Synthesis of Au/Pt bimetallic nanoparticles with a Pt-rich shell and their high catalytic activities for aerobic glucose oxidation

Contemporary advances in photocatalytic CO2 reduction using single-atom catalysts supported on carbon-based materials

The persistent issue of CO2 emissions and their subsequent impact on the Earth's atmosphere can be effectively addressed through the utilization of efficient photocatalysts. Employing a sustainable carbon cycle via photocatalysis presents a promising technology for simultaneously managing the greenhouse effect and the energy dilemma. However, the efficiency of energy conversion encounters limitations due to inadequate carrier utilization and a deficiency of reactive sites. Single-atom catalysts (SACs) have demonstrated exceptional performance in efficiently addressing the aforementioned challenges. This review article commences with an overview of SAC types, structures, fundamentals, synthesis strategies, and characterizations, providing a logical foundation for the design and properties of SACs based on the correlation between their structure and efficiency. Additionally, we delve into the general mechanism and the role of SACs in photocatalytic CO2 reduction. Furthermore, we furnish a comprehensive survey of the latest advancements in SACs concerning their capacity to enhance efficiency, long-term stability, and selectivity in CO2 reduction. Carbon-structured support materials such as covalent organic frameworks (COFs), graphitic carbon nitride (g-C3N4), metal-organic frameworks (MOFs), covalent triazine frameworks (CTFs), and graphene-based photocatalysts have garnered significant attention due to their substantial surface area, superior conductivity, and chemical stability. These carbon-based materials are frequently chosen as support matrices for anchoring single metal atoms, thereby enhancing catalytic activity and selectivity. The motivation behind this review article lies in evaluating recent developments in photocatalytic CO2 reduction employing SACs supported on carbon substrates. In conclusion, we highlight critical issues associated with SACs, potential prospects in photocatalytic CO2 reduction, and existing challenges. This review article is dedicated to providing a comprehensive and organized compilation of recent research findings on carbon support materials for SACs in photocatalytic CO2 reduction, with a specific focus on materials that are environmentally friendly, readily accessible, cost-effective, and exceptionally efficient. This work offers a critical assessment and serves as a systematic reference for the development of SACs supported on MOFs, COFs, g-C3N4, graphene, and CTFs support materials to enhance photocatalytic CO2 conversion.

The role of the gold-platinum interface in AuPt/TiO2-catalyzed plasmon-induced reduction of CO2 with water

Bimetallic gold-platinum nanoparticles have been widely studied in the fields of nanoalloys, catalysis and plasmonics. Many preparation methods can lead to the formation of these bimetallic nanoparticles (NPs), and the structure and related properties of the nanoalloy often depend on the preparation method used. Here we investigate the ability of thermal dimethylformamide (DMF) reduction to prepare bimetallic gold-platinum sub-nm clusters supported on titania. We find that deposition of Pt preferentially occurs on gold. Formation of sub-nm clusters (vs. NPs) appears to be dependent on the metal concentration used: clusters can be obtained for metal loadings up to 4 wt% but 7-8 nm NPs are formed for metal loadings above 8 wt%, as shown using high resolution transmission electron microscopy (HRTEM). X-ray photoelectron spectroscopy (XPS) shows electron-rich Au and Pt components in a pure metallic form and significant platinum enrichment of the surface, which increases with increasing Pt/Au ratio and suggests the presence of Au@Pt core-shell type structures. By contrast, titania-supported bimetallic particles (typically >7 nm) obtained by sodium borohydride (NaBH₄) reduction in DMF, contain Au/Pt Janus-type objects in addition to oxidized forms of Pt as evidenced by HRTEM, which is in agreement with the lower Pt surface enrichment found by XPS. Both types of supported nanostructures contain a gold-platinum interface, as shown by the chemical interface damping, i.e. gold plasmon damping by Pt, found using UV-visible spectroscopy. Evaluation of the materials for plasmon-induced continuous flow CO₂ reduction with water, shows that: (1) subnanometer metallic clusters are not suitable for CO₂ reduction with water, producing hydrogen from the competing water reduction instead, thereby highlighting the plasmonic nature of the reaction; (2) the highest methane production rates are obtained for the highest Pt enrichments of the surface, i.e. the core-shell-like structures achieved by the thermal DMF reduction method; (3) selectivity towards CO₂ reduction vs. the competing water reduction is enhanced by loading of the plasmonic NPs, i.e. coverage of the titania semi-conductor by plasmonic NPs. Full selectivity is achieved for loadings above 6 wt%, regardless of the NPs composition and alloy structure.

Influence of electrochemical co-deposition of bimetallic Pt-Pd nanoclusters on polypyrrole modified ITO for enhanced oxidation of 4-(hydroxymethyl) pyridine

Bimetallic Pt–Pd nanoparticles were dispersed on polypyrrole coated indium-tin oxide coated polyethylene terephthalate sheets (ITO-PET sheets). The excellent filming property of pyrrole gives a high porous uniform active area for the proper adsorption of bimetallic transition metal nanoparticles. Electrochemical behavior of the modified electrodes was determined using cyclic voltammetry and impedance studies. The physicochemical properties of the modified electrodes were analyzed by scanning electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. To study the electrochemical oxidation of 4-(hydroxymethyl) pyridine in the presence of sodium nitrate in aqueous acidic medium, the modified electrode was used. It is evident from the study that the modified electrode shows better electrochemical activity towards the oxidation of 4-(hydroxymethyl) pyridine.

Bimetallic Pt–Pd nanoparticles were dispersed on polypyrrole coated indium–tin oxide coated polyethylene terephthalate sheets (ITO-PET sheets).

One-pot synthesis of Au-M@SiO2 (M = Rh, Pd, Ir, Pt) core-shell nanoparticles as highly efficient catalysts for the reduction of 4-nitrophenol

The conversion of p-nitrophenol (4-NP) to p-aminophenol (4-AP) is of great significance for pharmaceutical and material manufacturing. In this work, Au-M@SiO₂ (M = Rh, Pd, Ir, Pt) nanoparticles (NPs) with core-shell structures, which are expected to be excellent catalysts for the transformation of 4-NP to 4-AP, were synthesized by a facile one-pot one-step method. The structure and composition of the NPs were characterized through transmission electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy. Au-M@SiO₂ (M = Rh, Pd, Ir, Pt) core-shell NPs showed excellent catalytic activity in the reduction of 4-NP, which is superior to most catalysts reported in the previous literature. The enhanced catalytic activity of Au-M@SiO₂ core-shell NPs is presumably related to the bimetallic synergistic effect. This study provides a simple strategy to synthesize core-shell bimetallic NPs for catalytic applications.

Gold-Platinum Nanoparticles with Core-Shell Configuration as Efficient Oxidase-like Nanosensors for Glutathione Detection

Nanozymes, defined as nanomaterials that can mimic the catalytic activity of natural enzymes, have been widely used to develop analytical tools for biosensing. In this regard, the monitoring of glutathione (GSH), a key antioxidant biomolecule intervening in the regulation of the oxidative stress level of cells or related with Parkinson’s or mitochondrial diseases can be of great interest from the biomedical point of view. In this work, we have synthetized a gold-platinum Au@Pt nanoparticle with core-shell configuration exhibiting a remarkable oxidase-like mimicking activity towards the substrates 3,3′,5,5′-tetramethylbenzidine (TMB) and o-phenylenediamine (OPD). The presence of a thiol group (-SH) in the chemical structure of GSH can bind to the Au@Pt nanozyme surface to hamper the activation of O₂ and reducing its oxidase-like activity as a function of the concentration of GSH. Herein, we exploit the loss of activity to develop an analytical methodology able to detect and quantify GSH up to µM levels. The system composed by Au@Pt and TMB demonstrates a good linear range between 0.1–1.0 µM to detect GSH levels with a limit of detection (LoD) of 34 nM.

Study of Ultrasonic Attenuation and Thermal Conduction in Bimetallic Gold/Platinum Nanofluids : Effect of thermal conductivity on ultrasonic attenuation of gold and gold/platinum nanofluids

Here, we report the frequency dependent ultrasonic attenuation of monometallic gold and bimetallic gold/platinum based aqueous nanofluids (NFs). The as-synthesised bimetallic NFs (BMNFs) revealed less resistance to ultrasonic waves compared to the monometallic NFs. Thermal conductivity of both NFs taken at different concentrations revealed substantial conductivity improvement when compared to the base fluid, although gold/platinum showed lesser improvement compared to gold. Characterisation of the as-synthesised nanoparticles (NPs) and fluids was carried out with X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The distinct two-phase bimetallic nature of gold/platinum, its two plasmonic band optical absorption features and the spherical morphology of the particles were shown. The findings were correlated with the observed thermal and ultrasonic behaviour and proper rationalisation is provided. It was revealed that the comparatively lesser thermal conductivity of gold/platinum had direct implication on its attenuation property. The findings could have important repercussions in both industrial applications and in the mechanistic approach towards the field of ultrasonic attenuation in NFs.

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.

Advances in catalytic routes for the production of carboxylic acids from biomass: a step forward for sustainable polymers

Polymers are ubiquitously present in our daily life because they can meet a wide range of needs and fields of applications. This success, based on an irresponsible linear consumption of plastics and the access to cheap oil, is creating serious environmental problems. Two lines of actions are needed to cope with them: to adopt a circular consumption of plastics and to produce renewable carbon-neutral monomers. This review analyses the recent advances in the chemocatalytic processes for producing biomass-derived carboxylic acids. These renewable carboxylic acids are involved in the synthesis of relevant general purpose and specialty polyesters and polyamides; some of them are currently derived from oil, while others can become surrogates of petrochemical polymers due to their excellent performance properties. Polyesters and polyamides are very suitable to be depolymerised to other valuable chemicals or to their constituent monomers, what facilitates the circular reutilisation of these monomers. Different types of carboxylic acids have been included in this review: monocarboxylic acids (like glycolic, lactic, hydroxypropanoic, methyl vinyl glycolic, methyl-4-methoxy-2-hydroxybutanoic, 2,5-dihydroxypent-3-enoic, 2,5,6-trihydroxyhex-3-enoic acids, diphenolic, acrylic and δ-amino levulinic acids), dicarboxylic acids (2,5-furandicarboxylic, maleic, succinic, adipic and terephthalic acids) and sugar acids (like gluconic and glucaric acids). The review evaluates the technology status and the advantages and drawbacks of each route in terms of feedstock, reaction pathways, catalysts and economic and environmental evaluation. The prospects and the new research that should be undertaken to overcome the main problems threatening their economic viability or the weaknesses that prevent their commercial implementation have also been underlined.

Highly Correlated Size and Composition of Pt/Au Alloy Nanoparticles via Magnetron Sputtering onto Liquid

Pt/Au alloy nanoparticles (NPs) in a wide composition range have been synthesized by room-temperature simultaneous sputter deposition from two independent magnetron sources onto liquid PEG (MW = 600). The prepared NPs were alloyed with the face-centered cubic (fcc) structure. In addition, the particle sizes, composition, and shape are strongly correlated but can be tailored by an appropriate variation of the sputtering parameters. No individual particle but large agglomerates with partial alloy structure formed at Pt content of less than 16 atom %. Highly dispersed NPs with no agglomeration were observed in PEG when the quantity of Pt is more than 26 atom %. On the other hand, a small amount of Pt could terminate the agglomeration of Au when sputtering on the grids for transmission electron microscope observation. Our experiment and computer simulation carried out by two different methods indicate that the composition-dependent particle size of Pt/Au can be explained by the atomic concentration, formation energy of the cluster, and interaction between different metal atoms and the PEG molecule.

ISOBAM-stabilized Ni2+ colloidal catalysts: high catalytic activities for hydrogen generation from hydrolysis of KBH4

ISOBAM-104-stabilized Ni²⁺ colloidal catalysts were synthesized through a facile method and used for hydrogen generation from hydrolysis of potassium borohydride (KBH₄). Ni nanoparticles (NPs) were formed as the active phase during the catalytic process. Ultraviolet-visible spectrophotometry (UV-vis) and transmission electron microscopy were employed to characterize the structure and particle size of the as-formed Ni NPs. The results suggested that the catalytic activity of Ni²⁺ colloidal catalyst increased with the decreased size of as-formed Ni NPs, which is consistent with the results of density functional theory calculation. The highest catalytic activity of the catalyst can be 12400 ml-H₂ min^-1 g-Ni^-1, which was even higher than that of noble Pt or Pd colloidal catalysts prepared using identical methods and catalytic conditions. According to the Arrhenius method, the ISOBAM-104-stabilized Ni²⁺ colloidal catalysts showed low activation energies of about 41.3 kJ mol^-1 for the hydrogen generation from hydrolysis basic KBH₄ solution.

Oxidation of lignocellulosic platform molecules to value-added chemicals using heterogeneous catalytic technologies

This minireview gives an overview about heterogeneous catalytic technologies for the oxidation of key platform molecules (glucose, 5-hydroxymethylfurfural, furfural and levulinic acid) into valuable chemicals.

On the minimum reactant concentration required to prepare Au/M core-shell nanoparticles by the one-pot microemulsion route

The minimum reactant concentration required to synthesize Au/M (M = Ag, Pt, Pd, Ru …) core-shell nanoparticles by the one-pot microemulsion route was calculated by a simulation model under different synthesis conditions. This minimum concentration was proved to depend on the reduction potential of the slower metal M and on the rigidity of the surfactant film composing the microemulsion. Model results were tested by comparing with Au/M nanoparticles taken from literature. In all cases, experimental data obey model predictions. From this agreement, one can conclude that the smaller the standard potential of the slower reduction metal, the lower the minimum concentration needed to obtain core-shell nanoparticles. In addition, the higher the surfactant flexibility, the higher the minimum concentration to synthesize metal segregated nanoparticles. Model prediction allows to quantify which is the best value of concentration to prepare different pairs of core-shell Au/M nanoparticles in terms of nature of M metal in the couple and microemulsion composition. This outlook may become an advanced tool for fine-tuning Au/M nanostructures.

Graphical Abstract:

The Synergism of Platinum-Gold Bimetallic Nanoconjugates Enhances 5-Fluorouracil Delivery In Vitro

Nanoparticle application has significantly impacted the field of medicine. The need to develop novel drugs with higher therapeutic potential has stimulated the development of innovative delivery strategies to mitigate the potent side effects associated with known chemotherapeutic drugs. This paper describes the synthesis of platinum-gold bimetallic nanoparticles (PtAuBNps), their functionalisation with chitosan, and entrapment of the anticancer drug 5-fluorouracil (5-FU). All PtAuBNps and their drug nanocomposites were physico-chemically characterised, displaying desirable properties with regards to shape, size (<120 nm) and colloidal stability. 5-FU binding and loading capacities in PtAuBNps were found to be 90.17% and 22.56%, respectively. In vitro cytotoxicity profiles determined using the MTT and SRB assays reflected up to 65% cell death in the MCF-7, HepG2 and Caco-2 cell lines. These nanocomposites exhibited excellent physiochemical attributes, high specificity towards cancer cells, with a pH-sensitive drug release in a simulated acidic tumour microenvironment through zero-order release kinetics. In addition, they possessed the potential to traverse the mucosal lining facilitating oral drug administration. Overall, 5-FU encapsulation improved the bioavailability of the drug in cancer cells, with the promise of enhancing its therapeutic effect, biocompatibility and safety. These positive results highlight PtAuBNps as promising in vitro delivery systems and merits future in vivo research.

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).

Biosynthesis, characterization and leishmanicidal activity of a biocomposite containing AgNPs-PVP-glucantime

AIM

Development of functionalized nanocomposites containing AgNPs-PVP-Glucantime^® to evaluate their leishmanicidal activity as a novel method for improving the pharmacological properties of the drug Glucantime^® against extracellular promastigotes and intracellular amastigotes of Leishmania amazonensis in vitro to treat cutaneous leishmaniasis.

MATERIALS & METHODS

The silver nanoparticles and nanocomposites prepared containing silver nanoparticles, polyvinylpyrrolidone and different amounts of Glucantime were characterized using transmission electron microscopy, x-ray diffraction, energy-dispersive x-ray spectroscopy and ζ potential analysis; in addition, the in vitro cytotoxicity was evaluated.

RESULTS

The nanocomposites showed an inhibitory effect on the cellular viability of promastigote forms, with values of 47.06, 51.71 and 65.67% for nanocomposite₁, nanocomposite₂ and nanocomposite₃, respectively, as well as a dose-dependent decrease in the infectivity index, with values of 33.33 and 23% for nanocomposite₂ and nanocomposite₃, respectively.

CONCLUSION

The proposed nanocomposite reveals leishmanial activity and the absence of cytotoxicity in macrophages. Further investigations will be conducted in vivo.

Products of sugar beet processing as raw materials for chemicals and biodegradable polymers

This paper presents an overview of alternative uses for products of sugar beet processing, especially sucrose, as chemical raw materials for the production of biodegradable polymers. Traditionally, sucrose has not been considered as a chemical raw material, because of its use in the food industry and high sugar prices. Beet pulp and beetroot leaves have also not been considered as raw materials for chemical production processes until recently. However, current changes in the European sugar market could lead to falling demand and overproduction of sucrose. Increases in the production of white sugar will also increase the production of waste biomass, as a result of the processing of larger quantities of sugar beet. This creates an opportunity for the development of new chemical technologies based on the use of products of sugar beet processing as raw materials. Promising methods for producing functionalized materials include the acidic hydrolysis of sugars (sucrose, biomass polysaccharides), the catalytic dehydration of monosaccharides to HMF followed by catalytic oxidation of HMF to FDCA and polymerization to biodegradable polymers. The technologies reviewed in this article will be of interest both to industry and science.

This paper presents an overview of alternative uses for products of sugar beet processing, especially sucrose, as chemical raw materials for the production of biodegradable polymers.

Catalytic oxidation of carbohydrates into organic acids and furan chemicals

A review on the development of new routes for the production of organic acids and furan compoundsviacatalytic oxidation reactions.

An in vitro assessment of novel chitosan/bimetallic PtAu nanocomposites as delivery vehicles for doxorubicin

AIM

To synthesize and functionalize platinum (core)-gold (shell) bimetallic nanoparticles (PtAuBNps) with chitosan and doxorubicin to display favorable pharmacokinetics, biodegradability, biological activity and safety in vitro.

MATERIALS & METHODS

PtAuBNps and their drug nanocomposites were morphologically and physico-chemically characterized. Binding studies determined the efficiency and stability of the platform. In vitro release kinetics were evaluated under simulated environments, cytotoxicity profiles through MTT and Sulforodhamine B assays and apoptosis induction using the dual EtBr/AO staining.

RESULTS & DISCUSSION

The results obtained indicate that functionalized PtAuBNps displayed favorable physio-chemical attributes, high binding capabilities, pH-triggered drug release through zero-order release kinetics, cell-specific cytotoxicity and good colloidal stability.

CONCLUSION

The positive attributes of this novel delivery system bodes well for future in vivo studies.

Synergistic Effects in CNTs-PdAu/Pt Trimetallic Nanoparticles with High Electrocatalytic Activity and Stability

We present a straightforward physical approach for synthesizing multiwalled carbon nanotubes (CNTs)-PdAu/Pt trimetallic nanoparticles (NPs), which allows predesign and control of the metal compositional ratio by simply adjusting the sputtering targets and conditions. The small-sized CNTs-PdAu/Pt NPs (~3 nm, Pd/Au/Pt ratio of 3:1:2) act as nanocatalysts for the methanol oxidation reaction (MOR), showing excellent performance with electrocatalytic peak current of 4.4 A mgPt -1 and high stability over 7000 s. The electrocatalytic activity and stability of the PdAu/Pt trimetallic NPs are much superior to those of the corresponding Pd/Pt and Au/Pt bimetallic NPs, as well as a commercial Pt/C catalyst. Systematic investigation of the microscopic, crystalline, and electronic structure of the PdAu/Pt NPs reveals alloying and charge redistribution in the PdAu/Pt NPs, which are responsible for the promotion of the electrocatalytic performance.

Insight into growth of Au-Pt bimetallic nanoparticles: an in situ XAS study

Au-Pt bimetallic nanoparticles have been synthesized through a one-pot synthesis route from their respective chloride precursors using block copolymer as a stabilizer. Growth of the nanoparticles has been studied by simultaneous in situ measurement of X-ray absorption spectroscopy (XAS) and UV-Vis spectroscopy at the energy-dispersive EXAFS beamline (BL-08) at Indus-2 SRS at RRCAT, Indore, India. In situ XAS spectra, comprising both X-ray near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) parts, have been measured simultaneously at the Au and Pt L₃-edges. While the XANES spectra of the precursors provide real-time information on the reduction process, the EXAFS spectra reveal the structure of the clusters formed in the intermediate stages of growth. This insight into the formation process throws light on how the difference in the reduction potential of the two precursors could be used to obtain the core-shell-type configuration of a bimetallic alloy in a one-pot synthesis method. The core-shell-type structure of the nanoparticles has also been confirmed by ex situ energy-dispersive spectroscopy line-scan and X-ray photoelectron spectroscopy measurements with in situ ion etching on fully formed nanoparticles.

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

Understanding of the “structure-activity” relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au³⁺ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size.

Noble metal-based bimetallic nanoparticles: the effect of the structure on the optical, catalytic and photocatalytic properties

Nanoparticles composed of two different metal elements show novel electronic, optical, catalytic or photocatalytic properties from monometallic nanoparticles. Bimetallic nanoparticles could show not only the combination of the properties related to the presence of two individual metals, but also new properties due to a synergy between two metals. The structure of bimetallic nanoparticles can be oriented in random alloy, alloy with an intermetallic compound, cluster-in-cluster or core-shell structures and is strictly dependent on the relative strengths of metal-metal bond, surface energies of bulk elements, relative atomic sizes, preparation method and conditions, etc. In this review, selected properties, such as structure, optical, catalytic and photocatalytic of noble metals-based bimetallic nanoparticles, are discussed together with preparation routes. The effects of preparation method conditions as well as metal properties on the final structure of bimetallic nanoparticles (from alloy to core-shell structure) are followed. The role of bimetallic nanoparticles in heterogeneous catalysis and photocatalysis are discussed. Furthermore, structure and optical characteristics of bimetallic nanoparticles are described in relation to the some features of monometallic NPs. Such a complex approach allows to systematize knowledge and to identify the future direction of research.

Nanostructured copper/copper oxide hybrids: combined experimental and theoretical studies

The inhomogeneous distribution of Al and Cu atoms in sintered precursors makes the released Cu atoms susceptible to oxidation during dealloying.

Understanding the Metal Distribution in Core-Shell Nanoparticles Prepared in Micellar Media

The factors that govern the reaction rate of Au/Pt bimetallic nanoparticles prepared in microemulsions by a one-pot method are examined in the light of a simulation model. Kinetic analysis proves that the intermicellar exchange has a strong effect on the reaction rates of the metal precursors. Relating to Au, reaction rate is controlled by the intermicellar exchange rate whenever concentration is high enough. With respect to Pt, the combination of a slower reduction rate and the confinement of the reactants inside micelles gives rise to an increase of local Pt salt concentration. Two main consequences must be emphasized: On one hand, Pt reduction may continue independently whether or not a new intermicellar exchange takes place. On the other hand, the accumulation of Pt reactants accelerates the reaction. As the reactant accumulation is larger when the exchange rate is faster, the resulting Pt rate increases. This results in a minor difference in the reduction rate of both metals. This difference is reflected in the metal distribution of the bimetallic nanoparticle, which shows a greater degree of mixture as the intermicellar exchange rate is faster.

Cage-like effect in Au-Pt nanoparticle synthesis in microemulsions: a simulation study

The different distributions of metals in bimetallic nanoparticles synthesized in microemulsions were studied by computer simulation. The simulations demonstrated that if the difference between the reduction potentials of both metals is about 0.15-0.3 V, the compartmentalization of the reaction media causes the accumulation of slower reduction reactants in the microemulsions droplets, which favours the chemical reaction like a cage effect: increasing the local concentration of the slower reduction metal salt gives rise to a faster reduction, so the differences in reduction rates of both metals are attenuated. A more coincidental reduction of both metals deeply affects the nanoparticle structure, causing a better mixed alloy. This effect will be more pronounced when the concentration is higher and the intermicellar exchange rate is faster. This means that for any fixed microemulsion the nanoparticle structure can be modified by changing the reactant concentration: the core can be enriched in the faster reduction metal by lower concentrations, and the shell can be enriched in the slower metal by higher concentrations. Based on these observations, this study suggests a route to help experimentalists better create nanoparticles with a pre-defined structure.

Synthesis of Ni/Au/Co trimetallic nanoparticles and their catalytic activity for hydrogen generation from alkaline sodium borohydride aqueous solution

Alloyed Ni/Au/Co nanoparticles with negatively-charged Au, Co atoms, and positively-charged Ni atoms were prepared as effective catalysts for hydrolysis of NaBH₄.

A robust site-specific Au@SiO2@AgPt nanorod/nanodots superstructure for in situ SERS monitoring of catalytic reactions

A site-specific trimetallic Au@SiO₂@AgPt nanorod/nanodots superstructure can be fabricated to provide real-time SERS monitoring of catalytic reactions.

Food safety control of zeranol through voltammetric immunosensing on Au–Pt bimetallic nanoparticle surfaces

This study reports an accurate and sensitive strategy for zeranol (ZER) determination in bovine urine samples.

Heterogeneous Metal Catalysts for Oxidation Reactions

Oxidation reactions may be considered as the heart of chemical synthesis. However, the indiscriminate uses of harsh and corrosive chemicals in this endeavor are threating to the ecosystems, public health, and terrestrial, aquatic, and aerial flora and fauna. Heterogeneous catalysts with various supports are brought to the spotlight because of their excellent capabilities to accelerate the rate of chemical reactions with low cost. They also minimize the use of chemicals in industries and thus are friendly and green to the environment. However, heterogeneous oxidation catalysis are not comprehensively presented in literature. In this short review, we clearly depicted the current state of catalytic oxidation reactions in chemical industries with specific emphasis on heterogeneous catalysts. We outlined here both the synthesis and applications of important oxidation catalysts. We believe it would serve as a reference guide for the selection of oxidation catalysts for both industries and academics.

Pt-Cu bimetallic alloy nanoparticles supported on anatase TiO2: highly active catalysts for aerobic oxidation driven by visible light

Visible light irradiation (λ > 450 nm) of Pt-Cu bimetallic alloy nanoparticles (~3-5 nm) supported on anatase TiO2 efficiently promotes aerobic oxidation. This is facilicated via the interband excitation of Pt atoms by visible light followed by the transfer of activated electrons to the anatase conduction band. The positive charges formed on the nanoparticles oxidize substrates, and the conduction band electrons reduce molecular oxygen, promoting photocatalytic cycles. The apparent quantum yield for the reaction on the Pt-Cu alloy catalyst is ~17% under irradiation of 550 nm monochromatic light, which is much higher than that obtained on the monometallic Pt catalyst (~7%). Cu alloying with Pt decreases the work function of nanoparticles and decreases the height of the Schottky barrier created at the nanoparticle/anatase heterojunction. This promotes efficient electron transfer from the photoactivated nanoparticles to anatase, resulting in enhanced photocatalytic activity. The Pt-Cu alloy catalyst is successfully activated by sunlight and enables efficient and selective aerobic oxidation of alcohols at ambient temperature.