Synthesis Of Metal Nanostructures Research Articles

Laser Synthesis of Catalytically Active Materials for Organic Synthesis and Sensor Technology

Introduction: The catalytic activity of metallic nanomaterials depends on their surface morphology. A widely known method is the laser synthesis of metal nanostructures by depositing on dielectric surfaces from aqueous solutions containing metal complexes. The article analyzes the factors that favor the production of conductive, catalytic, and sensory-active deposits by laser method. It is shown that the two main factors is the presence of a large number of charged defects on heterophase surfaces and the structure of metal-containing complexes in solution. This is typical for mono- and bimetallic alloys, the components of which interact with the laser beams according to the autocatalytic type. Using the example of laser deposition from solutions of Co, Ni, Fe, Zn, and Ag salts with homo- and heterophase dielectrics, the sensory and catalytic properties of the deposits are compared by impedance spectroscopy and voltammetry. It has been shown that heterophase precipitation significantly enhances the catalysis response. Background: It is known that the highest catalytic activity exhibits nanostructured and highly porous materials with a large specific surface area and materials containing surface heterogeneity in the form of charged acid-base centers. Such materials are necessary for the creation of new catalysts for organic synthesis and for the creation of new sensor materials for enzyme-free microbiosensors. Active development of new methods for the synthesis of such materials is underway. But not all of them give the expected result. Methods: Laser synthesis methods have the best prospects, including the method of laser-induced metal deposition. This is the laser synthesis of metal nanostructures by depositing dielectric surfaces from aqueous solutions containing metal complexes. Results: Аrticle analyzes the factors that favor the production of conductive, catalytic, and sensory-active deposits by laser method. It is shown that the two main factors are the presence of a large number of charged defects on heterophase surfaces and the structure of a metal-contained complex in solution. This is typical for mono- and bimetallic alloys, the components of which interact with the laser beam according to the autocatalytic type. Using the example of laser deposition from solutions of Co, Ni, Fe, Zn, and Ag salts with homo- and heterophase dielectrics, the sensory and catalytic properties of the deposits are compared by impedance spectroscopy and voltammetry. Conclusion: It has been shown that heterophase precipitation significantly enhances the catalysis response. It is shown that the laser deposition reaction has an autocatalytic mechanism in a dynamic mode. The results of autocatalysis can be used in a stationary mode to create a microbiosensor for glucose, as well as to create a technology for laser refining rare metals and hydrogen energy in a dynamic mode.

Synthesis of Metallic Nanostructures Using Ionizing Radiation and Their Applications.

This paper reviews the radiation-induced synthesis of metallic nanostructures and their applications. Radiolysis is a powerful method for synthesizing metallic nanoparticles in solution and heterogeneous media, and it is a clean alternative to other existing physical, chemical, and physicochemical methods. By varying parameters such as the absorbed dose, dose rate, concentrations of metallic precursors, and nature of stabilizing agents, it is possible to control the size, shape, and morphology (alloy, core-shell, etc.) of the nanostructures and, consequently, their properties. Therefore, the as-synthesized nanoparticles have many potential applications in biology, medicine, (photo)catalysis, or energy conversion.

Nanoarchitectonics of Metallene Materials for Electrocatalysis.

Controlling the synthesis of metal nanostructures is one approach for catalyst engineering and performance optimization in electrocatalysis. As an emerging class of unconventional electrocatalysts, two-dimensional (2D) metallene electrocatalysts with ultrathin sheet-like morphology have gained ever-growing attention and exhibited superior performance in electrocatalysis owing to their distinctive properties originating from structural anisotropy, rich surface chemistry, and efficient mass diffusion capability. Many significant advances in synthetic methods and electrocatalytic applications for 2D metallenes have been obtained in recent years. Therefore, an in-depth review summarizing the progress in developing 2D metallenes for electrochemical applications is highly needed. Unlike most reported reviews on the 2D metallenes, this review starts by introducing the preparation of 2D metallenes based on the classification of the metals (e.g., noble metals, and non-noble metals) instead of synthetic methods. Some typical strategies for preparing each kind of metal are enumerated in detail. Then, the utilization of 2D metallenes in electrocatalytic applications, especially in the electrocatalytic conversion reactions, including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, fuel oxidation reaction, CO2 reduction reaction, and N2 reduction reaction, are comprehensively discussed. Finally, current challenges and opportunities for future research on metallenes in electrochemical energy conversion are proposed.

Galvanic Replacement Synthesis of Metal Nanostructures: Bridging the Gap between Chemical and Electrochemical Approaches

ConspectusGalvanic replacement synthesis involves oxidation and dissolution of atoms from a substrate while the salt precursor to another material with a higher reduction potential is reduced and deposited on the substrate. The driving force or spontaneity of such a synthesis comes from the difference in reduction potential between the redox pairs involved. Both bulk and micro/nanostructured materials have been explored as substrates for galvanic replacement synthesis. The use of micro/nanostructured materials can significantly increase the surface area, offering immediate advantages over the conventional electrosynthesis. The micro/nanostructured materials can also be intimately mixed with the salt precursor in a solution phase, resembling the setting of a typical chemical synthesis. The reduced material tends to be directly deposited on the surface of the substrate, just like the situation in an electrosynthesis. Different from an electrosynthesis where the two electrodes are spatially separated by an electrolyte solution, the cathodes and anodes are situated on the same surface, albeit at different sites, even for a micro/nanostructured substrate. Since the oxidation and dissolution reactions occur at sites different from those for reduction and deposition reactions, one can control the growth pattern of the newly deposited atoms on the same surface of a substrate to access nanostructured materials with diverse and controllable compositions, shapes, and morphologies in a single step. Galvanic replacement synthesis has been successfully applied to different types of substrates, including those made of crystalline and amorphous materials, as well as metallic and nonmetallic materials. Depending on the substrate involved, the deposited material can take different nucleation and growth patterns, resulting in diverse but well-controlled nanomaterials sought for a variety of studies and applications.In this Account, we recapitulate our efforts over the past two decades in fabricating metal nanostructures for a broad range of applications by leveraging the unique capability of galvanic replacement synthesis. We begin with a brief introduction to the fundamentals of galvanic replacement between metal nanocrystals and salt precursors, followed by a discussion of the roles played by surface capping agents in achieving site-selected carving and deposition for the fabrication of various bimetallic nanostructures. Two examples based on the Ag-Au and Pd-Pt systems are selected to illustrate the concept and mechanism. We then highlight our recent work on the galvanic replacement synthesis involving nonmetallic substrates, with a focus on the protocol, mechanistic understanding, and experimental control for the fabrication of Au- and Pt-based nanostructures with tunable morphologies. Finally, we showcase the unique properties and applications of nanostructured materials derived from galvanic replacement reactions for biomedicine and catalysis. We also offer some perspectives on the challenges and opportunities in this emerging field of research.

Morphological Control: Properties and Applications of Metal Nanostructures

Metal nanomaterials with special physicochemical and plasmatic properties have a wide range of applications in various fields including catalysts, plasmon devices, spectroscopy, fuel cell, and various sensors including chemical, colorimetric, and fluorescence sensors. These applications are made possible by controlling the morphology and properties of nanostructures and increasing their selectivity. Various methods have been developed for the synthesis of metal nanostructures, including the use of prefabricated patterns or hard templates such as anodic aluminum oxide and soft molds such as cetyltrimethylammonium bromide (CTAB).

Oriented Attachment: A Unique Mechanism for the Colloidal Synthesis of Metal Nanostructures

AbstractRational synthesis of nanostructures with desired properties critically depends on our understanding of the growth mechanism. In addition to the traditional mechanism involving atomic addition, oriented attachment (OA) has received increasing attention in recent years. Employing nanocrystallites as building blocks, OA offers an important route to anisotropic growth, inclusion of defects, and formation of nanostructures with branched morphology. With a focus on metals, here we offer a brief account of recent progress in understanding OA and how it can be adapted for the colloidal synthesis of nanostructures with diverse compositions and morphologies. We start with a discussion on the current understanding of OA based on computational simulations and experimental studies, followed by typical examples of metal nanostructures produced through OA. Finally, we showcase the catalytic and plasmonic applications enabled by those nanostructures, together with perspectives on the challenges and opportunities.

DNA Nanotechnology-Enabled Fabrication of Metal Nanomorphology.

In recent decades, DNA nanotechnology has grown into a highly innovative and widely established field. DNA nanostructures have extraordinary structural programmability and can accurately organize nanoscale materials, especially in guiding the synthesis of metal nanomaterials, which have unique advantages in controlling the growth morphology of metal nanomaterials. This review started with the evolution in DNA nanotechnology and the types of DNA nanostructures. Next, a DNA-based nanofabrication technology, DNA metallization, was introduced. In this section, we systematically summarized the DNA-oriented synthesis of metal nanostructures with different morphologies and structures. Furthermore, the applications of metal nanostructures constructed from DNA templates in various fields including electronics, catalysis, sensing, and bioimaging were figured out. Finally, the development prospects and challenges of metal nanostructures formed under the morphology control by DNA nanotechnology were discussed.

Gold nanoparticles green synthesis with clove oil: spectroscopic and theoretical study

Certain limitations of obtaining metal nanoparticles with the use of synthetic chemicals have sparked a great interest in scientists to develop green synthesis procedures which use non-toxic and eco-friendly reagents and wastes. Essential oils have the potential to simultaneously act as reducing agents and stabilizers for the synthesis of metal nanoparticles. In the present work, we have synthesized gold nanoparticles (AuNPs) using clove oil (Syzygium aromaticum L. essential oil) as the main reducing agent and stabilizer. The AuNPs solutions were characterized by UV–VIS spectroscopy, and the isolated solid AuNPs were analyzed by Fourier transformed infrared spectroscopy. Various reactivity descriptors determined in terms of Conceptual Density Functional Theory, for the 16 predominant components of clove oil, have been calculated by using the quantum chemical B3LYP/6-311G** level of theory. With the aim to validate the chosen theoretical method, the calculated infrared spectra have been compared with the available experimental spectra. Moreover, the active centers for nucleophilic and electrophilic attacks have been identified through the analysis of atomic partial charges and Fukui function indices. The obtained theoretical results should be considered as a starting point for the prediction of the appropriateness of essential oils for the direct green synthesis of metal nanostructures.

Quantitative Analysis of DNA-Mediated Formation of Metal Nanocrystals.

The predictive synthesis of metal nanocrystals with desired structures relies on the precise control of the crystal formation process. Using a capping ligand is an effective method to affect the reduction of metal ions and the formation of nanocrystals. However, predictively synthesizing nanostructures has been difficult to achieve using conventional capping ligands. DNA, as a class of the promising biomolecular capping ligands, has been used to generate sequence-specific morphologies in various metal nanocrystals. However, mechanistic insight into the DNA-mediated nanocrystal formation remains elusive due to the lack of quantitative experimental evidence. Herein, we quantitatively analyzed the precise control of DNA over Ag+ reduction and the structures of resulting Au-Ag core-shell nanocrystals. We derived the equilibrium binding constants between DNA and Ag+, the kinetic rate constants of sequence-specific Ag+ reduction pathways, and the percentage of active surface sites remaining on the nanocrystals after DNA passivation. These three synergistic factors influence the nucleation and growth process both thermodynamically and kinetically, which contributed to the morphological evolution of Au-Ag nanocrystals synthesized with different DNA sequences. This study demonstrates the potential of using functional DNA sequences as a versatile and tunable capping ligand system for the predictable synthesis of metal nanostructures.

Synthesis of Metal Nanostructures Using Supercritical Carbon Dioxide: A Green and Upscalable Process.

Metallic nanostructures have numerous applications as industrial catalysts and sensing platforms. Supercritical carbon dioxide (scCO2 ) is a green medium for the scalable preparation of nanomaterials. Supercritical fluid reactive deposition (SFRD) and other allied techniques can be employed for the mass production of metal nanostructures for various applications. The present article reviews the recent reports on the scCO2 -assisted preparation of zero-valent metal nanomaterials and their applications. A brief description of the science of pure supercritical fluids, especially CO2 , and the basics of binary mixtures composed of scCO2 and a low volatile substance, e.g., an organometallic precursor are presented. The benefits of using scCO2 for preparing metal nanomaterials, especially as a green solvent, are also being highlighted. The experimental conditions that are useful for the tuning of particle properties are reviewed thoroughly. The range of modifications to the classical SFRD methods and the variety of metallic nanomaterials that can be synthesized are reviewed and presented. Finally, the broad ranges of applications that are reported for the metallic nanomaterials that are synthesized using scCO2 are reviewed. A brief summary along with perspectives about future research directions is also presented.

Quantifying Electrocatalytic Reduction of CO2 on Twin Boundaries

Summary A protocol relying on the use of silver nanostructures with well-defined dimensions and morphologies (e.g., nanocubes and nanowires) has been developed to differentiate and quantitatively determine the atom-specific activities of different surface atoms toward catalyzing electrochemical CO2 reduction reaction (CO2RR). The atom-specific activity of the twin-boundary edges (TBEs) is comparable to (or slightly higher than) that of the single-crystal edges (SCEs) formed from the crossing of two {100} surfaces, and it is on the order of ∼16 attoampere/atom (aA/atom) toward electrochemical CO2RR. This value is more than two orders higher than the atom-specific activity of the {100} surface atoms, i.e., ∼0.1 aA/atom. The high catalytic activity of the TBEs, which represent a class of commonly existing surface defects in stable metal nanostructures with face-centered cubic lattices, is consistent with the DFT calculations, in which the bridge-type binding configuration of COOH∗ at the TBEs stabilizes this intermediate to promote overall CO2RR.

Synthesis, Characterization and toxicity Analysis of Novel Silver Nanoparticles from Brassica oleracea var italica (Broccoli)

Epidemiologic studies demonstrate that vegetable consumption decreases the risk of various types of cancers. Crucifers were found to have anti-cancer and antioxidant activities due to their enriched content of glycosylates. Nanotechnology is the design, characterization, production & application of structures, devices, and systems by controlling shape and size at the nanoscale. This work describes a novel combinatorial synthesis approach, which is rapid and simple for the synthesis of metallic nanostructures of novel metals such as silver (Ag) by using a “comparison study of Conventional method (CM) and Microwave (MW) synthesis” method of silver nanoparticles. By the current study, we describe a cost-effective and environment-friendly technique for green synthesis of silver nanoparticles through the extract of Broccoli. AgNPs characterized using UV–Vis absorption spectroscopy was used to monitor the quantitative formation of silver nanoparticles. The characteristics features of the obtained silver nanoparticles were studied using a Scanning electron microscope (SEM), Transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR). Here, we have reported a simple biological and low-cost approach for the preparation of stable silver nanoparticles by bioreduction of silver nitrate solution using Brassica oleracea (Broccoli) aqueous extract. The in-vitro analysis was performed in HEp 2 cell lines against which anti-cancer activity was recorded. Additionally, the antioxidant activity was also found by estimating the antioxidant enzymes. The in vivo toxicity was performed using chick embryos. The important outcome of the study will be the development of value-added products from cruciferous plants like B. oleracea for nanotechnology-based industries.

Simple and Fast High-Yield Synthesis of Silver Nanowires.

Silver nanowires (AgNWs) combine high electrical conductivity with low light extinction in the visible and are used in a wide range of applications, from transparent electrodes, to temperature and pressure sensors. The most common strategy for the production of AgNWs is the polyol synthesis, which always leads to the formation of silver nanoparticles as byproducts. These nanoparticles degrade the performance of AgNWs' based devices and have to be eliminated by several purification steps. Here, we report a simple and fast synthesis of AgNWs with minimal formation of byproducts, as confirmed by the spectral purity of the final solution. Our synthetic strategy relies on the use of freshly prepared AgCl and on the minimization of gas evolution inside the reaction vessel. The observed synthetic improvements can be of general validity for the polyol synthesis of metallic nanostructures of different shapes and compositions.

A novel method to regulate the morphology of silver nanostructure by galvanic replacement reaction with boric acid

A great deal of progress has been made with regard to the morphology and growth mechanism of metal nanostructures, here we report a novel method to control the morphology of silver nanostructures by galvanic replacement reaction with the assistance of boric acid. Silver nanotubes and nanocombs were obtained by varying the concentration and pH value of boric acid. The growth status of silver nanostructure were captured during the process, meanwhile, a novel growth mechanism of silver nanocombs and nanoflowers was proposed. We hypothesized that the boric acid acts as a modified electrode and template molecule in the system. The possible molecular configuration of boric acid, the modification and adsorption of boric acid on the electrode during the galvanic replacement were also investigated. Finally, this paper has demonstrated the versatility of a simple, green and conceptually novel naturally occurring template approach for the controllable synthesis of metal nanostructures.

Controlling the Morphologies of Silver Aggregates by Laser-Induced Synthesis for Optimal SERS Detection.

Controlling the synthesis of metallic nanostructures for high quality surface-enhanced Raman scattering (SERS) materials has long been a central task of nanoscience and nanotechnology. In this work, silver aggregates with different surface morphologies were controllably synthesized on a glass–solution interface via a facile laser-induced reduction method. By correlating the surface morphologies with their SERS abilities, optimal parameters (laser power and irradiation time) for SERS aggregates synthesis were obtained. Importantly, the characteristics for largest near-field enhancement were identified, which are closely packed nanorice and flake structures with abundant surface roughness. These can generate numerous hot spots with huge enhancement in nanogaps and rough surface. These results provide an understanding of the correlation between morphologies and SERS performance, and could be helpful for developing optimal and applicable SERS materials.

Nanostructures of noble metals as functional materials in biosensors

Recent advancement in nanoscience and nanotechnologies inspired a wide spectrum of uses of nanodimensional materials ranging from industrial sector to biomedical applications. Inorganic nanomaterials made of noble metals, which are corrosion-resistant, are often included as electrode modifiers in designing electrochemical chemosensors and biosensors because of their unique catalytic, electric, and surface-related properties. This review summarizes the developments in electrochemical biosensors with integrated in their architecture metal nanostructures reported mainly during the last two years with a summary on some of the commonly used methods for the synthesis of metallic nanostructures. Nanodimensional noble metal structures might be considered as multipurpose electrode modifiers because of their abilities to act at the same time as electrocatalysts, signal amplifiers, and tools for immobilization and spatial orientation of redox proteins/enzymes or other type of bioreceptors.

Uniform, Scalable, High-Temperature Microwave Shock for Nanoparticle Synthesis through Defect Engineering

Summary Here we demonstrate a thermal shock synthesis method triggered by microwave irradiation for the rapid synthesis of nanoparticles on reduced graphene oxide (RGO) substrate. With properly controlled reduction, RGO has high electrical conductivity while maintaining functional groups, leading to an extremely efficient microwave absorption of ∼70%. The high utilization of microwaves results in the ability to raise the temperature to 1,600 K in just 100 ms, which is followed by rapid quenching to room temperature. The defects on the RGO are crucial for achieving this record-high microwave-induced temperature as these defects play a fundamental role in absorbing the radiation as well as the self-quenching mechanism. By loading precursors onto RGO, we can utilize rapid temperature change to synthesize nanoparticles. The nanoparticles are ∼10 nm with uniform distribution. This facile, rapid, and universal synthesis technique has the potential to be employed in large-scale production of nanomaterials and suggests a new direction for nanosynthesis.

Reduced graphene oxide supported palladium nano-shapes for electro-oxidation of oxalic acid

Size & shape controlled synthesis of metal nanoparticles are of high importance in catalysis. Colloidal techniques offer fine tunings in synthesis process as it involve multiple steps and reaction parameters. An efficient way of producing morphology controlled palladium nanostructures viz. palladium nanocubes (Pd-nc), palladium nanoicosahedrons (Pd-nico) supported on reduced graphene oxide (rGO) and its application in electro-catalysis is reported here. These Pd nano-shapes were achieved via sequential chemical reduction of Pd metal precursor and graphene oxide in the presence of reductant, ethylene glycol (EG) and stabilizer (capping agent), polyvinylpyrrolidone (PVP). Potassium bromide (KBr) and ascorbic acid (AA) were used as structure directing and secondary reducing agents respectively, to tune the geometry of Pd nanoparticles (Pd NPs). The preparation steps were optimized to yield cube shaped Pd nanoparticles (Pd-nc) with mean diameter of 4nm in the presence of KBr/AA; while in their absence, icosahedron shaped Pd nanoparticles (Pd-nico) with mean diameter of 3.1nm were formed and then homogeneously distributed over rGO sheets as evidenced by SEM-EDX and TEM. Further, Pd-nc/rGO and Pd-nico/rGO hybrid composite materials were used to investigate the electrochemical oxidation of oxalic acid (OA) in acidic medium. The results reveal that, these optimal size ranged nanostructures exhibit enhanced electro-catalytic activity when compared to bare glassy carbon electrode (GCE), towards OA oxidation. Among the two, Pd-nico/rGO showed enhanced activity than Pd-nc/rGO. The activity difference was justified based on the particle size distribution and no of surface exposed sites. The synthesis approach provides a versatile route for morphology (shape and size) controlled synthesis of metal nanostructures immobilized on support materials aiming towards fabrication of low cost composites in electro-catalysis and potential sensor applications.

Dynamics of 3D-island growth on weakly-interacting substrates

The growth dynamics of faceted three-dimensional (3D) Ag islands on weakly-interacting substrates are investigated—using kinetic Monte Carlo (kMC) simulations and analytical modelling—with the objective of determining the critical top-layer radius Rc required to nucleate a new island layer as a function of temperature T, at a constant deposition rate. kMC shows that Rc decreases from 17.3 to 6.0 Å as T is increased at 25 K intervals, from 300 to 500 K. That is, a higher T promotes top-layer nucleation resulting in an increase in island height-to-radius aspect ratios. This explains experimental observations for film growth on weakly-interacting substrates, which are not consistent with classical homoepitaxial growth theory. In the latter case, higher temperatures yield lower top-layer nucleation rates and lead to a decrease in island aspect ratios. The kMC simulation results are corroborated by an analytical mean field model, in which Rc is estimated by calculating the steady-state adatom density on the island side facets and top layer as a function of T. The overall findings of this study constitute a first step toward developing rigorous theoretical models, which can be used to guide synthesis of metal nanostructures, and layers with controlled shape and morphology, on technologically important substrates, including two-dimensional crystals, for nanoelectronic and catalytic applications.

Organic ligand-free PtIr alloy nanostructures for superior oxygen reduction and evolution reactions

In the thermal decomposition method, organic solvents, ligands, and compounds are usually used under an N2 atmosphere to synthesize pure metal and alloy nanostructures with high specific surface areas. However, the organic materials, which are used during the synthesis of metallic nanostructures, need to be completely eliminated to obtain cleaned surface states for effective catalytic reactions in aqueous atmospheres. Herein, we synthesize PtIr nanostructures using a thermal decomposition method, followed by a heating process of the nanostructures under an air atmosphere to eliminate the organic materials covering the surface of PtIr catalysts. The heated PtIr alloy nanostructure catalysts represent the superior oxygen reduction and evolution performance due to an increased electrochemical active surface area caused by the complete removal of organic materials.