0,1,2,3D nanostructures, types of bulk nanostructured materials, and drug nanocrystals: An overview.

Functional materials are required to meet the needs of society, such as environmental protection, energy storage and conversion, integrated product production, biological and medical processing. bulk nanostructured materials are a research concept that combines nanotechnology with other research fields such as supramolecular chemistry, materials science, and life science to develop logically functional materials from nanodevices. In this review article, nanostructures are synthetized by different methods based on the types and nature of the nanomaterials. In a broad sense "top-down" and "bottom-up" are the two foremost methods to synthesize nanomaterials. In top-down method bulk materials have been reduced to nanomaterials, and in case of bottom-up method, the nanomaterials are synthesized from elementary level. The different methods which are being used to synthesize nanomaterials are chemical vapor deposition method, thermal decomposition, hydrothermal synthesis, solvothermal method, pulsed laser ablation, templating method, combustion method, microwave synthesis, gas phase method, and conventional Sol-Gel method. We also briefly discuss the various physical and chemical methods for producing nanomaterials. We then discuss the applications of functional materials in many areas such as energy storage, supercapacitors, sensors, wastewater treatment, and other biological applications such as drug delivery and drug nanocrystals. Finally, future challenges in materials nanoarchitecture and concepts for further development of functional nanomaterials are briefly discussed.

Triple Junction Segregation Dominates the Stability of Nanocrystalline Alloys.

We present large-scale atomistic simulations that reveal triple junction (TJ) segregation in Pt-Au nanocrystalline alloys in agreement with experimental observations. While existing studies suggest grain boundary solute segregation as a route to thermally stabilize nanocrystalline materials with respect to grain coarsening, here we quantitatively show that it is specifically the segregation to TJs that dominates the observed stability of these alloys. Our results reveal that doping the TJs renders them immobile, thereby locking the grain boundary network and hindering its evolution. In dilute alloys, it is shown that grain boundary and TJ segregation are not as effective in mitigating grain coarsening, as the solute content is not sufficient to dope and pin all grain boundaries and TJs. Our work highlights the need to account for TJ segregation effects in order to understand and predict the evolution of nanocrystalline alloys under extreme environments.

Lattice variation as a function of concentration and grain size in MgO-NiO solid solution system.

The study aimed to understand how changes in crystal's size affect the lattice parameters and crystal structure of Mg1-xNixO solid solution for six X values ranging from x = 0 to x = 1. Mg1-xNixO was synthesized via two different wet-chemical techniques: the sol-gel and the microwave hydrothermal method, both followed by calcination at different temperatures of 673, 873, 1073, 1273 and 1473 K. As annealing caused grain growth, the varied temperature range allowed to examine a wide range of grain sizes. The lattice parameters and x values were determined from XRD (X-ray diffraction) peak positions and intensities respectively. The grain size was evaluated by XRD line profile analysis and supported by SEM (scanning electron microscope) observations. At the temperatures of 673 and 873 K grain size was in the nanometric range and from 1073 K and above grain size was in the micrometric range. A non-monotonic lattice variation versus grain size was found for each concentration. When grain size decreased there was a slight contraction, however for grain size in the nanometric range there was a severe lattice expansion. Both lattice parameter changes were explained by two effects acting together: contraction due to surface stress and expansion due to weakening of the ionic bonding at nanocrystalline particles. In this current research study, the lattice parameter was mapped in two dimensions: concentration and grain size. The findings of this study provided valuable insights into the lattice variation in the MgO-NiO solid solution system.

Ultrahigh Permeability at High Frequencies via A Magnetic-Heterogeneous Nanocrystallization Mechanism in an Iron-Based Amorphous Alloy.

The prevalence of wide-bandgap (WBG) semiconductors allows modern electronic devices to operate at much higher frequencies. However, development of soft magnetic materials with high-frequency properties matching the WBG-based devices remains challenging. Here, a promising nanocrystalline-amorphous composite alloy with a normal composition Fe75.5 Co0.5 Mo0.5 Cu1 Nb1.5 Si13 B8 in atomic percent is reported, which is producible under industrial conditions, and which shows an exceptionally high permeability at high frequencies up to 36 000 at 100 kHz, an increase of 44% compared with commercial FeSiBCuNb nanocrystalline alloy (25 000 ± 2000 at 100 kHz), outperforming all existing nanocrystalline alloy systems and commercial soft magnetic materials. The alloy is obtained by a unique magnetic-heterogeneous nanocrystallization mechanism in an iron-based amorphous alloy, which is different from the traditional strategy of nanocrystallization by doping nonmagnetic elements (e.g., Cu and Nb). The induced magnetic inhomogeneity by adding Co atoms locally promotes the formation of highly ordered structures acting as the nuclei of nanocrystals, and Mo atoms agglomerate around the interfaces of the nanocrystals, inhibiting nanocrystal growth, resulting in an ultrafine nanocrystalline-amorphous dual-phase structure in the alloy. The exceptional soft magnetic properties are shown to be closely related to the low magnetic anisotropy and the unique spin rotation mechanism under alternating magnetic fields.

Experiments push the limits of micromagnetic SANS theory.

Commentary is provided on recent magnetic SANS experiments on highly inhomogeneous high-pressure-torsion manufactured metals. The ensuing progress in the theoretical description of magnetic SANS using micromagnetic theory is highlighted.

Effect of annealing on the magnetic microstructure of high-pressure torsion iron: the relevance of higher-order contributions to the magnetic small-angle neutron scattering cross section.

The development of higher-order micromagnetic small-angle neutron scattering theory in nanocrystalline materials is still in its infancy. One key challenge remaining in this field is understanding the role played by the microstructure on the magnitude and sign of the higher-order scattering contribution recently observed in nanocrystalline materials prepared by high-pressure torsion. By combining structural and magnetic characterization techniques, namely X-ray diffraction, electron backscattered diffraction and magnetometry with magnetic small-angle neutron scattering, this work discusses the relevance of higher-order terms in the magnetic small-angle neutron scattering cross section of pure iron prepared by high-pressure torsion associated with a post-annealing process. The structural analysis confirms: (i) the preparation of ultra-fine-grained pure iron with a crystallite size below 100 nm and (ii) rapid grain growth with increasing annealing temperature. The analysis of neutron data based on the micromagnetic small-angle neutron scattering theory extended to textured ferromagnets yields uniaxial magnetic anisotropy values that are larger than the magnetocrystalline value reported for bulk iron, supporting the existence of induced magnetoelastic anisotropy in the mechanically deformed samples. Furthermore, the neutron data analysis revealed unambiguously the presence of non-negligible higher-order scattering contributions in high-pressure torsion iron. Though the sign of the higher-order contribution might be related to the amplitude of the anisotropy inhomogeneities, its magnitude appears to be clearly correlated to the changes in the microstructure (density and/or shape of the defects) induced by combining high-pressure torsion and a post-annealing treatment.

A simple formula for determining nanoparticle size distribution by combining small-angle X-ray scattering and diffraction results.

X-ray scattering and diffraction phenomena are widely used as analytical tools in nanoscience. Size discrepancies between the two phenomena are commonly observed in crystalline nanoparticle systems. The root of the problem is that each phenomenon is affected by size distribution differently, causing contrasting shifts between the two methods. Once understood, the previously discrepant results lead to a simple formula for obtaining the nanoparticle size distribution.

A Simple Grinding Method for Preparing Ultra-Thin Boron Nanosheets.

The preparation of boron nanosheets has very strict requirements of the preparation environment and substrate. In this work, the boron nanosheets were tried to prepare by the grinding method, using ß-B alloy with stable chemical properties and large crystal plane spacing. Its morphology and chemical bonds of boron nanosheets were analyzed by scanning microscope (SEM), transmission microscope (TEM), and X-ray photoelectron spectroscopy (XPS). The results show that the two-dimensional boron nanosheets can be prepared from ß-B powder by the grinding method. There are very few B-O bonds in boron particles, and the B-B bonds are principally dominant. In addition to a few B-O bonds, including some B-B bonds change to B6O bonds which are not completely oxidized, indicating that boron has certain oxidation resistance.

Al13Fe4-Al Composites with Nanocrystalline Matrix Manufactured by Hot-Pressing of Milled Powders.

The paper describes composites with the matrix containing a nanocrystalline intermetallic Al13Fe4 phase and microcrystalline aluminium. Mechanically alloyed Al80Fe20 powder, containing a metastable nanocrystalline Al5Fe2 phase, was mixed with 20, 30, and 40 vol.% of Al powder and consolidated at 750 °C under the pressure of 7.7 GPa. During the consolidation, the metastable Al5Fe2 phase transformed into a nanocrystalline Al13Fe4 phase. In the bulk samples, Al13Fe4 areas were wrapped around by networking Al regions. The hardness of the Al13Fe4-Al composites was in the range of 4.52-5.50 GPa. The compressive strength of the Al13Fe4-30%Al and Al13Fe4-40%Al composites was 805 and 812 MPa, respectively, and it was considerably higher than that of the Al13Fe4-20%Al composite (538 MPa), which failed in the elastic region. The Al13Fe4-30%Al and Al13Fe4-40%Al composites, in contrast, showed some plasticity: namely, 1.5% and 9.1%, respectively. The density of the produced composites is in the range of 3.27-3.48 g/cm3 and decreases with the increase in the Al content.

Corrosion Behavior of Ultrafine-Grained CoCrFeMnNi High-Entropy Alloys Fabricated by High-Pressure Torsion.

The influence of the nanocrystalline structure produced by severe plastic deformation (SPD) on the corrosion behavior of CoCrFeMnNi alloys with Cr contents ranging from 0 to 20 at.% was investigated in aqueous 0.5 M H2SO4 and 3.5% NaCl solutions. The resistance to general corrosion and pitting became higher in both the solutions, with higher passivation capability observed with increasing Cr content, and it is believed that the high corrosion resistance of CoCrFeMnNi alloys can be attributed to the incorporation of the Cr element. However, the impact of the nanocrystalline structure produced by SPD on the corrosion behavior was negligibly small. This is inconsistent with reports on nanocrystalline binary Fe-Cr alloys and stainless steels processed by SPD, where grain refinement by SPD results in higher corrosion resistance. The small change in the corrosion behavior with respect to grain refinement is discussed, based on the passivation process of Fe-Cr alloys and on the influence of the core effects of HEAs on the passivation process.

Effect of Nanostructuring on the Thermoelectric Properties of ß-FeSi2.

Nanostructured ß-FeSi2 and ß-Fe0.95Co0.05Si2 specimens with a relative density of up to 95% were synthesized by combining a top-down approach and spark plasma sintering. The thermoelectric properties of a 50 nm crystallite size ß-FeSi2 sample were compared to those of an annealed one, and for the former a strong decrease in lattice thermal conductivity and an upshift of the maximum Seebeck's coefficient were shown, resulting in an improvement of the figure of merit by a factor of 1.7 at 670 K. For ß-Fe0.95Co0.05Si2, one observes that the figure of merit is increased by a factor of 1.2 at 723 K between long time annealed and nanostructured samples mainly due to an increase in the phonon scattering and an increase in the point defects. This results in both a decrease in the thermal conductivity to 3.95 W/mK at 330 K and an increase in the power factor to 0.63 mW/mK2 at 723 K.

Effect of borates on the synthesis of nanoscale hexagonal boron nitride by a solid-state method.

This study delves deeply into the effect of different borates (lithium tetraborate, sodium tetraborate, calcium metaborate, ammonium pentaborate) on the production and fundamental characteristic features of nanoscale hexagonal boron nitride (hBN) structure with the assistant of standard characteristic measurement methods, namely, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). The hBN samples are synthesized by reaction of powder urea, boron oxide, and different kinds of borates via the modified O'Connor method (performed at a relatively lower main heat treatment temperature of 1,100°C). All the results obtained show that the usage of borates affects positively the formation of nanoscale hBN structure. In more detail, the FTIR experiment results reveal that the presence of two strong c peaks appeared at ~1,380 and ~780 cm-1 in the spectra points out the conventional BN in-plane and out-of-plane vibrations, respectively. The XRD patterns also confirm the production of high-ordered hBN as the existence of the main peaks of the corresponding hexagonal system. As for the SEM examination, it is found that all the hBN materials exhibit totally different crystallinity quality and microstructural characteristics. The hBN compound prepared by the sodium tetraborate content shows the most uniform surface appearance with the smoothest/densest crystal structure, best grain orientations, and finest grain interactions. Hence, the material with strong stretching of interatomic bonds shows the highest material (fracture) strength. Moreover, the TEM images illustrate that all the products are composed of uniform multi-walled nanotubes and nanorods with an average length of ~250 nm.

The Role of the Surface Acid-Base Nature of Nanocrystalline Hydroxyapatite Catalysts in the 1,6-Hexanediol Conversion.

Hydroxyapatite is known to have excellent catalytic properties for ethanol conversion and lactic acid conversion, and their properties are influenced by the elemental composition, such as Ca/P ratio and sodium content. However, few reports have been examined for the surface acid-base nature of hydroxyapatites containing sodium ions. We prepared nanocrystalline hydroxyapatite (Ca-HAP) catalysts with various Ca/P ratios and sodium contents by the hydrothermal method. The adsorption and desorption experiments using NH3 and CO2 molecules and the catalytic reactions for 2-propenol conversion revealed that the surface acid-base natures changed continuously with the bulk Ca/P ratios. Furthermore, the new catalytic properties of hydroxyapatite were exhibited for 1,6-hexanediol conversion. The non-stoichiometric Ca-HAP(1.54) catalyst with sodium ions of 2.3 wt% and a Ca/P molar ratio of 1.54 gave a high 5-hexen-1-ol yield of 68%. In contrast, the Ca-HAP(1.72) catalyst, with a Ca/P molar ratio of 1.72, gave a high cyclopentanemethanol yield of 42%. Both yields were the highest ever reported in the relevant literature. It was shown that hydroxyapatite also has excellent catalytic properties for alkanediol conversion because the surface acid-base properties can be continuously controlled by the elemental compositions, such as bulk Ca/P ratios and sodium contents.

Nitriding and Denitriding of Nanocrystalline Iron System with Bimodal Crystallite Size Distribution.

An artificially prepared nanocrystalline iron sample with bimodal crystallite size distribution was nitrided and denitrided in the NH3/H2 atmosphere at 350 °C and 400 °C. The sample was a 1:1 mass ratio mixture of two iron samples with mean crystallite sizes of 48 nm and 21 nm. Phase transformations between α-Fe, γ'-Fe4N and ε-Fe3-2N were observed by the in situ X-ray powder diffraction method. At selected steps of nitriding or denitriding, phase transformations paused at 50% of mass conversion and resumed after prominent variation of the nitriding atmosphere. This effect was attributed to the separation of phase transformations occurring between sets of iron crystallites of 48 nm and 21 nm, respectively. This was due to the Gibbs-Thomson effect, which establishes the dependence of phase transformation conditions on crystallite sizes.

Enhanced cyclic performance initiated via an in situ transformation of Cu/CuO nanodisk to Cu/CuO/Cu2O nanosponge.

A simple oxidation method for preparing CuO nanodisks on a flexible Cu sheet is presented. The crystal structure of as-prepared CuO nanodisks was analyzed by X-ray diffraction. The elemental composition and surface morphology were documented by X-ray photoelectron spectroscopy, scanning, and transmission electron microscopy. The photocatalytic performance of flexible Cu/CuO nanodisks was tested to mediate the degradation of RhB and MB dyes. After 2nd recycling, an in situ transformation of the nanodisk surface leads to electron transfer between the conduction bands of Cu2O and CuO phase, accelerating the degradation of the dyes due to a more favorable electron-hole separation under different band gap engineering. The optical and electrochemical impedance analyses were conducted to examine the efficiency of photogenerated charge carrier separation. Additionally, in the photodegradation system of Cu/CuO nanodisks, the generation of superoxide radical (·O2-) is responsible for the dye degradation under daylight irradiation. The generation of the latter radical is energetically feasible since the conduction band of Cu2O (- 0.28 eV) is well-matching with the redox potential of O2/·O2- (- 0.28 eV). Consequently, it is concluded that the cyclic stability shows the usefulness of Cu/CuO nanodisk preparation for the dye degradation under daylight irradiation. Graphical abstract.

A 2.9 GPa Strength Nano-Grained and Nano-Precipitated 304L-Type Austenitic Stainless Steel.

Austenitic stainless steel has high potential as nuclear and engineering materials, but it is often coarse grained and has relatively low yield strength, typically 200-400 MPa. We prepared a bulk nanocrystalline lanthanum-doped 304L austenitic stainless steel alloy by a novel technique that combines mechanical alloying and high-pressure sintering. The achieved alloy has an average grain size of 30 ± 12 nm and contains a high density (~1024 m-3) of lanthanum-enriched nanoprecipitates with an average particle size of approx. 4 nm, leading to strong grain boundary strengthening and dispersion strengthening effects, respectively. The yield strength of nano-grained and nano-precipitated stainless steel reaches 2.9 GPa, which well exceeds that of ultrafine-grained (100-1000 nm) and nano-grained (<100 nm) stainless steels prepared by other techniques developed in recent decades. The strategy to combine nano-grain strengthening and nanoprecipitation strengthening should be generally applicable to developing other ultra-strong metallic alloys.

Mechanochemical Synthesis of Nanocrystalline Hydroxyapatite from Ca(H2PO4)2.H2O, CaO, Ca(OH)2, and P2O5 Mixtures.

This paper reports the progress of the mechanochemical synthesis of nanocrystalline hydroxyapatite (HA) starting from six different powder mixtures containing Ca(H2PO4)2.H2O, CaO, Ca(OH)2, and P2O5. The reaction kinetics of HA phase formation during high-energy ball milling was systematically investigated. The mechanochemical reaction rate of the Ca(H2PO4)2.H2O-Ca(OH)2 powder mixture found to be very fast as the HA phase started to form at around 2 min and finished after 30 min of ball milling. All six powder mixtures were transformed entirely into HA, with the crystallite size between 18.5 and 20.2 nm after 1 h and between 22.5 and 23.9 nm after 2 h of milling. Moreover, the lattice strain was found to be 0.8 ± 0.05% in the 1 h milled powder and 0.6 ± 0.05% in all six powders milled for 2 h. This observation, i.e., coarsening of the HA crystal and gradual decrease of the lattice strain with the increase of milling time, is opposite to the results reported by other researchers. The gradual increase in crystallite size and decrease in lattice strain result from dynamic recovery and recrystallization because of an increase in the local temperature of the powder particles trapped between the balls and ball and reactor wall during the high-energy collision.

Sol-Gel Synthesis of Nanocrystalline Mesoporous Li4Ti5O12 Thin-Films as Anodes for Li-Ion Microbatteries.

The development of anodes based on Li4Ti5O12 (LTO) for lithium ion batteries has become very important in recent years on the basis that it allows a long service life (stability in charge-discharge cycling) and safety improvements. The processing of this material in the form of thin film allows for greater control of its characteristics and an improvement of its disadvantages, namely reduced electrical conductivity and low diffusion of lithium ions. In this work, we try to limit these disadvantages through the synthesis of a mesostructured carbon-doped Li4Ti5O12 thin-film with a pure spinel phase using a combination of a block-copolymer template and in situ synthesis of Li-Ti double alkoxide. Structural and electrochemical characterization has been carried out to determine the best conditions (temperature, time, atmosphere) for the thermal treatment of the material to reach a compromise between crystallinity and porosity distribution (pore size, pore volume, and interconnectivity).

Coercivity and Magnetic Anisotropy of (Fe0.76Si0.09B0.10P0.05)97.5Nb2.0Cu0.5 Amorphous and Nanocrystalline Alloy Produced by Gas Atomization Process.

We present the evolution of magnetic anisotropy obtained from the magnetization curve of (Fe0.76Si0.09B0.10P0.05)97.5Nb2.0Cu0.5 amorphous and nanocrystalline alloy produced by a gas atomization process. The material obtained by this process is a powder exhibiting amorphous character in the as-atomized state. Heat treatment at 480 °C provokes structural relaxation, while annealing the powder at 530 °C for 30 and 60 min develops a fine nanocrystalline structure. Magnetic anisotropy distribution is explained by considering dipolar effects and the modified random anisotropy model.

Investigation into the Effect of Thermal Treatment on the Obtaining of Magnetic Phases: Fe5Y, Fe23B6, Y2Fe14B and αFe within the Amorphous Matrix of Rapidly-Quenched Fe61+xCo10-xW1Y8B20 Alloys (Where x = 0, 1 or 2).

The paper presents the results of research on the structure and magnetic properties of Fe61+xCo10-xW1Y8B20 alloys (where x = 0, 1 or 2). The alloys were produced using two production methods with similar cooling rates: Injection casting and suction casting. The alloy samples produced were subjected to isothermal annealing at 940 K for 10 min. The structure of the materials was examined using X-ray diffraction. Isothermal annealing has led to the formation of various crystallization products depending on the chemical composition of the alloy and the structure of the alloy in a solidified state. In two cases, the product of crystallization was the hard magnetic phase Y2Fe14B. However, the mechanism of this phase formation was different in both cases. The magnetic properties of alloys were tested using a vibrating sample magnetometer and a Faraday magnetic balance. It is found that the grain crystallite size of the crystalline phases have a decisive influence on the value of the coercive field (especially in the case of hard magnetic phases). It has been shown that privileged areas can already be created during the production process. Their presence determines the crystallization process.