ABSTRACT
In this paper, we reported the synthesis and characterization of CoNiCuCrS nanoparticle alloys using scanning transmission electron microscopy (STEM) techniques. The nanoparticles form hexagonal platelets with an average size of 34.5 nm. Atomic resolution STEM imaging reveals an ordered FCC crystal structure with a lattice parameter of 0.93 nm, consistent with a (CuCo)6Ni3Cr1S13.333 intermetallic phase. The paper provided direct experimental evidence of the strain distribution at the atomic scale using advanced STEM techniques. The findings are consistent with previous studies, confirming the presence of small but significant strains in high entropy alloys (HEAs). By studying nanoparticles, we achieved atomic-resolution imaging and characterization, which is challenging with bulk HEA samples. The work revealed that defects like stacking faults and partial dislocations, stabilized by the presence of sulphur in our sample, play an important role in the mechanical properties of HEAs. This research demonstrated that nanoparticles can be used as a model for studying bulk properties of HEAs, providing insights into local strain effects and crystal growth dynamics.
ABSTRACT
Herein, we report the synthesis of novel platinum-based nanoparticles with step-pyramidal growth induced by poly(diallyldimethylammonium chloride) (PDDA). The complex stepped pyramidal shape became the central point for outstanding catalytic reduction of 4-nitrophenol, overcoming the activity of bare Pt nanoparticles. These results are valuable for the catalytic degradation of reactive molecules.
ABSTRACT
The field of nanoalloys has been advancing at a rapid pace in the last two decades. Many new characterization methods and theoretical advances have produced a substantial knowledge of the nanoalloys' properties and structure. Most of the work has been limited to binary alloys. A path forward for the field will be the study of nanoalloys with three or more metals. Adding new components will produce new properties and possibly more fabrication controls. In this paper, we will discuss the challenges that will arise in multi-metallic nanoalloys. We will show that entropy and twin boundaries play a dominant role in multi-metallic alloys.
ABSTRACT
The COVID-19 pandemic demonstrated the critical need for accurate and rapid testing for virus detection. This need has generated a high number of new testing methods aimed at replacing RT-PCR, which is the golden standard for testing. Most of the testing techniques are based on biochemistry methods and require chemicals that are often expensive and the supply might become scarce in a large crisis. In the present paper we suggest the use of methods based on physics that leverage novel nanomaterials. We demonstrate that using Surface Enhanced Raman Spectroscopy (SERS) of virion particles a very distinct spectroscopic signature of the SARS-CoV-2 virus can be obtained. We demonstrate that the spectra are mainly composed by signals from the spike (S) and nucleocapsid (N) proteins. It is believed that a clinical test using SERS can be developed. The test will be fast, inexpensive, and reliable. It is also clear that SERS can be used for analysis of structural changes on the S and N proteins. This will be an example of application of nanotechnology and properties of nanoparticles for health and social related matters.
ABSTRACT
Copper-platinum alloys are important binary alloys in catalysis. In this communication, we demonstrate that it is possible to preserve the thermal properties of platinum with a copper-platinum alloy by converting the substitutional alloy into an interstitial one. This conversion occurs when the size of the copper-platinum system is reduced down to the nanoscale. The size-dependent phase diagram of Cu-Pt for a spherical nanoparticle is calculated at various sizes (50, 10 and 5 nm) demonstrating that Cu-Pt alloyed nanoparticles can be formed all over the composition range. Experimentally, the electron microscopy characterization of copper-platinum alloyed nanoparticles synthesized by wet chemistry supports the predicted structural transition.
ABSTRACT
The increasing impact of metallic nanoparticles on life sciences has stimulated the development of new techniques and multiple improvements to the existing methods of manufacturing nanoparticles with tailored properties. Nanoparticles can be synthesized through a variety of physical and chemical methods. The choice of preparation procedure will depend on the physical and chemical characteristics required in the final product, such as size, dispersion, chemical miscibility, and optical properties, among others. Here we review basic practical procedures used for the preparation of protected and unprotected metallic nanoparticles and describe a number of experimental procedures based on colloidal chemistry methods. These include gold nanoparticle synthesis by reduction with trisodium citrate, ascorbic acid, or sugars in aqueous phase and nanoparticle passivation with alkanethiols, CTAB, or BSA. We also describe microwave-assisted synthesis, nanoparticle synthesis in ethylene glycol, and template-assisted synthesis with dendrimers, and, briefly, how to control nanoparticle shape (star-shaped and branched nanoparticles).
Subject(s)
Gold/chemistry , Metal Nanoparticles/chemistry , Ascorbic Acid/chemistry , Citrates/chemistry , Microwaves , Particle SizeABSTRACT
Growth of anisotropic nanostructures enables the manipulation of optical properties across the electromagnetic spectrum by fine morphological tuning of the nanoparticles. Among them, stellated metallic nanostructures present enhanced properties owing to their complex shape, and hence, the control over the final morphology becomes of great importance. Herein, a seed-mediated method for the high-yield production of goldrich-copper concave branched nanostructures and their structural and optical characterization is reported. The synthesis protocol enabled excellent control and tunability of the final morphology, from concave pentagonal nanoparticles to five-fold branched nanoparticles, named "nanostars". The anisotropic shape was achieved via kinetic control over the synthesis conditions by selective passivation of facets using a capping agent and assisted by the presence of copper chloride ions, both having a crucial impact over the final structure. Optical extinction measurements of nanostars in solution indicated a broad spectral response, hiding the properties of the individual nanostars. Hence, single-particle scattering measurements of individual concave pentagonal nanoparticles and concave nanostars were performed to determine the origin of the multiple plasmon bands by correlation with their morphological features, following their growth evolution. Finite-difference time-domain calculations delivered insights into the geometry-dependent plasmonic properties of concave nanostars and their packed aggregates. Our results uncover the intrinsic scattering properties of individual nanostars and the origin of the broad spectral response, which is mostly due to z-direction packed aggregates.
ABSTRACT
Anisotropic gold nanoparticles offer potential applications due to their functionalities and shape-dependent properties. Reshaping noble metal nanoparticles is an interesting field with optical, surface-enhanced Raman spectroscopy, catalytic applications and potential application as a photothermic therapy. This work comprises a structural study on gold nano bipyramids (Au NBPs) and nanodumbbells, and the evolution of Au NBPs capped with cetyltrimethylammonium bromide and dodecanethiol through an in situ and ex situ heating process in high vacuum. Also, we study the reshaping of Au NBPs by the addition of Pt to study the surface modification and the strain generated on a single particle by geometric phase analysis.
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We report the efficient wet-chemical production of self-assembled gold-copper bimetallic nanoparticles (diameter of â¼2 nm) into two-dimensional flexible ribbonlike nanostructures. The direct observation of a layered arrangement of particles into nanoribbons was provided through high-resolution transmission electron microscopy and electron tomography. These nanoribbons showed photoluminesce and efficient photocatalytic activity for the conversion of 4-nitrophenol. The thermal stability of the nanoribbons was also measured by in situ heat treatment in the electron microscope, confirming that the self-assembled gold-copper nanoribbons efficiently supported up to 350 °C. The final morphology of the nanoparticles and their ability to self-assemble into flexible nanoribbons were dependent on concentration and the ratio of precursors. Therefore, these experimental factors were discussed. Remarkably, the presence of copper was found to be critical to triggering the self-assembly of nanoparticles into ordered layered structures. These results for the synthesis and stability of self-assemblies of metallic nanoparticles present a potential extension of the method to producing materials with catalytic applications.
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We report the synthesis of MWNT/ZnO hybrid nanostructures. A simple, affordable, chemical procedure to functionalize MWNTs with ZnO nanoparticles was performed. A significant portion of the surface of MWNTs was covered with ZnO nanoparticles; these particles formed highly porous spherical nodules of 50-150 nm in diameter, sizes that are an order of magnitude larger than similar ZnO nanonodules reported in the literature. Hence, the self-assembled nanocomposite the ZnO exhibited a large surface-to-volume ratio, which is a very advantageous property for potential catalytic applications. The resultant MWNT/ZnO nanocomposites were characterized by x-ray diffraction, scanning and high-resolution transmission electron microscopy, and UV-vis and Raman spectroscopy. The temperature coefficient of resistance (TCR) of the nanocomposites was measured and reported. The average TCR value goes from -5.6%/K up to -18%/K, over temperature change intervals from 10 K to 1 K. Based on these TCR results, the nanocomposite MWNT/ZnO prepared in this work is a promising material, with potential application as a bolometric sensor.
ABSTRACT
In this work, we report the synthesis and detailed structural characterization of novel helical gold-copper nanowires. The nanowires possess the Boerdijk-Coxeter-Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density of twin boundaries and stacking faults. To the best of our knowledge, such gold-copper nanowires have never been reported previously.
Subject(s)
Copper/chemistry , Gold/chemistry , Nanowires/ultrastructure , Amines/chemistry , Glucose/chemistry , Models, Molecular , Nanotechnology/methods , Nanowires/chemistryABSTRACT
The alloy Au-Ag system is an important noble bimetallic phase, both historically (as "Electrum") and now especially in nanotechnology, as it is applied in catalysis and nanomedicine. To comprehend the structural characteristics and the thermodynamic stability of this alloy, a knowledge of its phase diagram is required that considers explicitly its size and shape (morphology) dependence. However, as the experimental determination remains quite challenging at the nanoscale, theoretical guidance can provide significant advantages. Using a regular solution model within a nanothermodynamic approach to evaluate the size effect on all the parameters (melting temperature, melting enthalpy, and interaction parameters in both phases), the nanophase diagram is predicted. Besides an overall shift downward, there is a "tilting" effect on the solidus-liquidus curves for some particular shapes exposing the (100) and (110) facets (cube, rhombic dodecahedron, and cuboctahedron). The segregation calculation reveals the preferential presence of silver at the surface for all the polyhedral shapes considered, in excellent agreement with the latest transmission electron microscopy observations and energy dispersive spectroscopy analysis. By reviewing the nature of the surface segregated element of different bimetallic nanoalloys, two surface segregation rules, based on the melting temperatures and surface energies, are deduced. Finally, the optical properties of Au-Ag nanoparticles, calculated within the discrete dipole approximation, show the control that can be achieved in the tuning of the local surface plasmon resonance, depending of the alloy content, the chemical ordering, the morphology, the size of the nanoparticle, and the nature of the surrounding environment.
Subject(s)
Alloys/chemistry , Gold/chemistry , Metal Nanoparticles/chemistry , Silver/chemistry , Metal Nanoparticles/ultrastructure , Microscopy, Electron, Transmission , Nanotechnology , Particle Size , Phase Transition , Surface Plasmon Resonance , Temperature , ThermodynamicsABSTRACT
Nanoalloys have emerged as multi-functional nanoparticles with applications in biomedicine and catalysis. This work reports the efficient production and the advanced transmission electron microscopy characterization of gold-copper pentagonal nanostars. The morphology of the branches is controlled by the adequate choice of the capping agent. When oleylamine is used rounded nanostars are produced, while pointed nanostars are obtained by using hexadecylamine. Both types of nanostars were proved to be thermally stable and could therefore be used as therapeutic agents in photo-thermal therapies as confirmed by the near-infrared absorption spectra.
Subject(s)
Copper/chemistry , Gold/chemistry , Metal Nanoparticles/chemistry , Metal Nanoparticles/ultrastructure , Hyperthermia, Induced/methods , Microscopy, Electron, Transmission , Phototherapy/methodsABSTRACT
The antimicrobial properties of silver nanoparticles (AgNPs) have made these particles one of the most used nanomaterials in consumer products. Therefore, an understanding of the interactions (unwanted toxicity) between nanoparticles and human cells is of significant interest. The aim of this study was to assess the in vitro cytotoxicity effects of silver nanoclusters (AgNC, < 2 nm diameter) on peripheral blood mononuclear cells (PBMC). Using flow cytometry and comet assay methods, we demonstrate that exposure of PBMC to AgNC induced intracellular reactive oxygen species (ROS) generation, DNA damage and apoptosis at 3, 6 and 12 h, with a dose-dependent response (0.1, 1, 3, 5 and 30 µg ml(-1)). Advanced electron microscopy imaging of complete and ultrathin-sections of PBMC confirmed the cytotoxic effects and cell damage caused by AgNC. The present study showed that AgNC produced without coating agents induced significant cytotoxic effects on PBMC owing to their high aspect ratio and active surface area, even at much lower concentrations (<1 µg ml(-1)) than those applied in previous studies, resembling what would occur under real exposure conditions to nanosilver-functionalized consumer products.
Subject(s)
Leukocytes, Mononuclear/drug effects , Metal Nanoparticles/toxicity , Silver/toxicity , Adult , Apoptosis/drug effects , Cells, Cultured , Colony-Forming Units Assay , Comet Assay , DNA Damage , Female , Flow Cytometry , Humans , In Vitro Techniques , Inflammation/chemically induced , Inflammation/pathology , Male , Microscopy, Electron , Particle Size , Reactive Oxygen Species/metabolism , Surface Properties , Young AdultABSTRACT
Silver nanoparticles offer a possible means of fighting antibacterial resistance. Most of their antibacterial properties are attributed to their silver ions. In the present work, we study the actions of positively charged silver nanoparticles against both methicillin-sensitive Staphylococcus aureus and methicillin-resistant Staphylococcus aureus. We use aberration-corrected transmission electron microscopy to examine the bactericidal effects of silver nanoparticles and the ultrastructural changes in bacteria that are induced by silver nanoparticles. The study revealed that our 1 nm average size silver nanoparticles induced thinning and permeabilization of the cell wall, destabilization of the peptidoglycan layer, and subsequent leakage of intracellular content, causing bacterial cell lysis. We hypothesize that positively charged silver nanoparticles bind to the negatively charged polyanionic backbones of teichoic acids and the related cell wall glycopolymers of bacteria as a first target, consequently stressing the structure and permeability of the cell wall. This hypothesis provides a major mechanism to explain the antibacterial effects of silver nanoparticles on Staphylococcus aureus. Future research should focus on defining the related molecular mechanisms and their importance to the antimicrobial activity of silver nanoparticles.
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Highly monodispersed Cu-Pt bimetallic nanoclusters were synthesized by a facile synthesis approach. Analysis of transmission electron microscopy (TEM) and spherical aberration (C s)-corrected scanning transmission electron microscopy (STEM) images shows that the average diameter of the Cu-Pt nanoclusters is 3.0 ± 1.0 nm. The high angle annular dark field (HAADF-STEM) images, intensity profiles, and energy dispersive X-ray spectroscopy (EDX) line scans, allowed us to study the distribution of Cu and Pt with atomistic resolution, finding that Pt is embedded randomly in the Cu lattice. A novel simulation method is applied to study the growth mechanism, which shows the formation of alloy structures in good agreement with the experimental evidence. The findings give insight into the formation mechanism of the nanosized Cu-Pt bimetallic catalysts.
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Trimetallic nanoparticles possess different properties than their mono- and bi-metallic counterparts, opening a wide range of possibilities for diverse potential applications with the notion to study possible morphology, atomic ordering, reduce precious metal consumption and many others. In this paper, we present a comprehensive experimental study on AuCu-Pt trimetallic nanoparticles with an average diameter of 15 ± 1.0 nm, synthesized in a one-pot synthesis method and characterized by the Cs-corrected scanning transmission electron microscopy technique that allowed us to probe the structure at the atomic level resolution. A new way to control the nanoparticle morphology by the presence of third metal (Pt) is also discussed by the overgrowth of Pt on the as prepared AuCu core by Frank-van der Merwe (FM) layer-by-layer and Stranski-Krastanov (SK) island-on-wetting-layer growth modes. With the application of this research, we are now a step closer to produce optimum catalysts in which the active phase forms only surface monolayers. In addition, the nanoalloy exhibits high index facet surfaces with {211} and {321} families that are highly open-structure surfaces and are interesting for the catalytic applications.
Subject(s)
Copper/chemistry , Gold/chemistry , Metal Nanoparticles/chemistry , Platinum/chemistry , Microscopy, Electron, Scanning Transmission , Surface PropertiesABSTRACT
We report the synthesis, structural characterization, and atomistic simulations of AgPd-Pt trimetallic (TM) nanoparticles. Two types of structure were synthesized using a relatively facile chemical method: multiply twinned core-shell, and hollow particles. The nanoparticles were small in size, with an average diameter of 11 nm and a narrow distribution, and their characterization by aberration corrected scanning transmission electron microscopy allowed us to probe the structure of the particles at an atomistic level. In some nanoparticles, the formation of a hollow structure was also observed, that facilitates the alloying of Ag and Pt in the shell region and the segregation of Ag atoms on the surface, affecting the catalytic activity and stability. We also investigated the growth mechanism of the nanoparticles using grand canonical Monte Carlo simulations, and we have found that Pt regions grow at overpotentials on the AgPd nanoalloys, forming 3D islands at the early stages of the deposition process. We found very good agreement between the simulated structures and those observed experimentally.
ABSTRACT
Behavior of matter at the nanoscale differs from that of the bulk due to confinement and surface effects. Here, we report a direct observation of liquid-like behavior of a single grain boundary formed by cold-welding Au nanoparticles, 40 nm in size, by mechanical manipulation in situ TEM. The grain boundary rotates almost freely due to the free surfaces and can rotate about 90 degrees. The grain boundary sustains more stress than the bulk, confirming a strong bonding between the nanoparticles. Moreover, this technique allows the measurement of the surface diffusion coefficient from experimental observations, which we compute for the Au nanoparticles. This methodology can be used for any metal, oxide, semiconductor or combination of them.