Precious Metal Nanoparticles Research Articles

Copper foam in situ loaded with precious metal nanoparticles as transmission SEIRAS substrate for rapid detection of dithiocarbamate pesticides.

A transmission surface-enhanced infrared absorption spectroscopy (SEIRAS) substrate based on copper foam (CF) was developed for the rapid detection of dithiocarbamate (DTC) pesticides. The transmission SEIRAS substrate was prepared by immersing CF in a mixed solution of a precious metal solution and a polyvinyl pyrrolidone (PVP) solution. Then CF could be in situ loaded with precious metal nanoparticles (MNPs) by PVP-modified displacement reaction in seconds. PVP could be helpful for the uniform distribution of MNPs. Experimental parameters were evaluated with 11-mercaptoundecanoic acid (MUA) as a probe molecule, including the concentration of the precious metal solution, the amount of PVP, and the reaction time. Taking CF loaded with gold nanoparticles (Au NPs-CF) as an example, the signal intensity of DTC pesticide (Ziram) could be enhanced by two orders of magnitude, and the R2 of the calibration curve was 0.999. In addition, the Pt NPs-CF substrate was applied to the rapid detection of other DTC pesticides (Ferbam). In summary, we have developed a new method to prepare the transmission SEIRAS substrate and apply it to the rapid detection of DTC pesticides in liquid.

UV-induced syntheses of surfactant-free precious metal nanoparticles in alkaline methanol and ethanol.

Surfactant-free UV-induced syntheses of Pt and Ir nanoparticles in alkaline methanol and ethanol are presented. Small size nanoparticles ca. 2 nm in diameter are obtained without surfactants in a wide range of base concentration.

TiO2 inverse opal structures with facile decoration of precious metal nanoparticles for enhanced photocatalytic activity

TiO2 inverse opal (IO) structures were fabricated by an infiltration method that were functionalized with gold, silver, and gold-silver core-shell metal nanoparticles. The photocatalytic activity of the TiO2 IO structures with metal nanoparticles was characterized by gas-phase conversion of acetylene into carbon dioxide. All metal nanoparticle functionalized structures showed an increase in photocatalytic activity via surface plasmon resonance coupling of the incident light. The highest photocatalytic activity was observed with gold-silver core-shell nanoparticle functionalized TiO2 IO structure (increase of 62% compared to reference TiO2 IO) followed by gold (53%) and silver (39%) nanoparticles.

Electrocatalysis of Oxygen Reduction Reaction on Shape-Controlled Pt and Pd Nanoparticles-Importance of Surface Cleanliness and Reconstruction.

Shape-controlled precious metal nanoparticles have attracted significant research interest in the recent past due to their fundamental and scientific importance. Because of their crystallographic-orientation-dependent properties, these metal nanoparticles have tremendous implications in electrocatalysis. This review aims to discuss the strategies for synthesis of shape-controlled platinum (Pt) and palladium (Pd) nanoparticles and procedures for the surfactant removal, without compromising their surface structural integrity. In particular, the electrocatalysis of oxygen reduction reaction (ORR) on shape-controlled nanoparticles (Pt and Pd) is discussed and the results are analyzed in the context of that reported with single crystal electrodes. Accepted theories on the stability of precious metal nanoparticle surfaces under electrochemical conditions are revisited. Dissolution, reconstruction, and comprehensive views on the factors that contribute to the loss of electrochemically active surface area (ESA) of nanoparticles leading to an inevitable decrease in ORR activity are presented. The contribution of adsorbed electrolyte anions, in-situ generated adsorbates and contaminants toward the ESA reduction are also discussed. Methods for the revival of activity of surfaces contaminated with adsorbed impurities without perturbing the surface structure and its implications to electrocatalysis are reviewed.

Corrosion-Resistant Precious Metal Coated Oxide Nanoparticles As Supports for Iridium-Based Oxygen Evolution Reaction Catalysts in Proton Exchange Membrane Electrolyzers

Presently, the most efficient catalysts chosen for proton exchange membrane water electrolyzers (PEMWE) are platinum group metal (PGM) based, and the required high mass loading of these metals makes the technology expensive at large scale.1 Thus, it is desirable to find alternative catalysts or structures that can lower PGM loading while maintaining efficient PEMWE operation. The anodic oxygen evolution reaction (OER) of a PEMWE suffers from a high catalyst loading as a result of lack of stable catalyst supports that can withstand the highly corrosive electrochemical conditions. These supports would help disperse the PGMs within the catalyst layer. The current practice is to use unsupported iridium based nanoparticles as catalysts since most supports degrade under such harsh conditions. However, only surface atoms participate in electrocatalysis, leaving the bulk of the iridium as an expensive PGM support that functions solely as a conductive matrix. Replacing the core with less expensive and resource constrained materials that can be conductive yet stable under the highly oxidizing OER conditions is very desirable. Unfortunately, doping or defecting oxides to make them conductive hinders their stability, so other tactics must be utilized.2 In this talk we will present our work on materials prepared by coating insulating titanium dioxide nanoparticles (< 100 nm) with small amounts of conductive platinum or gold nanoparticles to prepare supports for iridium catalysts. Under OER conditions, all three materials are stable. In order to synthesize these structures, we identified synthesis routes to prepare well dispersed layers of these precious metal nanoparticles onto the titanium dioxide nanoparticles; making them the optimal substitute metals for an iridium core. These nanostructures were then coated with iridium to prepare supported OER catalysts with the desired activity and stability. Three synthetic procedures were implemented and compared in order to determine the most efficient way to prepare the nanoparticle composites, i.e. wetness impregnation, citric acid reduction, and light catalyzed deposition. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) were utilized to characterize the nanoparticles. XRD suggested that the final catalyst material did indeed contain a combination of crystalline titanium dioxide, iridium, and metal gold or platinum nanoparticles. SEM and EDS indicated that the iridium, as well as the gold or platinum nanoparticles, were well distributed upon the larger titanium dioxide nanoparticles. It was determined that the best distribution was found when using platinum nanoparticles and the photo reduction synthesis technique. The complete synthesis methods, characterization of the materials, as well as electrocatalytic performance towards OER using rotating disk electrode in acidic electrolyte, will be presented in this poster.

A Predictable Catalyst Model for Highly Active and Selective Catalysis of Hydrogenation of Nitroarenes: Comprehension of Various Precious Metal Nanoparticles

AbstractVarious precious metal catalysts have been commonly used in catalytic reactions, but the differences and likeness between their catalytic performances are rarely systematically studied. Therefore, we have prepared the Pd, Pt, Rh, Ru, Au, and Ag/Fe3O4 catalysts, and the similarities and differences of various catalysts are analyzed by XRD, FT‐IR, TEM, HR‐TEM, XPS, BET, and VSM characterizations. Besides that platinum is the best catalyst component, the Pd and Rh/Fe3O4 catalysts also exhibit excellent catalytic activity and chemoselectivity, but the Ru, Au, Ag‐containing catalysts show poor catalytic performance for hydrogenation of 4‐nitrophenol. According to the kinetic study, we have demonstrated that the reaction orders for Pd, Pt, and Rh are 0.8, 0.8, and 1.5, respectively. This result reveals that the activity of Pd, Pt, and Rh‐containing catalysts can be precisely predicted. Moreover, our catalytic system is fascinating with many advantages such as environmental friendliness, mild reaction conditions, and the magnetic separability.

Strong metal-support interaction promoted via constructing biocarbon membrane for enhanced CO preferential oxidation activity of Rh/CaCO3@biocarbon

Precious metal nanoparticles, widely used as heterogeneous catalysts, are easy to aggregate and deactivate, restricting their applications in many important catalytic fields like preferential CO oxidation (CO-PROX) in H2-rich stream. In this work, well dispersed Rh nanoclusters anchored on CaCO3@biocarbon derived from waste eggshell (ESMC) were synthesized through a step carbonization and incipient wetness impregnation process. The obtained catalysts exhibited 3D macroporous architecture, which is favorable for exposure of more nucleation sites of precious metal Rh, thus minimizing the aggregation of Rh particles. Furthermore, a thick carbon shell attached to eggshells, with interesting electronic structure and surface chemistry, efficiently transfers electrons between Rh and biocarbon@CaCO3 support, and enhances the interaction between Rh NPs and support. Both effects synergistically allow Rh/ESMC to equip more active adsorption sites-asymmetric Rh(CO)2 gem-dicarbonyl, thus greatly promoting the catalytic performance of Rh/ESMC in CO-PROX (operation temperature window: 140–240 °C). The present finding offers an environmentally friendly approach to fabricate well dispersed Rh nanoclusters catalysts, and it can be extended to rationally design other supported metal nanoparticle catalysts.

Monovalent Alkali Cations: Simple and Eco-Friendly Stabilizers for Surfactant-Free Precious Metal Nanoparticle Colloids

The Co4Cat approach is a surfactant-free industry-relevant method to synthesize precious metal nanoparticles with enhanced catalytic properties. Colloidal nanoparticles are obtained by reduction of...

Synthesis and Characterization of Composite Membranes Based on Carbon Functionalized with Gold Nanoparticles

The purpose of this experimental laboratory work is to obtain composite membranes having carbon and gold nanoparticles in the matrix. Consideration was made of using graphene oxide, a material which, under certain conditions, can generate membranes by a self-assembly process under vacuum in an aqueous or organic medium. The cellulose acetate (CA) - graphene oxide (GO) composite membranes have been functionalized with gold nanoparticles (AuNP) by two technological processes: thermal evaporation and ultrasonic mixing of stable graphene oxide and gold suspensions. The stable suspensions containing gold nanoparticles were obtained by chemical reduction of aqueous solutions of Tetrachloroauric acid trihydrate (HAuCl4) precursors with sodium citrate under high temperature conditions. Dispersibility of carbon nanostructures and precious metal nanoparticles has been studied with a DLS granulometer - Malvern Instruments Zetasizer ZS90. It was determined the mean particle size and Zeta potential function of the suspensions pH. The graphite based membranes were further subjected to various characterizations techniques. It was found that both the surfaces and the cross-sections were functionalized with gold particles. The presence of Au particles was revealed both on the membrane surface and also inside its structure. Hydrophilic tests demonstrate that the membrane filters have potential to be used in various applications.

Magnetically separable rhodium nanoparticles as catalysts for releasing hydrogen from the hydrolysis of ammonia borane

Magnetically separable catalysts attract considerable attention in catalysis due to their facile separation from the reaction medium. This propensity is crucial for efficient multiple use of precious noble metal nanoparticles in catalysis. In fact, the isolation of catalysts from the reaction medium by filtration and washing results usually in the loss of huge amount of activity in the subsequent run of catalysis. Although many transition metal nanoparticle catalysts have been reported for the H2 generation from the hydrolysis of ammonia borane, there is no study reporting the magnetically separable rhodium based catalysts for the hydrolytic dehydrogenation of ammonia borane. Here, we report the preparation of rhodium(0) nanoparticles supported on the surface of Fe3O4 and CoFe2O4 magnetic nanopowders as the first example of magnetically separable rhodium nanocatalysts. The resulting magnetically separable Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles are highly active, long-lived and reusable catalysts in H2 generation from the hydrolysis of ammonia borane providing a turnover frequency value of 273 and 720 min−1, respectively, at 25.0 ± 0.1 °C. These magnetically separable catalysts show high reusability and long-term stability in the hydrolysis reaction. They retain their complete initial activity even after the 5th use releasing exactly 3.0 equivalent H2 gas per mole of ammonia borane. The long-term stability tests show that Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles provide a total turnover number of 125,000 and 245,000, respectively, in releasing H2 from the hydrolysis of ammonia borane at room temperature. The long term stability and reusability of magnetically separable Rh0/Fe3O4 and Rh0/CoFe2O4 nanoparticles make them attractive catalysts for hydrogen generation in fuel cell applications.

Oxidative decomposition of volatile organic compound on hydroxyapatite with oriented crystal structures

Hydroxyapatite (HAp) exhibits superior biocompatibility, ion-exchange ability and high adsorption property has attracted much attention as one of the most well-known ceramic functional materials. We have previously reported the efficient oxidative decomposition of volatile organic compounds (VOC) on commercial HAp powders, which makes HAp a promising alternative material of precious metal nanoparticle catalyst for environmental purification. In this work, HAp with oriented crystal growth of a-plane and c-plane were synthesized via air-liquid interface precipitation in solution, and the influence of crystal orientation on VOC decomposition performance was systemically investigated. As a result, HAp with preferential growth of c-plane performs higher catalytic VOC decomposition activity, which can be attributed to the large number of active radicals generated on surface despites the relative smaller sufficient surface area. The results in this study highlight the important relation between crystal structure of HAp and the decomposition activity of VOC, which also provide useful information for the structure design of ceramic functional materials.

Precious metal nanoparticles supported on KOH pretreated activated carbon under microwave radiation as a catalyst for selective hydrogenation of cinnamaldehyde

A series of precious metals (Pd, Pt, Ru, Rh, and Au) supported on commercial activated carbon (AC) catalysts were prepared and their catalytic performance in the selective hydrogenation of cinnamaldehyde (CAL) were evaluated. Among these catalysts, Pt supported on AC pretreated by 10 % KOH under microwave radiation has the highest catalytic activity and selectivity in the selective hydrogenation of CAL, which provided a selectivity to cinnamyl alcohol of 73.4 % with a conversion of CAL of 62.8 %. The structure and morphology of the AC and the precious metal supported catalysts were characterized by BET, FT‐IR, XPS, XRD, and TEM. The catalytic performances of various precious metals as active components were compared. The effects of reaction temperature, hydrogen pressure, and reaction time on the catalytic hydrogenation of CAL were investigated. The by‐products were analyzed by GC‐MS and their formation mechanism was proposed. This work provides an efficient method of using commercial AC as the support for preparing promising catalysts in the selective hydrogenation of CAL.

Controlled Synthesis of Surfactant-Free Water-Dispersible Colloidal Platinum Nanoparticles by the Co4Cat Process.

The recently reported Co4Cat process is a synthesis method bearing ecological and economic benefits to prepare precious-metal nanoparticles (NPs) with optimized catalytic properties. In the Co4Cat process, a metal precursor (e.g., H2 PtCl6 ) is dissolved in an alkaline solution of a low-boiling-point solvent (methanol) and reduced to NPs at low temperature (<80 °C) without the use of surfactants. Here, the Co4Cat process to prepare Pt NPs is described in detail. The advantages of this new synthesis method for research and development but also industrial production are highlighted in a comparison with the popular "polyol" synthesis. The reduction of H2 PtCl6 from PtIV to PtII and further to Pt0 is followed by UV/Vis and XANES/EXAFS measurements. It is demonstrated how the synthesis can be accelerated, how size control is achieved, and how the colloidal dispersions can be stabilized without the use of surfactants. Despite being surfactant-free, the Pt NPs exhibit surprisingly long-term (up to 16 months) stability in water over a wide pH range (4-12) and in aqueous buffer solutions. The Co4Cat process is thus relevant to produce NPs for heterogeneous catalysis, electro-catalysis, or bio/medical applications.

Atomically dispersed iron hydroxide anchored on Pt for preferential oxidation of CO in H2.

Proton-exchange-membrane fuel cells (PEMFCs) are attractive next-generation power sources for use in vehicles and other applications1, with development efforts focusing on improving the catalyst system of the fuel cell. One problem is catalyst poisoning by impurity gases such as carbon monoxide (CO), which typically comprises about one per cent of hydrogen fuel2-4. A possible solution is on-board hydrogen purification, which involves preferential oxidation of CO in hydrogen (PROX)3-7. However, this approach is challenging8-15 because the catalyst needs to be active and selective towards CO oxidation over a broad range of low temperatures so that CO is efficiently removed (to below 50 parts per million) during continuous PEMFC operation (at about 353 kelvin) and, in the case of automotive fuel cells, during frequent cold-start periods. Here we show that atomically dispersed iron hydroxide, selectively deposited on silica-supported platinum (Pt) nanoparticles, enables complete and 100 per cent selective CO removal through the PROX reaction over the broad temperature range of 198 to 380 kelvin. We find that the mass-specific activity of this system is about 30 times higher than that of more conventional catalysts consisting of Pt on iron oxide supports. In situ X-ray absorption fine-structure measurements reveal that most of the iron hydroxide exists as Fe1(OH)x clusters anchored on the Pt nanoparticles, with density functional theory calculations indicating that Fe1(OH)x-Pt single interfacial sites can readily react with CO and facilitate oxygen activation. These findings suggest that in addition to strategies that target oxide-supported precious-metal nanoparticles or isolated metal atoms, the deposition of isolated transition-metal complexes offers new ways of designing highly active metal catalysts.

Energy Production and Storage Promoted by Organometallic Complexes

Organometallic complexes have intrinsically excellent characteristics as a new class of electrocatalyst for clean energy production in fuel cells and electrolyzers. The state‐of‐the‐art materials for these devices are based on precious metal nanoparticles dispersed on conductive carbon‐based supports. Although such materials have reached very high performance levels in terms of activity and stability, they suffer from some intrinsic limitations that contribute to hinder the commercial development of fuel cells and electrolyzers on a large scale. Organometallic‐based electrocatalysts may help to overcome such limitations. For example, they exhibit high selectivity in alcohol and sugar electrooxidation. Additionally, precious metal loadings can be reduced significantly using single site organometallic catalysts where each metal atom is potentially active. In this review, we will discuss various literature examples of organometallic electrocatalysts employed as anodes for fuel cells and electrolyzers and as cathodes for the hydrogen evolution reaction (HER). We will focus our attention on the few examples of electrocatalysts that have been successfully used in complete cells.

“Green” synthesis of nanoparticles of precious metals: antimicrobial and catalytic properties

The paper presents the use of agricultural products, namely grape skins, in the “green” synthesis of monometallic (Au, Ag) and bimetallic (Au-Ag) nanoparticles (NPs) from aqueous solutions of metal ions of the corresponding precursors. At present, there exist urgent problems of utilization of waste from the agro-industrial complex, rational use of nature and transition to the use of environment-friendly and energy-efficient technologies. Therefore, there is a tendency to use “green” technologies in obtaining nanomaterials that are considered environment-friendly and resource-saving. The study has proved the efficiency of using food waste (grape skins) as a reducing and stabilizing agent in forming nanoparticles of precious metals of mono- and bimetallic structures. Biological raw materials were extracted in an aqueous medium under a short-term effect of low-temperature plasma discharges. On the basis of the complex analysis of the extract composition, it was proved that the hydroxyl, carbonyl and carboxyl functional groups of the organic compounds of the grape skin extract are responsible for the recovery of the metal ions and stabilization of the resulting NPs. The research has proved that mono- and bimetallic NPs are formed with the following peaks: for Ag 0 (λ max =440 nm), Au 0 (λ max =540 nm), and Ag-Au (λ max =510 nm). The size and stability of the nanoparticles obtained by the “green” synthesis were assessed in comparison with the same parameters for the plasmochemical method of nanoparticles’ formation. The study has revealed antibacterial, catalytic and anti-corrosion properties of the synthesized nanoparticles. The resulting monometallic (Au, Ag) and bimetallic (Au–Ag) nanoparticles show excellent catalytic activity while recovering p-nitrophenol (4-NPh) to p-aminophenol (4-APh) in the presence of NaBH 4 . The synthesized NPs demonstrate their antibacterial activity against gram-positive and gram-negative bacteria. The findings allow to expand the practical application of metal nanoparticles in various industries and enhance the processing and reuse of non-liquid waste

Making the Most of Precious Metal Nanoparticles in the Purification of Industrial Wastewater by Catalytic Wet Air Oxidation

The aim of catalytic wet air oxidation is to use air to remove organic contaminants from wastewater through their complete oxidation, without having to vaporise the water. To date, the widespread exploitation of this process has been held back by the low activity of available catalysts, which means that it has to be operated at above-atmospheric pressure in order to keep the water in the liquid phase at the elevated temperatures required to achieve complete oxidation. Here we present an overview of an ongoing study examining the key requirements of both the active phase and the support material in precious metal catalysts for wet air oxidation, using phenol as the model contaminant. The major outcome to date is that the results reveal a synergy between platinum and hydrophobic support materials, which is not apparent when the active phase is ruthenium.

Colloids for Catalysts: A Concept for the Preparation of Superior Catalysts of Industrial Relevance.

Compared to conventional preparation methods for supported heterogeneous catalysts, the use of colloidal nanoparticles (NPs) allows for a precise control over size, size distribution, and distribution/location of the NPs on the support. However, common colloidal syntheses have restrictions that limit their applicability for industrial catalyst preparation. We present a simple, surfactant‐free, and scalable preparation method for colloidal NPs to overcome these restrictions. We demonstrate how precious‐metal NPs are prepared in alkaline methanol, how the particle size can be tuned, and how supported catalysts are obtained. The potential of these colloids in the preparation of improved catalysts is demonstrated by two examples from heterogeneous catalysis and electrocatalysis.

Surfactant-Free Preparation of Ir Based Oer Catalysts in Low Boiling Point Solvents and Their Catalytic Evaluation

We introduce a simple and scalable preparation method for colloidal precious metal nanoparticles (NPs) that overcomes the typical restrictions in catalyst synthesis, i.e. the independent control of individual parameters such as size, size-distribution, and particle density (metal loading). Our Co4Cat (Colloids for Catalysts) synthesis concept uses alkaline low-boiling point solvents without the use of additional surfactants. It can be applied to different mono- and multimetallic precious metal NPs as well as different support types. In the presented work, the Co4Cat concept is used to prepare Ir based NPs that are tested as oxygen evolution reaction (OER) catalysts for water electrolysis under acidic conditions. In electrochemical half-cell tests, it is shown that due to the very high surface area, exceptional mass activities can be achieved. The Co4Cat concept is an advancement of our “toolbox” synthesis approach that was previously applied to Pt based PEM fuel cell catalysts. In the presentation, the general idea as well as the individual synthesis steps are discussed in detail and the electrochemical testing is benchmarked against literature values as well as commercially available OER catalysts.

Conversion of confined metal@ZIF-8 structures to intermetallic nanoparticles supported on nitrogen-doped carbon for electrocatalysis

We report a facile strategy to synthesize intermetallic nanoparticle (iNP) electrocatalysts via one-pot pyrolysis of a zeolitic imidazolate framework, ZIF-8, encapsulating precious metal nanoparticles (NPs). ZIF-8 serves not only as precursor for N-doped carbon (NC), but also as Zn source for the formation of intermetallic or alloy NPs with the encapsulated metals. The resulting sub-4 nm PtZn iNPs embedded in NC exhibit high sintering resistance up to 1,000 °C. Importantly, the present methodology allows fine-tuning of both composition (e.g., PdZn and RhZn iNPs, as well as AuZn and RuZn alloy NPs) and size (2.4, 3.7, and 5.4 nm PtZn) of the as-formed bimetallic NPs. To the best of our knowledge, this is the first report of a metal-organic framework (MOF) with multiple functionalities, such as secondary metal source, carbon precursor, and size-regulating reagent, which promote the formation of iNPs. This work opens a new avenue for the synthesis of highly uniform and stable iNPs.