Platinum Nanoclusters Research Articles

Enzymatic self-wiring in nanopores and its application in direct electron transfer biofuel cells.

A synthetic enzymatic activity in nanopores leading to the direct fabrication of modified electrodes applicable as biosensors and/or biofuel cell elements is reported. We demonstrate the heterogeneous enzymatic implanting of platinum nanoclusters, PtNCs, in glucose oxidase, GOx, immobilized on mesoporous carbon nanoparticles, MPCNP-modified surface. As the pores confine the growth of the clusters, the PtNC@GOx/MPCNP assembly becomes electrically wired to the matrix, demonstrating direct electron transfer, DET, bioelectrocatalytic properties that correlate with the applied duration of synthesis and cluster size. This inside-out nanocluster growth from the cofactor to the matrix is investigated and further compared to a reversed outside-in strategy which follows the electrochemical deposition of the Pt clusters inside the pores and their electrically induced expansion towards the FAD center of the enzyme. While the inside-out and outside-in methodologies provide, for the first time, synthetic bidirectional direct wiring routes of an enzyme to a surface, we highlight an asymmetry in the wiring efficiency associated with the different assemblies. The results indicate the existence of a shorter gap between the FAD cofactor and the PtNCs in the enzymatically implanted assembly, resulting in elevated bioelectrocatalytic currents, lower overpotential, and a higher turnover rate, 2580 e− s−1. The implanted assembly is then coupled to a bilirubin oxidase-adsorbed MPCNP cathode to yield an all-DET biofuel cell. Due to the superior electrical contact of the inside-out-synthesized anode, this cell demonstrates enhanced discharge potential and power outputs as compared to similar systems employing electrochemically synthesized outside-in-grown PtNC-GOx/MPCNPs or even GOx-modified MPCNPs diffusionally mediated by ferrocenemethanol.

Fluorescent Nanoclusters for Imaging of Cells/Stem Cells.

Imaging of cancer cells and cancer stem cells (CSCs) plays an important role in studying cell biology and tracking cancer development and metastasis. There is a wide interest in targeting cancer cells using fluorescent nanoclusters (NCs) capped in protein due to excellent cell viability and photostability, one-step synthesis route, large Stokes shift, good aqueous stability, and easy functionalization capability with long lifetime. Since CD44 is a CSC marker as well as a transmembrane receptor for hyaluronic acid (HA) and many other extracellular matrix (ECM) components, in this protocol, a biocompatible platform was synthesized by conjugation of HA onto luminescent platinum nanoclusters (Pt NCs) in human hemoglobin (Hb) (Hb/Pt NCs). This bioplatform could be used for specific imaging via an efficient targeting of CD44-overexpressing cancer cells and cancer stem cells.

Ultra-small biocompatible jujube polysaccharide stabilized platinum nanoclusters for glucose detection.

The development of noble ultra-small biocompatible Pt nanoclusters (Pt NCs) for glucose detection has been drawing great attention. Herein, ultra-small biocompatible jujube polysaccharide (JP) stabilized platinum nanoclusters (Ptn-JP NCs) are prepared using natural JP as a reducing and solubilizing agent. Ptn-JP NCs were studied for the colorimetric detection of glucose. Ptn-JP NCs (n = 50, 200 and 400) had an average particle diameter of 1-2 nm. Particularly, the measurements of hydrodynamic sizes of Ptn-JP NCs indicated that they maintained good stability in solution for one week. Pt200-JP NCs showed good biocompatibility, and were not toxic against HeLa cells at a high concentration of 400 μg mL-1. Furthermore, Pt200-JP NCs catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with H2O2 to produce blue oxidized TMB (oxTMB). This reaction followed typical Michaelis-Menten kinetics. More importantly, the glucose concentration could be sensitively detected by the color change, and this process was not interfered by other sugars. The linear range for glucose concentration was from 0.01 to 1 mM with a detection limit of 5.47 μM. The glucose concentrations of real samples of serum using Pt200-JP NCs were 9.2, 4.9 and 6.5 mM, respectively. The prepared Ptn-JP NCs have great potential in various biomedical detection methods.

Direct observations of shape fluctuation in long-time atomistic simulations of metallic nanoclusters

Metallic nanoclusters are functional materials whose unique physical and chemical properties are sensitively controlled by their shapes and structures. An in-depth understanding of their morphological stability is therefore of crucial importance. It has been well documented by transmission electron microscopy (TEM) studies that metallic nanoclusters can interconvert between different isomers. However, the relevant mechanisms remain elusive because the timescales of such shape fluctuations are too short to be resolved experimentally and yet too long for conventional atomistic simulations. By employing massively parallel accelerated molecular dynamics (AMD) simulations reaching timescales of milliseconds, we provide a clear description of the dynamical processes leading to shape fluctuation in metallic nanoclusters of platinum, silver, copper, and gold at different sizes and temperatures. In all these materials, direct transformations between face-centered-cubic and fivefold symmetric structures (decahedron or icosahedron) are observed away from the melting point. These transitions occur following either a slip-mediated twinning mechanism or a surface-reconstruction driven process. The identified pathways are shown to be reversible, allowing for genuine shape fluctuation processes that do not involve melting or other external factors.

Shape-Controlled Synthesis of Luminescent Hemoglobin Capped Hollow Porous Platinum Nanoclusters and their Application to Catalytic Oxygen Reduction and Cancer Imaging

Engineering hollow and porous platinum nanostructures using biomolecular templates is currently a significant focus for the enhancement of their facet-dependent optical, electronic, and electrocatalytic properties. However, remains a formidable challenge due to lack of appropriate biomolecules to have a structure-function relationship with nanocrystal facet development. Herein, human hemoglobin found to have facet-binding abilities that can control the morphology and optical properties of the platinum nanoclusters (Pt NCs) by regulation of the growth kinetics in alkaline media. Observations revealed the growth of unusual polyhedra by shape-directed nanocluster attachment along a certain orientation accompanied by Ostwald ripening and, in turn, yield well-dispersed hollow single-crystal nanotetrahedrons, which can easily self-aggregated and crystallized into porous and polycrystalline microspheres. The spontaneous, biobased organization of Pt NCs allow the intrinsic aggregation-induced emission (AIE) features in terms of the platinophilic interactions between Pt(II)-Hb complexes on the Pt(0) cores, thereby controlling the degree of aggregation and the luminescent intensity of Pt(0)@Pt(II)−Hb core−shell NCs. The Hb-Pt NCs exhibited high-performance electrocatalytic oxygen reduction providing a fundamental basis for outstanding catalytic enhancement of Hb-Pt catalysts based on morphology dependent and active site concentration for the four-electron reduction of oxygen. The as-prepared Hb-Pt NCs also exhibited high potential to use in cellular labeling and imaging thanks to the excellent photostability, chemical stability, and low cytotoxicity.

Synthesis of Fe3O4@GSH-Pt NCs Core-Shell Microspheres for Latent Fingerprint Detection

Abstract Positively charged Fe3O4 magnetic nanoparticles were obtained by polyethyleneimine (PEI) as a modification agent. Negatively charged platinum nanoclusters (Pt NCs) were prepared with glutathione (GSH) as reducing agent and protective agent. Finally, spherical fluorescent magnetic nano core-shell microspheres Fe3O4@GSH-Pt NCs were produced through electrostatic adsorption. The magnetic strength was 23.9 emu/g and the fluorescence quantum yield was 8.139%. The experimental results showed that the mean diameter of Fe3O4@GSH-Pt NCs was about 110.3 nm. It emitted red fluorescence at the excitation of 465 nm. Latent fingerprints were directly viewed with excellent ridge details due to the superparamagnetism and excellent fluorescent properties of the prepared Fe3O4@GSH-Pt NCs. Consequently, Fe3O4@GSH-Pt NCs showed great potential in fingerprints detection.

Sulfur oxidation on graphene-supported platinum nanocluster arrays

Nanocluster arrays grown on a graphene Moiré on Rh(1 1 1) are an excellent model system that can bridge the materials gap between single crystals and real catalysts. They feature different adsorption sites like edges, kinks, and facets, but are at the same time well-ordered with a small size distribution. Herein, we used platinum nanocluster arrays to investigate the oxidation of sulfur, which is a common catalyst poison, as a possible route to restore the catalyst. We studied the kinetics in a site-resolved manner with high-resolution XPS, despite the complex shape of the nanoparticles. Since SO3 and SO4 were the only observable SOx surface species, the reaction of S to SO was identified as the rate-determining step. As a secondary process, the displacement of sulfur from edge to facet sites caused by oxygen was observed.

Synthesis and Characterization of Platinum-Praseodymium Oxide Nanocatalysts for Methanol Oxidation

Direct methanol fuel cells (DMFCs) are promising energy conversion devices, which can provide high efficiency and energy density, and as such, have been studied intensively. Due to the poisoning of Pt catalysts during methanol oxidation, various co-catalysts have been studied. Ruthenium has been studied extensively and good results have been obtained. More recently various oxide materials have been proposed and studied. Of these materials, rare earth metal oxides have been shown to be promising co-catalysts, although of the various oxides, CeO2 has perhaps received most attention. In this study, praseodymium oxide containing catalyst materials have been synthesised and characterized. Praseodymium oxide containing nanocatalysts were obtained via deposition of praseodymium hydroxide onto a carbon support material and calcination of the resulting material. Thereafter, platinum nanoclusters were deposited onto the praseodymium oxide containing composite material by impregnation of the Pt precursor into the support material and further reduction with hydrogen. The studied materials were electrochemically characterized using rotating disk electrode, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy methods. Physical properties of the materials were characterized using X-ray diffraction, thermogravimetric analysis, scanning electron microscopy with EDX, inductively coupled plasma mass spectrometry and specific surface area measurements. The studied materials exhibit high currents for methanol oxidation even at low Pt loadings. Compared to a commercial Pt-C(Vulcan) material, the overpotential was drastically reduced, and the peak potential for methanol oxidation is at E = 0.15 V vs mercury-mercurous sulfate electrode. The good results of the study are a continuation of the investigation of nanocatalysts containing rare earth metal oxides for electrooxidation of alcohols. Acknowlegements This work was supported by the EU through the European Regional Development Fund Project TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011) and by the Estonian Research Council (institutional research grant IUT20-13, and PUT1581). P. Valk thanks Estonian Students Fund in USA for financial support.

N-Containing Carbon Nanospheres As PEFC Catalyst Support Prepared from Nature Inspired Precursor

Apart from superior electrocatalytic activity for ORR, nitrogen containing carbon materials are also well-known for their ability to anchoring Pt nanoparticles. It was hypothesized that polydopamine (PDA), an intrinsically N-containing nature inspired polymer, may be able to stabilize platinum nanoclusters due to the binding ability between its amino and catechol groups with Pt precursor. In addition, the inherent fluorescence property of PDA makes it a suitable candidate to study catalyst layer micro-structure and pore size distribution by employing fluorescence microscopy. In this study, PDA was used as a precursor to synthesize ordered carbon nanospheres (100~150 nm) as a catalyst support for polymer electrolyte membrane fuel cells (PEFCs). Morphology of the catalyst was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence microscopy. TEM micrograph (Figure 1) indicated that well-dispersed and uniformly distributed Pt nanoparticles (2-3 nm) was deposited on the PDA based carbon nanospheres (cPDA) as theorized. Electrochemical activity including reaction kinetics of the catalyst was tested in both aqueous and polymer electrolyte (fuel cell condition) media. The performance of the catalyst in a fuel cell was studied at different operating conditions (temperature, relative humidity) and compared with that of the conventional vulcan carbon-based catalyst. Pt durability was assessed in both liquid electrolyte (0.5M H2SO4) and FC condition by conducting US department of energy (DOE) recommended accelerated stress test (AST) protocols. The presentation will share the details of catalyst synthesis and characterization as well as the results of its performance in a fuel cell. Figure 1

Selective bio-labeling and induced apoptosis of hematopoietic cancer cells using dual-functional polyethylenimine-caged platinum nanoclusters

In the past decades, platinum (Pt) is employed to clinical treatment of various cancers. However, for Pt-based drugs, especially Pt in +2 state [Pt (II)], such as cisplatin, number of drawbacks impede their anticancer efficiency including poor pharmacology, fast blood clearance, systemic toxicities causing from poor specificity and excretion of drug through kidneys. Herein, we developed dual-functional ultrafine polyethylenimine caged platinum nanoclusters (PEI-caged Pt NCs), which were utilized in biological imaging of the suspension cells system as fluorescent markers, and selective inhibition of hematopoietic malignancies as anticancer chemotherapeutics simultaneously. These zerovalent Pt NCs are capable to selectively enter into blood cancer cells (K562, BV173 cell lines) when compared to the peripheral blood mononucleated cells (PBMCs) from healthy donors, in addition, it can specifically induce pro-apoptotic protein expression (p53, PUMA, cleaved caspase) in hematopoietic cancer cells and promote cell apoptosis. Avoiding the adding of other fluorescent bio-markers, these Pt NCs showed great potential in diagnosis and treatment of hematopoietic system disease, such as acute myeloid leukemia, lymphoma, myeloma, etc.

Preparation of self-assembled platinum nanoclusters to combat Salmonella typhi infection and inhibit biofilm formation.

In this work, phytoprotein functionalized platinum nanoparticles (PtNCs) were synthesized using the proteins from fresh green spinach leaves. Transmission electron microscopy showed that PtNCs were spherical shape with size ∼5 nm, which self assembled into spherical platinum nanoclustures (PtNCs) with size within the range of 100-250 nm. The presence of elemental platinum was confirmed by EDX analysis. FTIR studies confirm that the PtNCs were stabilized by the protein. As prepared PtNCs inhibits the growth of the food borne pathogen, Salmonella typhi with minimum inhibitory concentration (MIC) of 12.5 μM. Light microscopy evidenced that the PtNCs can damage the established biofilms. Antibacterial mechanistic study revealed that PtNCs damages the S. typhi membranes, which was confirmed by scanning electron microscopy and further by fluorescence microscopy using acridine orange/propidium iodide dual staining assay. Besides membrane damage, PtNCs also triggered the intracellular ROS-mediated oxidative damage over the antioxidant defense and kills S. typhi. The hemolytic test showed low cytotoxicity of PtNCs at 100 μM (four times higher the MIC). Finally, the therapeutic efficacy of PtNCs was validated in S. typhi infected zebrafish animal model and the obtained results are discussed.

Mobility and Poisoning of Mass-Selected Platinum Nanoclusters during the Oxygen Reduction Reaction

A major challenge in electrocatalysis is to understand the effect of electrochemical processes on the physicochemical properties of nanoparticle or nanocluster (NC) ensembles, especially for complex processes, such as the oxygen reduction reaction (ORR) considered herein. We describe an approach whereby electrocatalysis at a small number of well-defined mass-selected Pt NCs (Pt923±37, diameter, d ≈ 3 nm), deposited from a cluster beam source on carbon-coated transmission electron microscopy (TEM) grids, can be measured by a scanning electrochemical cell microscopy (SECCM) setup, in tandem with a range of complementary microscopy and spectroscopy techniques. The SECCM setup delivers high mass transport rates and allows the effects of transient reactive intermediates to be elucidated for different Pt surface coverages (NC spacing). A major observation is that the ORR activity decreases during successive electrochemical (voltammetric) measurements. This is shown to be due to poisoning of the Pt NCs by carbon...

Free-Standing 3D Porous N-Doped Graphene Aerogel Supported Platinum Nanocluster for Efficient Hydrogen Production from Ammonia Electrolysis

Ammonia oxidation reaction (AOR) is an environmentally friendly electrochemical technology for hydrogen production. Nowadays, exploiting low-costing, high-performance and robust catalysts for AOR is essential to improve the overall efficiency of ammonia electrolysis cell (AEC). Here, we report the synthesis and characterization of a novel free-standing three-dimensional (3D) porous N-doped graphene aerogel (NGA) anchored with Pt nanocluster (Pt/NGA) monolithic material as a high-performance and robust electrocatalyst for hydrogen production from AEC. The NGA substrate was facilely fabricated through a self-assemble process into the randomly arranged 3D porous backbone structure with graphene oxide (GO) and poly(oxypropylene)diamine D400 as precursors in a pure water solvent. Then, the Pt nanocluster-like structures were uniformly dispersed and embedded onto NGA through the simple electrodeposition method. The as-prepared Pt/NGA monolithic materials exhibited a higher ammonia electro-oxidation activity wit...

Reactivity of CO on Sulfur-Passivated Graphene-Supported Platinum Nanocluster Arrays

Graphene-supported nanocluster arrays are interesting model systems to bridge the materials gap to real catalysts. This model system was used to investigate the poisoning of platinum particles by sulfur, which is crucial for many industrial processes. The adsorption and desorption of the probe molecule CO on sulfur-poisoned platinum nanoparticles on graphene were studied using high-resolution X-ray photoelectron spectroscopy. We observed a strong blocking of edge adsorption sites and a weaker blocking of on-top sites on facets; bridge sites are only blocked at higher sulfur coverages. During heating, CO diffuses to edge sites, thereby displacing the sulfur to the facets. Our results show interesting similarities to stepped platinum single crystals.

Quantum-Chemical Analysis of the Mechanism of Degradation of Binary Platinum Nanoclusters with Sulfur-Containing Compounds

We propose a quantum-chemical model of poisoning of binary Pt42Me13 platinum nanoclusters (where Me is a transition metal, namely, Fe, Co, or Ni) with core-shell structure by hydrogen sulfide and sulfur dioxide in media of low-temperature fuel cells. This model is based on the evaluation of the adsorption characteristics of interaction of H2S and SO2 molecules with the surfaces of nanoclusters. It is shown that their susceptibility to the formation of strong chemisorption bonds with H2S and SO2 molecules depends on the type of nanocluster core and the sites of adsorption on their surfaces. By using the quantum-chemical method of density functional, we establish the regularities of influence of the cores of binary nanoclusters of transition metals Fe, Co, or Ni on the geometric and energy characteristics of the adsorption of molecules. We also propose the mechanism of interaction of H2S and SO2 molecules with binary platinum nanoclusters based on the changes in the electronic properties of the surface platinum atoms or in the distribution of active adsorption centers on the surface of nanoclusters depending on the type of the core. The accumulated results confirm the prospects of the density functional method in the theoretical evaluation of the influence of chemical composition and the structure of binary nanoparticles on their properties in the reactions of low-temperature fuel cells.

Size-Effect on Electrochemical Hydrogen Evolution Reaction by Single-Size Platinum Nanocluster Catalysts Immobilized on Strontium Titanate

Size-specific chemical properties of metal nanoclusters (NCs) have motivated their applications in catalysis, whose properties were found to be dramatically different from bulk materials. We have reported herein the size-dependent activity of platinum (Pt) NCs for the electrochemical hydrogen-evolution-reaction (HER) in neutral water. The single-size NC catalysts were prepared by the soft-landing of mass-selected Pt NCs on a strontium titanate (SrTiO3) (100) surface using an intensive, size-selective NC source based on high-power impulse magnetron sputtering. Successful fabrications of single-size Pt NC catalysts were confirmed with scanning tunneling microscopy. It was found from electrochemical measurements that catalytic HER activity per unit Pt shows a maximum at Pt30 in the range of n = 1–45. Taking into account the electron affinities of Pt NCs measured by gas-phase anion photoelectron spectroscopy, the reaction mechanism of HER is deduced: the size-specific HER activity originates from the matching of energy levels of Pt NCs with the band structure of SrTiO3 surfaces.

Enhanced electrocatalytic performance for the hydrogen evolution reaction through surface enrichment of platinum nanoclusters alloying with ruthenium in situ embedded in carbon

PtRu alloy nanoparticles, surface-enriched with Pt nanoclusters and partially-embedded in carbon, act as the cost-effective and promising alternative to commercial Pt/C for electrocatalytic hydrogen evolution.

Cooperative Multifunctional Catalysts for Nitrone Synthesis: Platinum Nanoclusters in Amine-Functionalized Metal-Organic Frameworks.

Nitrones are key intermediates in organic synthesis and the pharmaceutical industry. The heterogeneous synthesis of nitrones with multifunctional catalysts is extremely attractive but rarely explored. Herein, we report ultrasmall platinum nanoclusters (PtNCs) encapsulated in amine-functionalized Zr metal-organic framework (MOF), UiO-66-NH2 (Pt@UiO-66-NH2 ) as a multifunctional catalyst in the one-pot tandem synthesis of nitrones. By virtue of the cooperative interplay among the selective hydrogenation activity provided by the ultrasmall PtNCs and Lewis acidity/basicity/nanoconfinement endowed by UiO-66-NH2 , Pt@UiO-66-NH2 exhibits remarkable activity and selectivity, in comparison to Pt/carbon, Pt@UiO-66, and Pd@UiO-66-NH2 . Pt@UiO-66-NH2 also outperforms Pt nanoparticles supported on the external surface of the same MOF (Pt/UiO-66-NH2 ). To our knowledge, this work demonstrates the first examples of one-pot synthesis of nitrones using recyclable multifunctional heterogeneous catalysts.

Cooperative Multifunctional Catalysts for Nitrone Synthesis: Platinum Nanoclusters in Amine‐Functionalized Metal–Organic Frameworks

AbstractNitrones are key intermediates in organic synthesis and the pharmaceutical industry. The heterogeneous synthesis of nitrones with multifunctional catalysts is extremely attractive but rarely explored. Herein, we report ultrasmall platinum nanoclusters (PtNCs) encapsulated in amine‐functionalized Zr metal–organic framework (MOF), UiO‐66‐NH2 (Pt@UiO‐66‐NH2) as a multifunctional catalyst in the one‐pot tandem synthesis of nitrones. By virtue of the cooperative interplay among the selective hydrogenation activity provided by the ultrasmall PtNCs and Lewis acidity/basicity/nanoconfinement endowed by UiO‐66‐NH2, Pt@UiO‐66‐NH2 exhibits remarkable activity and selectivity, in comparison to Pt/carbon, Pt@UiO‐66, and Pd@UiO‐66‐NH2. Pt@UiO‐66‐NH2 also outperforms Pt nanoparticles supported on the external surface of the same MOF (Pt/UiO‐66‐NH2). To our knowledge, this work demonstrates the first examples of one‐pot synthesis of nitrones using recyclable multifunctional heterogeneous catalysts.

Efficient in situ growth of platinum nanoclusters on the surface of Fe3O4 for the detection of latent fingermarks

Hydrophobic Fe3O4 nanoparticles were modified with polyethyleneimine (PEI) to obtain hydrophilic Fe3O4 nanoparticles. By reducing the content of H2PtCl6 solution by using l-ascorbic acid (AA) as a reductive agent, fluorescent platinum nanoclusters (Pt NCs) were incubated into the PEI-modified Fe3O4 nanoparticles. The prepared Fe3O4@Pt NCs microspheres possessed a uniform size, improved monodispersity, high magnetization (40.8 emu/g) and high fluorescence quantum yield (9.0%). Moreover, compared to the reported methods, this method demonstrated that the incubation of Pt NCs on the surface of PEI-Fe3O4 was more convenient and needed less reaction time (about 10 min). The experimental results showed that latent fingermarks developing with Fe3O4@Pt NCs powder exhibit excellent ridge details. The Fe3O4@Pt NCs with superparamagnetism and excellent fluorescence showed great potential in forensic science.