocatalysis. In particular, the factors (e.g., size, metal doping/alloying, ligand engineering, support materials as well as charge state of clusters) affecting selectivity and activity of catalysts are highlighted. The authors aim to provide insightful guidelines for the rational design of electrocatalysts with high performance and perspectives on potential challenges and opportunities in this emerging field.

Au/Pt-Egg-in-Nest Nanomotor for Glucose-Powered Catalytic Motion and Enhanced Molecular Transport to Living Cells

Nanostructures converting chemical energy to mechanical work by using benign metabolic fuels, have huge implications in biomedical science. Here, we introduce Au/Pt-based Janus nanostructures, resembling to "egg-in-nest" morphology (Au/Pt-ENs), showing enhanced motion as a result of dual enzyme-relay-like catalytic cascade in physiological biomedia, and in turn showing molecular-laden transport to living cells. We developed dynamic-casting approach using silica yolk-shell nanoreactors: first, to install a large Au-seed fixing the silica-yolk aside while providing the anisotropically confined concave hollow nanospace to grow curved Pt-dendritic networks. Owing to the intimately interfaced Au and Pt catalytic sites integrated in a unique anisotropic nest-like morphology, Au/Pt-ENs exhibited high diffusion rates and displacements as the result of glucose-converted oxygen concentration gradient. High diffusiophoresis in cell culture media increased the nanomotor-membrane interaction events, in turn facilitated the cell internalization. In addition, the porous network of Au/Pt-ENs facilitated the drug-molecule cargo loading and delivery to the living cells.

Developments of the Electroactive Materials for Non-Enzymatic Glucose Sensing and Their Mechanisms

A comprehensive review of the electroactive materials for non-enzymatic glucose sensing and sensing devices has been performed in this work. A general introduction for glucose sensing, a facile electrochemical technique for glucose detection, and explanations of fundamental mechanisms for the electro-oxidation of glucose via the electrochemical technique are conducted. The glucose sensing materials are classified into five major systems: (1) mono-metallic materials, (2) bi-metallic materials, (3) metallic-oxide compounds, (4) metallic-hydroxide materials, and (5) metal-metal derivatives. The performances of various systems within this decade have been compared and explained in terms of sensitivity, linear regime, the limit of detection (LOD), and detection potentials. Some promising materials and practicable methodologies for the further developments of glucose sensors have been proposed. Firstly, the atomic deposition of alloys is expected to enhance the selectivity, which is considered to be lacking in non-enzymatic glucose sensing. Secondly, by using the modification of the hydrophilicity of the metallic-oxides, a promoted current response from the electro-oxidation of glucose is expected. Lastly, by taking the advantage of the redistribution phenomenon of the oxide particles, the usage of the noble metals is foreseen to be reduced.

Spectroscopically clean Au nanoparticles for catalytic decomposition of hydrogen peroxide

Au nanoparticles synthesized from colloidal techniques have the capability in many applications such as catalysis and sensing. Au nanoparticles function as both catalyst and highly sensitive SERS probe can be employed for sustainable and green catalytic process. However, capping ligands that are necessary to stabilize nanoparticles during synthesis are negative for catalytic activity. In this work, a simple effective mild thermal treatment to remove capping ligands meanwhile preserving the high SERS sensitivity of Au nanoparticles is reported. We show that under the optimal treatment conditions (250 °C for 2 h), 50 nm Au nanoparticles surfaces are free from any capping molecules. The catalytic activity of treated Au nanoparticles is studied through H₂O₂ decomposition, which proves that the treatment is favorable for catalytic performance improvement. A reaction intermediate during H₂O₂ decomposition is observed and identified.

Ag(I)-Thiolate-Protected Silver Nanoclusters for Solar Cells: Electrochemical and Spectroscopic Look into the Photoelectrode/Electrolyte Interface

Intrinsic low stability and short excited lifetimes associated with Ag nanoclusters (NCs) are major hurdles that have prevented the full utilization of the many advantages of Ag NCs over their longtime contender, Au NCs, in light energy conversion systems. In this report, we diagnosed the problems of conventional thiolated Ag NCs used for solar cell applications and developed a new synthesis route to form aggregation-induced emission (AIE)-type Ag NCs that can significantly overcome these limitations. A series of Ag(0)/Ag(I)-thiolate core/shell-structured NCs with different core sizes were explored for photoelectrodes, and the nature of the two important interfacial events occurring in Ag NC-sensitized solar cells (photoinduced electron transfer and charge recombination) were unveiled by in-depth spectroscopic and electrochemical analyses. This work reveals that the subtle interplay between the light absorbing capability, charge separation dynamics, and charge recombination kinetics in the photoelectrode dictates the solar cell performance. In addition, we demonstrate significant improvement in the photocurrent stability and light conversion efficiency that have not been achieved previously. Our comprehensive understanding of the critical parameters that limit the light conversion efficiency lays a foundation on which new principles for designing Ag NCs for efficient light energy conversion can be built.

Advances in porous and nanoscale catalysts for viable biomass conversion

Solid catalysts with unique porosity and nanoscale properties play a promising role for efficient valorization of biomass into sustainable advanced fuels and chemicals.

High-Power Abiotic Direct Glucose Fuel Cell Using a Gold-Platinum Bimetallic Anode Catalyst

We developed a high-power abiotic direct glucose fuel cell system using a Au-Pt bimetallic anode catalyst. The high power generation (95.7 mW cm^-2) was attained by optimizing operating conditions such as the composition of a bimetallic anode catalyst, loading amount of the metal catalyst on a carbon support, ionomer/carbon weight ratio when the catalyst was applied to the anode, glucose and KOH concentrations in the fuel solution, and operating temperature and flow rate of the fuel solution. It was found that poly(N-vinyl-2-pyrrolidone)-stabilized Au₈₀Pt₂₀ nanoparticles (mean diameter 1.5 nm) on a carbon (Ketjen Black 600) support function as a highly active anode catalyst for the glucose electrooxidation. The ionomer/carbon weight ratio also greatly affects the cell properties, which was found to be optimal at 0.2. As for the glucose concentration, a maximum cell power was derived at 0.4-0.6 mol dm^-3. A high KOH concentration (4.0 mol dm^-3) was preferable for deriving the maximum power. The cell power increased with the increasing flow rate of the glucose solution up to 50 cm³ min^-1 and leveled off thereafter. At the optimal condition, the maximum power density and corresponding cell voltage of 58.2 mW cm^-2 (0.36 V) and 95.7 mW cm^-2 (0.34 V) were recorded at 298 and 328 K, respectively.

Polyethyleneimine capped bimetallic Au/Pt nanoclusters are a viable fluorescent probe for specific recognition of chlortetracycline among other tetracycline antibiotics

A highly selective method has been developed for the fluorometric determination of chlortetracycline (CTC) among other tetracycline antibiotics (TCs). It is making use of fluorescent Au/Pt nanoclusters (NCs) capped with polyethyleneimine (Au/PtNCs@PEI). The nanoprobe, with a green emission peaking at 512 nm, was synthesized by an environmentally friendly hydrothermal method. The capped NCs have a large Stokes shift (∼150 nm), are insensitive to extreme pH values and high ionic strength, and are excellently photostable under UV irradiation. In the presence of CTC, the fluorescence of the capped NCs is quenched due to aggregation. The effect is also found for tetracycline, oxytetracycline and doxycycline. This shows that sensitive but non-selective detection of such TCs is possible. However, CTC is specifically complexed by Al(III) ions, and this generates a strong fluorescence peaking at 520 nm even though the fluorescence of the capped NCs is fully quenched. Obviously, the effects are caused by CTC only, and this enables CTC to be specifically recognized by an "on-off-on" strategy. Fluorescence increases linearly in the 0.5 to 10 μM CTC concentration range, and the limit of detection is 0.35 μM. The method was successfully applied to the determination of CTC in (spiked) milk, and the recoveries suggest that this fluorescent probe is an effective tool for detecting CTC in foodstuff. Graphical abstract Schematic illustration and photographic images of the luminescence quenching response of Au/Pt nanoclusters (Au/PtNCs) toward chlortetracycline (CTC) (from on to off), and then the recovery upon Al³⁺ addition (from off to on).

Phase transition in crown-jewel structured Au-Ir nanoalloys with different shapes: a molecular dynamics study

We have studied the melting process for crown-jewel structured Ir₅₅, Ir₅₄Au, Ir₄₃Au₁₂, Ir₂₅Au₃₀, Ir₁₃Au₄₂, and Au₅₅ nanoclusters in the icosahedral, Ir₅₅, Ir₅₄Au, Ir₄₃Au₁₂, Ir₁₉Au₃₆, Ir₁₃Au₄₂, and Au₅₅ nanoclusters in the cuboctahedral, and Ir₅₄, Ir₅₃Au, Ir₄₇Au₇, Ir₁₇Au₃₇, Ir₇Au₄₇, and Au₅₄ nanoclusters in the decahedral morphologies. We have investigated the different thermodynamic, structural, and dynamical properties for the different nanoclusters in the different structures. Our thermodynamic results indicated that as the concentration of Au atoms in the nanoclusters increases, the absolute value of internal energy, and so the melting points, of the nanoclusters decrease. It is also shown that the Au atoms decrease the melting temperature of the pure cuboctahedral cluster more than that of the other structures. We have also found that the Au atoms were located in favorable positions at the surface sites of nanoalloys. Also, the doping of the Ir nanocluster by Au atoms makes the cluster more stable. It is also found that nanoclusters with different morphologies have almost the same stability. Our structural results indicated that after the melting process, the Au atoms generally tend to lie in the outer shell of the cluster, but the Ir atoms generally tend to lie in the core of the cluster (see the Ir₁₃Au₄₂ and Ir₇Au₄₇ nanoclusters, for example). We have also found the interesting result that the Ir₇Au₄₇ nanocluster shows a solid-solid transition from a decahedral structure to an icosahedral structure before melting. The Ir₄₃Au₁₂ nanocluster also shows a transformation from a cuboctahedral structure to an icosahedral-like structure before melting. Our dynamical results showed that doping of the Ir₅₅ cluster with an Au atom sharply increases the self-diffusion coefficient in the initial state in the solid phase, especially in icosahedral and cuboctahedral structures. It is also shown that the Ir₁₃Au₄₂ cluster in icosahedral and cuboctahedral and the Ir₇Au₄₇ and Ir₁₇Au₃₇ clusters in decahedral morphologies have smaller values of self-diffusion coefficients than other clusters after the melting point and that this could be due to the formation of core-shell structures.

Palladium nanoparticles entrapped in a self-supporting nanoporous gold wire as sensitive dopamine biosensor

Traced dopamine (DA) detection is critical for the early diagnosis and prevention of some diseases such as Parkinson's, Alzheimer and schizophrenia. In this research, a novel self-supporting three dimensional (3D) bicontinuous nanoporous electrochemical biosensor was developed for the detection of dopamine by Differential Pulse Voltammetry (DPV). This biosensor was fabricated by electrodepositing palladium nanoparticles (Pd) onto self-supporting nanoporous gold (NPG) wire. Because of the synergistic effects of the excellent catalytic activity of Pd and novel structure of NPG wire, the palladium nanoparticles decorated NPG (Pd/NPG) biosensor possess tremendous superiority in the detection of DA. The Pd/NPG wire biosensor exhibited high sensitivity of 1.19 μA μΜ-1, broad detection range of 1-220 μM and low detection limit up to 1 μM. Besides, the proposed dopamine biosensor possessed good stability, reproducibility, reusability and selectivity. The response currents of detection in the fetal bovine serum were also close to the standard solutions. Therefore the Pd/NPG wire biosensor is promising to been used in clinic.

Pt-Bi decorated nanoporous gold for high performance direct glucose fuel cell

Binary PtBi decorated nanoporous gold (NPG-PtBi) electrocatalyst is specially designed and prepared for the anode in direct glucose fuel cells (DGFCs). By using electroless and electrochemical plating methods, a dense Pt layer and scattered Bi particles are sequentially coated on NPG. A simple DGFC with NPG-PtBi as anode and commercial Pt/C as cathode is constructed and operated to study the effect of operating temperatures and concentrations of glucose and NaOH. With an anode noble metal loading of only 0.45 mg cm^-2 (Au 0.3 mg and Pt 0.15 mg), an open circuit voltage (OCV) of 0.9 V is obtained with a maximum power density of 8 mW cm^-2. Furthermore, the maximum gravimetric power density of NPG-PtBi is 18 mW mg^-1, about 4.5 times higher than that of commercial Pt/C.