Cobalt Nanosized Particles Organized in a 2D Superlattice: Synthesis, Characterization, and Magnetic Properties

Phase Control in Monometallic and Alloy Nanomaterials

Metal nanomaterials with unconventional phases have been recently developed with a variety of methods and exhibit novel and attractive properties such as high activities for various catalytic reactions and magnetic properties. In this review, we discuss the progress and the trends in strategies for synthesis, crystal structure, and properties of phase-controlled metal nanomaterials in terms of elements and the combination of alloys. We begin with a brief introduction of the anomalous phase behavior derived from the nanosize effect and general crystal structures observed in metal nanomaterials. Then, phase control in monometallic nanomaterials with respect to each element and alloy nanomaterials classified into three types based on their crystal structures is discussed. In the end, all the content introduced in this review is summarized, and challenges for advanced phase control are discussed.

In Situ TEM Characterization and Modulation for Phase Engineering of Nanomaterials

Solid-state phase transformation is an intriguing phenomenon in crystalline or noncrystalline solids due to the distinct physical and chemical properties that can be obtained and modified by phase engineering. Compared to bulk solids, nanomaterials exhibit enhanced capability for phase engineering due to their small sizes and high surface-to-volume ratios, facilitating various emerging applications. To establish a comprehensive atomistic understanding of phase engineering, in situ transmission electron microscopy (TEM) techniques have emerged as powerful tools, providing unprecedented atomic-resolution imaging, multiple characterization and stimulation mechanisms, and real-time integrations with various external fields. In this Review, we present a comprehensive overview of recent advances in in situ TEM studies to characterize and modulate nanomaterials for phase transformations under different stimuli, including mechanical, thermal, electrical, environmental, optical, and magnetic factors. We briefly introduce crystalline structures and polymorphism and then summarize phase stability and phase transformation models. The advanced experimental setups of in situ techniques are outlined and the advantages of in situ TEM phase engineering are highlighted, as demonstrated via several representative examples. Besides, the distinctive properties that can be obtained from in situ phase engineering are presented. Finally, current challenges and future research opportunities, along with their potential applications, are suggested.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Nanotoxicity of multifunctional stoichiometric cobalt oxide nanoparticles (SCoONPs) with repercussions toward apoptosis, necrosis, and cancer necrosis factor (TNF-α) at nano-biointerfaces

Introduction

Apoptosis, necrosis, and cancer necrosis factor (TNF-a) are all impacted by the nanotoxicity of multifunctional stoichiometric cobalt oxide nanoparticles (SCoONPs) at nano-biointerfaces. The creation of multi-functional nanoparticles has had a considerable impact on the transport of drugs and genes, nanotheranostics (in-vivo imaging, concurrent diagnostics), interventions for external healing, the creation of nano-bio interfaces, and the instigation of desired changes in nanotherapeutics.

Objectives

The quantitative structure-activity relationships, chemical transformations, biological interactions as well as toxicological analyses are considered as main objectives. Discrete dimensions of SCoNPs-cell interaction interfaces, their characteristic physical features (size, shape, shell structure, and surface chemistry), impact on cell proliferation and differentiation are the key factors responsible for nanotoxicity.

Methods

The development of multi-functional nanoparticles has been significant in drug/gene delivery, nanotheranostics (in-vivo imaging, coinciding diagnostics), and external healing interventions, designing a nano-bio interface, as well as inciting desired alterations in nanotherapeutics. Every so often, the cellular uptake of multi-functional cobalt [Co, CoO, Co2(CO)8 and Co3O4] nanoparticles (SCoONPs) influences cellular mechanics and initiates numerous repercussions (oxidative stress, DNA damage, cytogenotoxicity, and chromosomal damage) in pathways, including the generation of dysregulating factors involved in biochemical transformations.

Results

The concerns and influences of multifunctional SCoNPs on different cell mechanisms (mitochondria impermeability, hydrolysis of ATP, the concentration of Ca2+, impaired calcium clearance, defective autophagy, apoptosis, and necrosis), and interlinked properties (adhesion, motility, and internalization dynamics, role in toxicity, surface hydrophilic and hydrophobicity, biokinetics and biomimetic behaviors of biochemical reactions) have also been summarized. SCoONPs have received a lot of interest among the nanocarriers family because of its advantageous qualities such as biodegradability, biocompatibility, nontoxicity, and nonimmunogenicity.

Conclusion

Various applications, such as bio-imaging, cell labeling, gene delivery, enhanced chemical stability, and increased biocompatibility, concerning apoptosis, necrosis, and nano-bio interfaces, along with suitable examples. In this analysis, the multi-functional cobalt [Co, CoO, Co2(CO)8 and Co3O4] nanoparticles (SCoNPs) intricacies (cytogenotoxicity, clastogenicity, and immunomodulatory), nanotoxicity, and associated repercussions have been highlighted and explained.

Recent Advances in the Development of Drug Delivery Applications of Magnetic Nanomaterials

With the predicted rise in the incidence of cancer, there is an ever-growing need for new cancer treatment strategies. Recently, magnetic nanoparticles have stood out as promising nanostructures for imaging and drug delivery systems as they possess unique properties. Moreover, magnetic nanomaterials functionalized with other compounds can lead to multicomponent nanoparticles with innovative structures and synergetic performance. The incorporation of chemotherapeutic drugs or RNA in magnetic drug delivery systems represents a promising alternative that can increase efficiency and reduce the side effects of anticancer therapy. This review presents a critical overview of the recent literature concerning the advancements in the field of magnetic nanoparticles used in drug delivery, with a focus on their classification, characteristics, synthesis and functionalization methods, limitations, and examples of magnetic drug delivery systems incorporating chemotherapeutics or RNA.

Van der Waals Epitaxy Growth of 2D Single-Element Room-Temperature Ferromagnet

2D single-element materials, which are pure and intrinsically homogeneous on the nanometer scale, can cut the time-consuming material-optimization process and circumvent the impure phase, bringing about opportunities to explore new physics and applications. Herein, for the first time, the synthesis of ultrathin cobalt single-crystalline nanosheets with a sub-millimeter scale via van der Waals epitaxy is demonstrated. The thickness can be as low as ≈6 nm. Theoretical calculations reveal their intrinsic ferromagnetic nature and epitaxial mechanism: that is, the synergistic effect between van der Waals interactions and surface energy minimization dominates the growth process. Cobalt nanosheets exhibit ultrahigh blocking temperatures above 710 K and in-plane magnetic anisotropy. Electrical transport measurements further reveal that cobalt nanosheets have significant magnetoresistance (MR) effect, and can realize a unique coexistence of positive MR and negative MR under different magnetic field configurations, which can be attributed to the competition and cooperation effect among ferromagnetic interaction, orbital scattering, and electronic correlation. These results provide a valuable case for synthesizing 2D elementary metal crystals with pure phase and room-temperature ferromagnetism and pave the way for investigating new physics and related applications in spintronics.

Magnetic Nanostructures: Rational Design and Fabrication Strategies toward Diverse Applications

In recent years, the continuous development of magnetic nanostructures (MNSs) has tremendously promoted both fundamental scientific research and technological applications. Different from the bulk magnet, the systematic engineering on MNSs has brought a great breakthrough in some emerging fields such as the construction of MNSs, the magnetism exploration of multidimensional MNSs, and their potential translational applications. In this review, we give a detailed description of the synthetic strategies of MNSs based on the fundamental features and application potential of MNSs and discuss the recent progress of MNSs in the fields of nanomedicines, advanced nanobiotechnology, catalysis, and electromagnetic wave adsorption (EMWA), aiming to provide guidance for fabrication strategies of MNSs toward diverse applications.

Hybrids of Pd Nanoparticles and Metal-Organic Frameworks for Enhanced Magnetism

Nonmagnetic Pd exhibits ferromagnetism in the nanosize regime. Various stabilization agents, including surfactants, metal oxide supports, polymers, and porous materials (e.g., metal-organic frameworks (MOFs)), have been employed to prevent the agglomeration of metal nanoparticles. However, magnetic properties are greatly affected by the structural and electronic changes imposed by these stabilizing agents. In particular, metal-MOF hybrids (NPs@MOFs) have reduced magnetic properties, as reported by several authors. Herein, we report the enhancement in magnetic properties resulting from the combination of magnetic Pd NPs with UiO-66(Hf), which exhibits ferromagnetism, and the corresponding modifications in the hybridized structures. These hybridized structures are found to be strongly ferromagnetic, showing high magnetization and coercivity. We observed that the magnetic property is enhanced by 2 to 3 times upon including the Pd NPs on the surface of a UiO-66(Hf) shell support. For a fundamental understanding, the magnetization (M-H data) of the hybridized structure is analyzed with a modified Langevin function.

Recent Advances in Applications of Co-B Catalysts in NaBH4-Based Portable Hydrogen Generators

This review highlights the opportunities of catalytic hydrolysis of NaBH4 with the use of inexpensive and active Co-B catalysts among the other systems of hydrogen storage and generation based on water reactive materials. This process is important for the creation of H2 generators required for the operation of portable compact power devices based on low-temperature proton exchange membrane fuel cells (LT PEM FC). Special attention is paid to the influence of the reaction medium on the formation of active state of Co-B catalysts and the problem of their deactivation in NaBH4 solution stabilized by alkali. The novelty of this review consists in the discussion of basic designs of hydrogen generators based on NaBH4 hydrolysis using cobalt catalysts and the challenges of their integration with LT PEM FC. The potential of using batch reactors in which there is no need to use aggressive alkaline NaBH4 solutions is discussed. Solid-phase compositions or pellets based on NaBH4 and cobalt-containing catalytic additives are proposed, the hydrogen generation from which starts immediately after the addition of water. The review made it possible to formulate the most acute problems, which require new sci-tech solutions.

Quasi-Epitaxial Growth of Magnetic Nanostructures on 4H-Au Nanoribbons

Phase engineering of nanomaterials is an effective strategy to tune the physicochemical properties of nanomaterials for various promising applications. Herein, by using the 4H-Au nanoribbons as templates, four novel magnetic nanostructures, namely 4H-Au @ 14H-Co nanobranches, 4H-Au @ 14H-Co nanoribbons, 4H-Au @ 2H-Co nanoribbons, and 4H-Au @ 2H-Ni nanoribbons, are synthesized based on the quasi-epitaxial growth. Different from the conventional epitaxial growth of metal nanomaterials, the obtained Co and Ni nanostructures possess different crystal phases from the Au template. Due to the large lattice mismatch between Au and the grown metals (i.e., Co and Ni), ordered misfit dislocations are generated at the Co/Au and Ni/Au interfaces. Notably, a new super-structure of Co is formed, denoted as 14H. Both 4H-Au @ 14H-Co nanobranches and nanoribbons are ferromagnetic at room temperature, showing similar Curie temperature. However, their magnetic behaviors exhibit distinct temperature dependence, resulting from the competition between spin and volume fluctuations as well as the unique geometry. This work paves the way to the templated synthesis of nanomaterials with unconventional crystal phases for the exploration of phase-dependent properties.

Unraveling the mechanism of the one-pot synthesis of exchange coupled Co-based nano-heterostructures with a high energy product

The development of reproducible protocols to synthesize hard/soft nano-heterostructures (NHSs) with tailored magnetic properties is a crucial step to define their potential application in a variety of technological areas. Thermal decomposition has proved to be an effective tool to prepare such systems, but it has been scarcely used so far for the synthesis of Co-based metal/ferrite NHSs, despite their intriguing physical properties. We found a new approach to prepare this kind of nanomaterial based on a simple one-pot thermal decomposition reaction of metal-oleate precursors in the high boiling solvent docosane. The obtained NHSs are characterized by the coexistence of Co metal and Co doped magnetite and are highly stable in an air atmosphere, thanks to the passivation of the metal with a very thin oxide layer. The investigation of the influence of the metal precursor composition (a mixed iron-cobalt oleate), of the ligands (oleic acid and sodium oleate) and of the reaction time on the chemical and structural characteristics of the final product, allowed us to rationalize the reaction pathway and to determine the role of each parameter. In particular, the use of sodium oleate is crucial to obtain a metal phase in the NHSs. In such a way, the one-pot approach proposed here allows the fine control of the synthesis, leading to the formation of stable, high performant, metal/ferrite NHSs with tailored magnetic properties. For instance, the room temperature maximum energy product was increased up to 19 kJ m^-3 by tuning the Co content in the metal precursor.

Magnetic Field-Induced Assembly of Superparamagnetic Cobalt Nanoparticles on Substrates and at Liquid-Air Interface

Superparamagnetic cobalt nanoparticles (Co NPs) are an interesting material for self-assembly processes because of their magnetic properties. We investigated the magnetic field-induced assembly of superparamagnetic cobalt nanoparticles and compared three different approaches, namely, the assembly on solid substrates, at water-air, and ethylene glycol-air interfaces. Oleic acid- and trioctylphosphine oxide-coated Co NPs were synthesized via a thermolysis of cobalt carbonyl and dispersed into either hexane or toluene. The Co NP dispersion was dropped onto different substrates (e.g., transmission electron microscopy (TEM) grid, silicon wafer) and onto liquid surfaces. Transmission electron microscopy (TEM), scanning force microscopy, optical microscopy, as well as scanning electron microscopy showed that superparamagnetic Co NPs assembled into one-dimensional chains in an external magnetic field. By varying the concentration of the Co NP dispersion (1-5 mg/mL) and the strength of the magnetic field (4-54 mT), the morphology of the chains changed. Short, thin, and flexible chain structures were obtained at low NP concentration and low strength of magnetic field, whereas they became long, thick and straight when the NP concentration and the magnetic field strength increased. In comparison, the assembly of Co NPs from hexane dispersion at ethylene glycol-air interface showed the most regular and homogeneous alignment, since a more efficient spreading could be achieved on ethylene glycol than on water and solid substrates.

Self-Assembly of Quantum Dot-Gold Heterodimer Nanocrystals with Orientational Order

The self-assembly of nanocrystals into ordered superlattices is a powerful strategy for the production of functional nanomaterials. The assembly of well-ordered target structures, however, requires control over the building blocks' size and shape as well as their interactions. While nanocrystals with homogeneous composition are now routinely synthesized with high precision and assembled into various ordered structures, high-quality multicomponent nanocrystals and their ordered assemblies are rarely reported. In this paper, we demonstrate the synthesis of quantum dot-gold (QD-Au) heterodimers. These heterodimers possess a uniform shape and narrow size distribution and are capped with oleylamine and dodecyltrimethylammonium bromide (DTAB). Assembly of the heterodimers results in a superlattice with long-range orientational alignment of dimers. Using synchrotron-based X-ray measurements, we characterize the complex superstructure formed from the dimers. Molecular dynamics simulations of a coarse-grained model suggest that anisotropic interactions between the quantum dot and gold components of the dimer drive superlattice formation. The high degree of orientational order demonstrated in this work is a potential route to nanomaterials with useful optoelectronic properties.

Syntheses and Properties of Metal Nanomaterials with Novel Crystal Phases

In recent decades, researchers have devoted tremendous effort into the rational design and controlled synthesis of metal nanomaterials with well-defined size, morphology, composition, and structure, and great achievements have been reached. However, the crystal-phase engineering of metal nanomaterials still remains a big challenge. Recent research has revealed that the crystal phase of metal nanomaterials can significantly alter their properties, arising from the distinct atomic arrangement and modified electronic structure. Until now, it has been relatively uncommon to synthesize metal nanomaterials with novel crystal phases in spite of the fact that these nanostructures would be promising for various applications. Here, the research progress regarding the fine control of noble metal (Au, Ag, Ru, Rh, Pd) and non-noble metal (Fe, Co, Ni) nanomaterials with novel crystal phases is reviewed. First, synthesis strategies and their phase transformations are summarized, while highlighting the peculiar characteristics of each element. The phase-dependent properties are then discussed by providing representative examples. Finally, the challenges and perspectives in this emerging field are proposed.

Magnetic Nano-Сomposites and their Industrial Applications

Magnetic nanocomposites are multi-component, nanosized magnetic materials, to generate the response to an external stimulus (i.e., outer inert or alternative magnetic field). The novel nanocomposites is a combination of excess of various materials such as liquid crystals, silica, gels, renewable polymers, carbon along with different magnetic particles. They have immense applications in the field of medical diagnosis and therapy, catalysis and separation. These nanocarriers are mainly classified into nanotubes, nanosheets, spherical nanoparticles, nanofibres, highly porous nanocomposites. The porous nanostructures provides a better surface for the entrapment or covalent binding of enzymes, proteins, biomolecules and drugs but the major challenge is to design and synthesize a desired structure with suitable surface properties and biocompatibility. Extensive attempts have been made to manipulate the mesoporous materials and its combination with other structure in order to synthesize a matrix with appropriate pore size, large surface area to volume ratio. “Bottom-up” and “Bottom-down” chemical-based synthesis methods have been widely employed to prepare magnetic nanoparticles. Magnetic nanocomposites are synthesized from magnetic nanoparticles and biopolymers by using sol-gel technique, chemical precipitation methods and NanogenTM, a microwave plasma method. In this chapter, we described the advances and developments in the formation/synthesis of magnetic nanocomposites. This chapter will review the characteristics, properties and applications of the magnetic nanocomposites.

Magneto-plasmonic Au-Coated Co nanoparticles synthesized via hot-injection method

A synthetic procedure is described for the obtaining of superparamagnetic Co nanoparticles (NPs) via hot-injection method in the presence of sodium borohydride. The Co NPs obtained have an average diameter of 5.3 nm and saturation magnetization of 115 emu g^-1. A modified Langevin equation is fitted to the magnetization curves using a log-normal distribution for the particle diameter and an effective field to account for dipolar interactions. The calculated magnetic diameter of the Co NPs is 0.6 nm smaller than TEM-derived values, implying a magnetic dead layer of 0.3 nm. The magnetic core is coated with Au to prevent oxidation, resulting in water-stable magneto-plasmonic Co/Au core/shell NPs with saturation of 71.6 emu g^-1. The coating adds a localized surface plasmon resonance property with absorbance in the so-called 'therapeutic window' (690-900 nm), suitable for biomedical applications. It is suggested that these multifunctional NPs are distinguished as a potential platform for applied and fundamental research.

SLADS: a parallel code for direct simulations of scattering of large anisotropic dense nanoparticle systems

SLADS(http://www.pims.ac.cn/Resources.html), a parallel code for direct simulations of X-ray scattering of large anisotropic dense nanoparticle systems of arbitrary species and atomic configurations, is presented. Particles can be of arbitrary shapes and dispersities, and interactions between particles are considered. Parallelization is achieved in real space for the sake of memory limitation. The system sizes attempted are up to one billion atoms, and particle concentrations in dense systems up to 0.36. Anisotropy is explored in terms of superlattices. One- and two-dimensional small-angle scattering or diffraction patterns are obtained.SLADSis validated self-consistently or against cases with analytical solutions.

Organic Phase Syntheses of Magnetic Nanoparticles and Their Applications

In the past two decades, the synthetic development of magnetic nanoparticles (NPs) has been intensively explored for both fundamental scientific research and technological applications. Different from the bulk magnet, magnetic NPs exhibit unique magnetism, which enables the tuning of their magnetism by systematic nanoscale engineering. In this review, we first briefly discuss the fundamental features of magnetic NPs. We then summarize the synthesis of various magnetic NPs, including magnetic metal, metallic alloy, metal oxide, and multifunctional NPs. We focus on the organic phase syntheses of magnetic NPs with precise control over their sizes, shapes, compositions, and structures. Finally we discuss the applications of various magnetic NPs in sensitive diagnostics and therapeutics, high-density magnetic data recording and energy storage, as well as in highly efficient catalysis.

From cage-in-cage MOF to N-doped and Co-nanoparticle-embedded carbon for oxygen reduction reaction

By pyrolysis of “cage-in-cage” MOF, nitrogen-doped carbon embedded Co nanoparticles were obtained and they showed efficient electrochemical activity for oxygen reduction.

Preparation and catalytic applications of nanomaterials: a review

The present review systematically summarizes the synthesis and specific catalytic applications of nanomaterials such as MSN, nanoparticles, LD hydroxides, nanobubbles, quantum dots,etc.

Controlled deposition of magnetic particles within the 3-D template of wood: making use of the natural hierarchical structure of wood

Process of modifying wood veneer samples with metal salts to result in magnetic particle modified wood and images of the cross section of a wood sample lumen cell wall unmodified and modified with the deposition of magnetic particles.

Effect of the different synthetic parameters on the morphology and magnetic properties of nickel nanoparticles

The morphology of stable spherical Ni(0) nanoparticles can be modified to obtain flower-like Ni(0) arrangements by reheating them, retaining their high crystallinity and without oxidation of the nanoparticles.

A review on radiation-induced nucleation and growth of colloidal metallic nanoparticles

This review presents an introduction to the synthesis of metallic nanoparticles by radiation-induced method, especially gamma irradiation. This method offers some benefits over the conventional methods because it provides fully reduced and highly pure nanoparticles free from by-products or chemical reducing agents, and is capable of controlling the particle size and structure. The nucleation and growth mechanism of metallic nanoparticles are also discussed. The competition between nucleation and growth process in the formation of nanoparticles can determine the size of nanoparticles which is influenced by certain parameters such as the choice of solvents and stabilizer, the precursor to stabilizer ratio, pH during synthesis, and absorbed dose.

Clusters and lattices of particles stabilized by dipolar coupling

We model stabilization of clusters and lattices of spherical particles with dominant electric and magnetic dipolar coupling, and weak van der Waals coupling. Our analytical results demonstrate that dipolar coupling can stabilize nanoparticle clusters with planar, tubular, Möbius, and other arrangements. We also explain for which parameters the nanoparticles can form lattices with fcc, hcp, sh, sc, and other types of packing. Although these results are valid at different scales, we illustrate that realistic magnetic and semiconducting nanoparticles need to have certain minimum sizes to stabilize at room temperature into nanostructures controlled by dipolar coupling.