Oxidation is a corrosion reaction where the corroded metal forms an oxide. Prevention of oxidation at the nanoscale is critically important to retain the physicochemical properties of metal nanoparticles. In this work, we studied the stability of polyethylene glycol (PEG) coated copper nanoparticles (PEGylated CuNPs) against oxidation. The freshly-prepared PEGylated CuNPs mainly consist of metallic Cu which are quite stable in air although their surfaces are typically covered with a few monolayers of cuprous oxide. However, they are quickly oxidized in water due to the presence of protons that facilitate oxidation of the cuprous oxide to cupric oxide. PEG with carboxylic acid terminus could slightly delay the oxidation process compared to that with thiol terminus. It was found that a solvent with reducing power such as ethanol could greatly enhance the stability of PEGylated CuNPs by preventing further oxidation of the cuprous oxide to cupric oxide and thus retain the optical properties of CuNPs. The reducing environment also assists the galvanic replacement of these PEGylated CuNPs to form hollow nanoshells; however, they consist of ultra-small particle assemblies due to the co-reduction of gold precursor during the replacement reaction. As a result, these nanoshells do not exhibit strong optical properties in the near-infrared region. This study highlights the importance of solvent effects on PEGylated nonprecious metal nanoparticles against oxidation corrosion and its applications in preserving physicochemical properties of metallic nanostructures.
more »
« less
Copper Template Design for the Synthesis of Bimetallic Copper–Rhodium Nanoshells through Galvanic Replacement
Galvanic replacement reactions are widely used in the synthesis of bimetallic nanoshells. Essential to these syntheses is the design of template materials with electrochemical potentials that are low enough to facilitate the replacement of a wide variety of metals. While Cu is an attractive template from this standpoint, it has only rarely been used due to its propensity for oxidation and the associated difficulties in achieving chemically stable colloids. Here, a synthetic scheme is demonstrated for the design of supported Cu templates and their subsequent replacement with Rh where the detrimental influences of oxidation are not only mitigated but used to place shape and compositional controls on the reaction product. It is shown that the CuRh nanoshells can be produced that are shaped as substrate‐truncated nanocubes or cuboctahedrons depending upon the degree of exposure that the Cu templates have to dissolved oxygen. Moreover, it is demonstrated that the intentional surface oxidation of the Cu template followed by Cu2O removal results in galvanic replacement reactions yielding porous nanoshells with far greater Rh replacement. The study forwards the design of Cu templates for galvanic replacement reactions and presents opportunities for their use in other template‐mediated syntheses.
more » « less- NSF-PAR ID:
- 10051089
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Particle & Particle Systems Characterization
- Volume:
- 35
- Issue:
- 5
- ISSN:
- 0934-0866
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Galvanic replacement (GR) of monometallic nanoparticles (NPs) provides a versatile route to interesting bimetallic nanostructures, with examples such as nanoboxes, nanocages, nanoshells, nanorings, and heterodimers reported. The replacement of bimetallic templates by a more noble metal can generate trimetallic nanostructures with different architectures, where the specific structure has been shown to depend on the relative reduction potentials of the participating metals and lattice mismatch between the depositing and template metal phases. Now, the role of reaction stoichiometry is shown to direct the overall architecture of multimetallic nanostructures produced by GR with bimetallic templates. Specifically, the number of initial metal islands deposited on a NP template depends on the reaction stoichiometry. This outcome was established by studying the GR process between intermetallic PdCu (i-PdCu) NPs and either AuCl 2 − (Au 1+ ) or AuCl 4 − (Au 3+ ), producing i-PdCu–Au heterostructures. Significantly, multiple Au domains form in the case of GR with AuCl 2 − while only single Au domains form in the case of AuCl 4 − . These different NP architectures and their connection to reaction stoichiometry are consistent with Stranski–Krastanov (SK) growth, providing general guidelines on how the conditions of GR processes can be used to achieve multimetallic nanostructures with different defined architectures.more » « less
-
null (Ed.)Galvanic replacement reactions are a reliable method for transforming monometallic nanotemplates into bimetallic products with complex nanoscale architectures. When replacing bimetallic nanotemplates, even more complex multimetallic products can be made, with final nanocrystal shapes and architectures depending on multiple processes, including Ostwald ripening and the Kirkendall effect. Galvanic replacement, therefore, is a promising tool in increasing the architectural complexity of multimetallic templates, especially if we can identify and control the relevant processes in a given system and apply them more broadly. Here, we study the transformation of intermetallic PdCu nanoparticles in the presence of HAuCl 4 and H 2 PtCl 6 , both of which are capable of oxidizing both Pd and Cu. Replacement products consistently lost Cu more quickly than Pd, preserved the crystal structure of the original intermetallic template, and grew a new phase on the sacrificial template. In this way, atomic and nanometer-scale architectures are integrated within individual nanocrystals. Product morphologies included faceting of the original spherical particles as well as formation of core@shell and Janus-style particles. These variations are rationalized in terms of differing diffusion behaviors. Overall, galvanic replacement of multimetallic templates is shown to be a route toward increasingly exotic particle architectures with control exerted on both Angstrom and nanometer-scale features, while inviting further consideration of template and oxidant choices.more » « less
-
more » « less
Rationale Purification of recombinant proteins is a necessary step for functional or structural studies and other applications. Immobilized metal affinity chromatography is a common recombinant protein purification method. Mass spectrometry (MS) allows for confirmation of identity of expressed proteins and unambiguous detection of enzymatic substrates and reaction products. We demonstrate the detection of enzymes purified on immobilized metal affinity surfaces by direct or ambient ionization MS, and follow their enzymatic reactions by direct electrospray ionization (ESI) or desorption electrospray ionization (DESI).
Methods A protein standard, His‐Ubq, and two recombinant proteins, His‐SHAN and His‐CS, expressed in
Escherichia coli Results Small proteins (His‐Ubq) and medium proteins (His‐SAHN) could readily be detected from 96‐well plates by direct infusion ESI, or from microscope slides by DESI‐MS after purification on surface from clarified
E. coli cell lysate. Protein oxidation was observed for immobilized proteins on both Cu‐NTA and Ni‐NTA; however, this did not hamper the enzymatic reactions of these proteins. Both the nucleosidase reaction products for His‐SAHN and the methylation product of His‐CS (theobromine to caffeine) were detected.Conclusions The immobilization, purification, release and detection of His‐tagged recombinant proteins using immobilized metal affinity surfaces for direct infusion ESI‐MS or ambient DESI‐MS analyses were successfully demonstrated. Recombinant proteins were purified to allow identification directly out of clarified cell lysate. Biological activities of the recombinant proteins were preserved allowing the investigation of enzymatic activity via MS.
-
Water electrolysis using renewable energy inputs is being actively pursued as a green route for hydrogen production. However, it is limited by the high energy consumption due to the sluggish anodic oxygen evolution reaction (OER) and safety issues associated with H2 and O2 mixing. Here, we replaced OER with an electrocatalytic oxidative dehydrogenation (EOD) of aldehydes for bipolar H2 production and achieved industrial-level current densities at cell voltages much lower than during water electrolysis. Experimental and computational studies suggest a reasonable barrier for C-H dissociation on Cu surfaces, mainly through a diol intermediate, with a potential-dependent competition with the solution-phase Cannizzaro reaction. The kinetics of EOD reaction was further enhanced by a porous CuAg catalyst prepared from a galvanic replacement method. Through Ag incorporation and its modification of the Cu surface, the geometric current density and electrocatalyst durability were significantly improved. Finally, we engineered a bipolar H2 production system in membrane-electrode assembly-based flow cells to facilitate mass transport, achieving a maximum current density of 248 and 390 mA cm−2 at cell voltages of 0.4 V and 0.6 V, respectively. The faradaic efficiency of H2 from both cathode and anode reactions both attained ~100%. Taking advantage of the bipolar H2 production without the issues associated with H2/O2 mixing, an inexpensive, easy-to-manufacture dialysis porous membrane was demonstrated to substitute the costly anion exchange membrane, achieving an energy-efficient and cost-effective process in a simple reactor for H2 production. The estimated H2 price of $2.51/kg from an initial technoeconomic assessment is competitive with US DoE’s “Green H2” targets.more » « less
