Search Results (60)

Well-defined supported metal nanoparticle catalysts, with high uniformity in particle sizes of the dispersed metal, are crucial for studying their catalyzed reactions that exhibit structure sensitivity. For such catalysts, conventional methods of preparation may prove unsuitable in controlling the nanoparticle size and distribution. In this work, the systematic growth of supported Pd and Pt particles was achieved through the method of electroless deposition (ED), in which additional metal was deposited on preexisting particles of the same metal. The ED process was investigated by varying the pump time, pump speed, and molar ratios of the reagents during the continuous addition of the metal precursor, as well as the reducing agent and stabilizer, which were hydrazine and ethylenediamine, respectively. This allowed for the precise control of deposition rates, thus regulating the supported metal particle size, size distribution, and particle density. A slower deposition rate was achieved by increasing the amount of the ethylenediamine stabilizer and lowering the pumping speed. Slower rates of deposition resulted in smaller particle sizes and tighter size distributions compared to other preparations with the same metal weight loading, as characterized via X-ray diffraction (XRD), chemisorption, and scanning-transmission electron microscopy (STEM) methods. Full article

In this study, we investigate the electrodeposition of various metals on silicon. Mn, Co, Ni, Ru, Pd, Rh, and Pt were identified as promising candidates for controlled electrodeposition onto silicon. Electrochemical evaluations employing cyclic voltammetry, Scanning Electron Microscopy (SEM) associated with energy-dispersive X-Ray Spectroscopy (SEM-EDS), and X-Ray Photoelectron Spectroscopy (XPS) techniques confirmed the deposition of Pd, Rh, and Pt as nanoparticles. Multi-cycle charge-controlled depositions were subsequently performed to evaluate the possibility of achieving tunable electrodeposition of nanostructured rhodium on n-doped silicon. The procedure increased surface coverage from 9% to 84%, with the average particle size diameter ranging from 57 nm to 168 nm, and with an equivalent thickness of the deposits up to 43.9 nm, varying the number of charge-controlled deposition cycles. The electrodeposition of rhodium on silicon presents numerous opportunities across various scientific and technological domains, driving innovation and enhancing the performance of devices and materials used in catalysis, electronics, solar cells, fuel cells, and sensing. Full article

Efficient and low-cost nanocatalysts are extremely desirable for the catalytic reduction of 4-nitrophenol (4-NP). A smaller nanocatalyst particle size and stronger support effect can significantly enhance the catalytic performance. Naturally occurring halloysite nanotubes (HNTs) are promising alternative supports for fine metal nanoparticles, but the smooth surface and single type of functional groups on HNTs are usually unfavorable for the anchoring of metal ions. Herein, we modified HNTs using a mild and controllable molten salt etching method to create a rough surface (rHNTs), followed by loading Pt–Ni alloys to prepare Pt–Ni/rHNTs for the catalytic reduction of 4-NP. The results demonstrate that ultrafine Pt–Ni alloy nanoparticles with a diameter of 1.60 nm are uniformly dispersed on the rough surface of rHNTs. The particle size and catalytic performance can be tuned by adjusting the loading amount of Pt–Ni. The optimized Pt–Ni/rHNT (1 wt %) nanocatalyst reveals the smallest Pt–Ni particle size and the highest catalytic rate of 0.1953 min⁻¹, which exceeds many Pt–Ni-based catalysts in previous reports. This work offers an ingenious idea for the mild surface modification of HNTs and a brilliant perspective for the rational design of inexpensive 4-NP reduction nanocatalysts. Full article

The growing demand for hydrogen–air fuel cells with a proton-exchange membrane has increased interest in the development of scalable technologies for the synthesis of Pt/C catalysts that will allow us to fine-tune the microstructure of such materials. We have developed a new in situ technique for controlling the kinetics of the transformation of a platinum precursor into its nanoparticles and deposited Pt/C catalysts, which might be applicable during the liquid-phase synthesis in concentrated solutions and carbon suspensions. The technique is based on the analysis of changes in the redox potential and the reaction medium coloring during the synthesis. The application of the developed technique under conditions of scaled production has made it possible to obtain Pt/C catalysts with 20% and 40% platinum loading, containing ultra-small metal nanoparticles with a narrow size distribution. The electrochemically active surface area of platinum and the mass activity of synthesized catalysts in the oxygen electroreduction reaction have proved to be significantly higher than those of commonly used commercial analogs. At the same time, despite the small size of nanoparticles, the catalysts’ degradation rate turned out to be the same as that of commercial analogs. Full article

Self-doped CuS nanoparticles (NPs) were successfully synthesized via microwave-assisted polyol process to act as co-catalysts to TiO₂ nanofiber (NF)-based photoanodes to achieve higher photocurrents on visible light-assisted water electrolysis. The strategy adopted to perform the copper cation sulfidation in polyol allowed us to overcome the challenges associated with the copper cation reactivity and particle size control. The impregnation of the CuS NPs on TiO₂ NFs synthesized via hydrothermal corrosion of a metallic Ti support resulted in composites with increased visible and near-infrared light absorption compared to the pristine support. This allows an improved overall efficiency of water oxidation (and consequently hydrogen generation at the Pt counter electrode) in passive electrolyte (pH = 7) even at 0 V bias. These low-cost and easy-to-achieve composite materials represent a promising alternative to those involving highly toxic co-catalysts. Full article

Ultrasmall nanoparticles (diameter 2 nm) of silver, platinum, and bimetallic nanoparticles (molar ratio of Ag:Pt 0:100; 20:80; 50:50; 70:30; 100:0), stabilized by the thiolated ligand glutathione, were prepared and characterized by transmission electron microscopy, differential centrifugal sedimentation, X-ray photoelectron spectroscopy, small-angle X-ray scattering, X-ray powder diffraction, and NMR spectroscopy in aqueous dispersion. Gold nanoparticles of the same size were prepared as control. The particles were fluorescently labeled by conjugation of the dye AlexaFluor-647 via copper-catalyzed azide-alkyne cycloaddition after converting amine groups of glutathione into azide groups. All nanoparticles were well taken up by HeLa cells. The cytotoxicity was assessed with an MTT test on HeLa cells and minimal inhibitory concentration (MIC) tests on the bacteria Escherichia coli and Staphylococcus xylosus. Notably, bimetallic AgPt nanoparticles had a higher cytotoxicity against cells and bacteria than monometallic silver nanoparticles or a physical mixture of silver and platinum nanoparticles. However, the measured release of silver ions from monometallic and bimetallic silver nanoparticles in water was very low despite the ultrasmall size and the associated high specific surface area. This is probably due to the surface protection by a dense layer of thiolated ligand glutathione. Thus, the enhanced cytotoxicity of bimetallic AgPt nanoparticles is caused by the biological environment in cell culture media, together with a polarization of silver by platinum. Full article

Weak doping can broaden, shift, and quench plasmon peaks in nanoparticles, but the mechanistic intricacies of the diverse responses to doping remain unclear. In this study, we used the time-dependent density functional theory (TD-DFT) to compute the excitation properties of transition-metal Pd- or Pt-doped gold and silver atomic arrays and investigate the evolution characteristics and response mechanisms of their plasmon peaks. The results demonstrated that the Pd or Pt doping of the off-centered 10 × 2 atomic arrays broadened or shifted the plasmon peaks to varying degrees. In particular, for Pd-doped 10 × 2 Au atomic arrays, the broadened plasmon peak significantly blueshifted, whereas a slight red shift was observed for Pt-doped arrays. For the 10 × 2 Ag atomic arrays, Pd doping caused almost no shift in the plasmon peak, whereas Pt doping caused a substantial red shift in the broadened plasmon peak. The analysis revealed that the diversity in these doping responses was related to the energy positions of the d electrons in the gold and silver atomic clusters and the positions of the doping atomic orbitals in the energy bands. The introduction of doping atoms altered the symmetry and gap size of the occupied and unoccupied orbitals, so multiple modes of single-particle transitions were involved in the excitation. An electron transfer analysis indicated a close correlation between excitation energy and the electron transfer of doping atoms. Finally, the differences in the symmetrically centered 11 × 2 doped atomic array were discussed using electron transfer analysis to validate the reliability of this analytical method. These findings elucidate the microscopic mechanisms of the evolution of plasmon peaks in doped atomic clusters and provide new insights into the rational control and application of plasmons in low-dimensional nanostructures. Full article

Bimetallic nanomaterials have generated significant interest across diverse scientific disciplines, due to their unique and tunable properties arising from the synergistic combination of two distinct metallic elements. This study presents a novel approach for synthesizing branched gold–platinum nanoparticles by utilizing poly(allylamine hydrochloride) (PAH)-stabilized branched gold nanoparticles, with a localized surface plasmon resonance (LSPR) response of around 1000 nm, as a template for platinum deposition. This approach allows precise control over nanoparticle size, the LSPR band, and the branching degree at an ambient temperature, without the need for high temperatures or organic solvents. The resulting AuPt branched nanoparticles not only demonstrate optical activity but also enhanced catalytic properties. To evaluate their catalytic potential, we compared the enzymatic capabilities of gold and gold–platinum nanoparticles by examining their peroxidase-like activity in the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). Our findings revealed that the incorporation of platinum onto the gold surface substantially enhanced the catalytic efficiency, highlighting the potential of these bimetallic nanoparticles in catalytic applications. Full article

Monodisperse Pt nanoparticles supported on carbon (Pt/C) were prepared via an impregnation method. By changing the concentration of the platinum precursor in the initial reagent mixture, the average particle size (d) could be controlled to within a narrow range of less than 2 nm. The specific activity (SA) of these materials, when applied to the oxygen reduction reaction (ORR), increased rapidly with d in the range below 1.8 nm, with a maximum SA at d = 1.3 nm. This value is approximately four times that of a commercial Pt/CB catalyst. The electrochemical active area, ECAA (electrochemical surface area (ECSA)/specific surface area (SSA) × 100), decreased drastically from 100% with decreases in d below 1.3 nm. In this study, we present a correlation between SA and ECAA as a means of determining the appropriate d for polymer electrolyte fuel cells (PEFCs) and propose an optimal size. Full article

Porous metallic nanomaterials exhibit interesting physical and chemical properties, and are widely used in various fields. Traditional fabrication techniques are limited to metallurgy, sintering, electrodeposition, etc., which limit the control of pore size and distribution, and make it difficult to achieve materials with high surface areas. On the other hand, the chemical preparation of metallic nanoparticles is usually carried out with strong reducing agents or at high temperature, resulting in the formation of dispersed particles which cannot evolve into porous metal. In this study, we reported the simple fabrication of coral-like mesoporous Pd nanomaterial (Pd NC) with a ligament size of 4.1 nm. The fabrication was carried out by simple solvothermal reduction at a mild temperature of 135 °C, without using any templates. The control experiments suggested that tetrabutylammonium bromide (TBAB) played a critical role in the Pd(II) reduction into Pd nanoclusters and their subsequent aggregation to form Pd NC, and another key point for the formation of Pd NC is not to use a strong reducing agent. In alkaline water electrolysis, the Pd NC outperforms the monodisperse Pd NPs and the state-of-the-art Pt (under large potentials) for H₂ evolution reaction, probably due to its mesoporous structure and large surface area. This work reports a simple and novel method for producing porous metallic nanomaterials with a high utilization efficiency of metal atoms, and it is expected to contribute to the practical preparation of porous metallic nanomaterials by solvothermal reductions. Full article

Surfactants are widely used in the synthesis of nanoparticles, as they have a remarkable ability to direct their growth to obtain well-defined shapes and sizes. However, their post-synthesis removal is a challenge, and the methods used often result in morphological changes that defeat the purpose of the initial controlled growth. Moreover, after the removal of surfactants, the highly active surfaces of nanomaterials may undergo structural reconstruction by exposure to a different environment. Thus, ex situ characterization after air exposure may not reflect the effect of the cleaning methods. Here, combining X-ray photoelectron spectroscopy, in situ infrared reflection absorption spectroscopy, and environmental transmission electron microscopy measurements with CO probe experiments, we investigated different surfactant-removal methods to produce clean metallic Pt nanoparticles from surfactant-encapsulated ones. It was demonstrated that both ultraviolet-ozone (UV-ozone) treatment and room temperature O₂ plasma treatment led to the formation of Pt oxides on the surface after the removal of the surfactant. On the other hand, when H₂ was used for plasma treatment, both the Pt⁰ oxidation state and nanoparticle size distribution were preserved. In addition, H₂ plasma treatment can reduce Pt oxides after O₂-based treatments, resulting in metallic nanoparticles with clean surfaces. These findings provide a better understanding of the various options for surfactant removal from metal nanoparticles and point toward non-thermal plasmas as the best route if the integrity of the nanoparticle needs to be preserved. Full article

Due to the depletion of fossil fuels, the demand for renewable energy has increased, thus stimulating the development of novel materials for energy conversion devices such as fuel cells. In this work, nickel nanoparticles loaded on reduced graphene oxide (Ni/rGO) with small size and good dispersibility were successfully prepared by controlling the pyrolysis temperature of the precursor at 450 °C, assisted by a microwave-assisted hydrothermal method, and exhibited enhanced electrocatalytic activity towards oxygen reduction reaction (ORR). Additionally, the electron enrichment on Ni NPs was due to charge transfer from the rGO support to metal nickel, as evidenced by both experimental and theoretical studies. Metal–support interactions between nickel and the rGO support also facilitated charge transfer, contributing to the enhanced ORR performance of the composite material. DFT calculations revealed that the first step (from O₂ to HOO*) was the rate-determining step with an RDS energy barrier lower than that of the Pt(111), indicating favorable ORR kinetics. The HOO* intermediates can be transferred onto rGO by the solid-phase spillover effect, which reduces the chemical adsorption on the nickel surface, thereby allowing continuous regeneration of active nickel sites. The HO₂⁻ intermediates generated on the surface of rGO by 2e⁻ reduction can also efficiently diffuse towards the nearby Ni surface or the interface of Ni/rGO, where they can be further rapidly reduced to OH⁻. This mechanism acts as the pseudo-four-electron path on the RRDE. Furthermore, Ni/rGO-450 demonstrated superior stability, methanol tolerance, and durability compared to a 20 wt% Pt/C catalyst, making it a cost-effective alternative to conventional noble metal ORR catalysts for fuel cells or metal–air batteries. Full article

Polydopamine (PDA) as a melanin-like biomimetic material with excellent biocompatibility, full spectrum light absorption capacity and antioxidation property has been extensively applied in the biomedical field. Based on the high reactivity of dopamine (DA), exploiting new strategies to fabricate novel PDA-based nano-biomaterials with controllable size and improved performance is valuable and desirable. Herein, we reported a facile way to synthesize pyrrole-doped polydopamine-pyrrole nanoparticles (PDA-nPY NPs) with tunable size and enhanced near-infrared (NIR) absorption capacity through self-oxidative polymerization of DA with PY in an alkaline ethanol/H₂O/NH₄OH solution. The PDA-nPY NPs maintain excellent biocompatibility and surface reactivity as PDA. By regulating the volume of added PY, PDA-150PY NPs with a smaller size (<100 nm) and four-fold higher absorption intensity at 808 nm than that of PDA can be successfully fabricated. In vitro and in vivo experiments effectively further demonstrate that PDA-150PY NPs can effectively inhibit tumor growth and completely thermally ablate a tumor. It is believed that these PY doped PDA-nPY NPs can be a potential photothermal (PT) agent in biomedical application. Full article

Increasing the loading density of nanoparticles on carbon support is essential for making Pt-alloy/C catalysts practical in H₂-air fuel cells. The challenge lies in increasing the loading while suppressing the sintering of Pt-alloy nanoparticles. This work presents a 40% Pt-weighted sub-4 nm PtCo/C alloy catalyst via a simple incipient wetness impregnation method. By carefully optimizing the synthetic conditions such as Pt/Co ratios, calcination temperature, and time, the size of supported PtCo alloy nanoparticles is successfully controlled below 4 nm, and a high electrochemical surface area of 93.8 m²/g is achieved, which is 3.4 times that of commercial PtCo/C-TKK catalysts. Demonstrated by electrochemical oxygen reduction reactions, PtCo/C alloy catalysts present an enhanced mass activity of 0.465 A/mg at 0.9 V vs. RHE, which is 2.0 times that of the PtCo/C-TKK catalyst. Therefore, the developed PtCo/C alloy catalyst has the potential to be a highly practical catalyst for H₂–air fuel cells. Full article

The synthesis of highly efficient heterogeneous catalysts with uniformly dispersed noble metal particles and a suitable size is crucial for various industrial applications. However, the high cost and rarity of noble metals limit their economic efficiency, making it essential to improve the catalytic performance with lower noble metal loading. Herein, a two-step method was developed for the synthesis of uniformly dispersed ~3 nm Pt nanoparticles (NPs), strongly anchored on Ni(OH)₂ nanosheets (NSs), which was proven by adequate structural characterizations. XPS analysis demonstrated that Ni(OH)₂ NSs with abundant oxygen vacancies provided sufficient anchor sites for Pt NPs and prevented their agglomeration. The catalytic performance of Pt_n/Ni(OH)₂ (n (represents the addition amount of Pt precursors during the synthesis, μmol) = 5, 10, 15, and 20) NSs with controllable Pt loading were evaluated via the reduction of 4-nitrophenol to 4-aminophenol as a model reaction. The Pt₁₀/Ni(OH)₂ NSs exhibited the best activity and stability, with a reaction rate constant of 0.02358 s⁻¹ and negligible deterioration in ten reaction cycles. This novel synthetic method shows potentials for the synthesis of highly efficient noble-metal-supported catalysts for heterogeneous catalysis. Full article