Heterogeneous Nanostructures Research Articles

Metallic Heterostructures for Plasmon-Enhanced Electrocatalysis.

Metallic heterogeneous nanostructures with plasmonic functionality have attracted great attention in the field of plasmon-enhanced electrocatalysis, where surface plasmons produced under light excitation could facilitate the overall electrocatalytic performances. Owing to their controllability, multifunctionality, and complexity, heterogeneous metallic nanostructures take advantages of the properties from individual components and synergistic effects from adjacent components, thus may achieve remarkable electrocatalytic performances. This review highlights the state-of-the-art progress of the application of metallic heterostructures for plasmon-enhanced electrocatalysis. First, a brief introduction to plasmonic heterogeneous nanostructures is demonstrated. Then, fundamental principles of localized surface plasmon resonance and the underlying mechanisms of plasmonic heterogeneous nanostructures in catalysis are discussed. This is followed by a discussion of recent advances of plasmonic heterogeneous nanostructures in plasmon-enhanced electrocatalysis, in which the enhanced activity, selectivity, and stability are particularly emphasized. Finally, an outlook of remaining challenges and future opportunities for plasmonic heterogeneous nanomaterials and plasmon-related electrocatalysis is presented.

Hierarchical FeCoNiCr high entropy alloy thin films with combined high strength and excellent corrosion resistance

A two-step temperature-controlled magnetron sputtering procedure was adopted to obtain a bilayer hierarchical Fe25.2Co25.2Ni27.4Cr22.2 high entropy alloy (HEA) thin film consisting of the external nano-lamellar layer and internal equiaxed zone, which displayed combined advantages of high hardness, good modulus and excellent corrosion resistance. The roles of heterogeneous nanostructure on the mechanical and corrosion behavior were revealed by nano-indentation and Scanning Kelvin probe (SKP) methods. Compared to the substrate 304 ASS, the hierarchical HEA film not only shows much higher nano-hardness and modulus values, but also possesses a higher electron transfer resistance (12158 vs 4567 Ω.cm2) and lower overall corrosion rate (6.28*10−4 vs 6.84*10−3 mm·year−1). Moreover, the outer nano-lamellar layer shows higher nano-hardness (∼8.1 GPa) but lower surface potential values (∼-261 mV) than those of the inter equiaxed zone (∼5.9 GPa and ∼−150 mV). The former arises from the significant grain refinement strengthening effect, while the latter is attributed to an obvious increase in the high energy and chemically active areas such as grain boundaries and triple junctions. This work demonstrates the capability of hierarchy to adjust the comprehensive performance of multi-functional films, which possess superior mechanical property and comparable corrosion performance than those of the as-cast bulk HEA alloys.

Orientation-dependent plasticity mechanisms control synergistic property improvement in dynamically deformed metals

We demonstrate the ability to synergistically enhance strength and toughness in metals by tailoring the dominant plasticity mechanisms from impact-induced heterogeneous nanostructures. Using a laser-induced projectile impact testing apparatus, we impact initially dislocation-free single crystal microcubes at high velocities to induce grain size and dislocation density gradients. These gradient nanostructures exhibit heterogeneous deformation under subsequent quasi-static loading leading to enhanced strength and toughness. Transmission Kikuchi diffraction (TKD) analyses show that the synergistic property improvement arises from the complimentary intragranular and intergranular plasticity mechanisms: the pronounced intragranular dislocation plasticity within coarse grained regions provides increased strain hardening and toughness while the nanograined regions with high dislocation densities provide high strength and supplemental toughness enhancement through cooperative grain rotation and grain boundary migration. These plasticity mechanisms are activated to different extents depending on the specific impact-induced nanostructures, which depend on the orientation of the single crystal upon impact. Controlled [100]-face, [110]-edge, and [111]-corner impact of single crystal microcubes, subsequent quasi-static mechanical testing, and pre- and post-compression nanostructural characterization provide a fundamental understanding of the comprehensive process-structure-property relations in heterogeneous nanostructured metals.

CuAlO2/CuBi2O4 heterojunction photocathodes with improved charge collection for efficient solar water splitting

P-type heterojunction photoelectrode made of CuAlO2 and CuBi2O4 has been developed for the first time by using solution-based deposition method. Its advantageous bandgap size and favourable band positions make it a highly prospective option for photoelectrochemical (PEC) water splitting. The photoelectrode was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis absorption spectra, time-resolved photoluminescence (TRPL) and X-ray photoelectron spectroscopy (XPS). Compared to CuBi2O4 alone, the heterojunction photoelectrode showed improved photoelectrochemical activity with the highest photocurrent density of − 0.62 mA/cm2 at 0.6 V vs. RHE. The improvement is attributed to decreased recombination of photo-generated electrons and holes and improved charge separation and transport in the heterostructure. This research offers an efficient method to enhance the visible-light-driven activity of CuBi2O4 and a new strategy for fabricating heterogeneous nanostructure photoelectrodes for solar-driven water splitting.

Characterization and Behaviour of Silica Engineered Nanocontainers in Low and High Ionic Strength Media.

Mesoporous silica engineered nanomaterials are of interest to the industry due to their drug-carrier ability. Advances in coating technology include using mesoporous silica nanocontainers (SiNC) loaded with organic molecules as additives in protective coatings. The SiNC loaded with the biocide 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), i.e., SiNC-DCOIT, is proposed as an additive for antifouling marine paints. As the instability of nanomaterials in ionic-rich media has been reported and related to shifting key properties and its environmental fate, this study aims at understanding the behaviour of SiNC and SiNC-DCOIT in aqueous media with distinct ionic strengths. Both nanomaterials were dispersed in (i) low- (ultrapure water-UP) and (ii) high- ionic strength media-artificial seawater (ASW) and f/2 medium enriched in ASW (f/2 medium). The morphology, size and zeta potential (ζP) of both engineering nanomaterials were evaluated at different timepoints and concentrations. Results showed that both nanomaterials were unstable in aqueous suspensions, with the initial ζP values in UP below -30 mV and the particle size varying from 148 to 235 nm and 153 to 173 nm for SiNC and SiNC-DCOIT, respectively. In UP, aggregation occurs over time, regardless of the concentration. Additionally, the formation of larger complexes was associated with modifications in the ζP values towards the threshold of stable nanoparticles. In ASW, SiNC and SiNC-DCOIT formed aggregates (<300 nm) independently of the time or concentration, while larger and heterogeneous nanostructures (>300 nm) were detected in the f/2 medium. The pattern of aggregation detected may increase engineering nanomaterial sedimentation rates and enhance the risks towards dwelling organisms.

Engineering a Heterophase Interface by Tailoring the Pt Coverage Density on an Amorphous Ru Surface for Ultrasensitive H2S Detection.

Amorphous/crystalline heterophase engineering is emerging as an attractive strategy to adjust the properties and functions of nanomaterials. Here, we reveal a heterophase interface role by precisely tailoring the crystalline Pt coverage density on an amorphous Ru surface (cPt/aRu) for ultrasensitive H2S detection. We found that when the atomic ratio of Pt/Ru increased from 10 to 50%, the loading modes of Pt changed from island coverage (1cPt/aRu) to cross-linkable coverage (3cPt/aRu) and further to dense coverage (5cPt/aRu). The differences in coverage models further regulate the chemical adsorption of H2S on Pt and the electronic transformation process on Ru, which can be proved by ex situ X-ray photoelectron spectroscopy experiments. Notably, a special cross-linkable coverage 3cPt/aRu on ZnO shows the best gas-sensitive performance, in which the operating temperature reduces from 240 to 160 °C compared with pristine ZnO and the selectivity coefficient for H2S gas improves from ∼1.2 to ∼4.6. This is mainly benefit from the maximized exposure of the amorphous/crystalline heterophase interface. Our work thus provides a new platform for future applications of amorphous/crystalline heterogeneous nanostructures in gas sensors and catalysis.

Synergistic enhancement of high temperature strength and ductility with a novel γ/ε dual-phase hetero-nanostructure in NiCoCr-based alloys

In most γ"-strengthened superalloys, the γ"→δ stabilization is generally considered as an unfavorable transformation process due to the incapability of δ phase on conferring high-temperature strengthening. While recent studies in multi-component alloys indicate that another stabilized γ" phase (ε phase with D019 structure) has been found and proven to be beneficial to mechanical properties. This work shows that the precipitation of ε phase could be tailored in such a way, that it is accompanied by the formation of nano-twins in low stacking fault energy NiCoCr-based multi-component alloys, establishing a unique matrix/(nano-twin/ε/nano-twin)/matrix double-stacked-sandwich heterogeneous nanostructure. This novel ε-plate/nano-twin structure has been found to provide satisfying high temperature strength-ductility synergy and structural stability after aging, thereby leading to a yield-strength enhancement of ∼120% at 25 °C and ∼98% at 700 °C, respectively, while still maintaining sound ductilities. This unique self-organized, heterogeneous, lamellar nanostructure opens up new avenues for further development of hierarchically-nanostructured, high-temperature structural materials.

Stabilization of the Nano-Sized 1T Phase through Rhenium Doping in the Metal-Organic CVD MoS2 Films.

Heterogeneous nanostructures composed of metastable tetragonal 1T-MoS2 and stable hexagonal 2H-MoS2 phases are highly promising for a wide range of applications, including catalysis and ion batteries, due to the high electrical conductivity and catalytic activity of the 1T phase. However, a controllable synthesis of stabilized 1T-MoS2 films over the wafer-scale area is challenging. In this work, a metal-organic chemical vapor deposition process allowing us to obtain ultrathin MoS2 films containing both 1T and 2H phases and control their ratio through rhenium doping was suggested. As a result, Mo1-xRexS2 films with a 1T-MoS2 fraction up to ≈30% were obtained, which were relatively stable under normal conditions for a long time. X-ray photoelectron spectroscopy and Raman spectroscopy also indicated that the 1T-MoS2 phase fraction increased with rhenium concentration increase saturating at Re concentrations above 5 at. %. Also, its concentration was found to significantly affect the film resistivity. Thus, the resistivity of the film containing approximately 30% of the 1T phase was about 130 times lower than that of the film without the 1T phase.

Radical ionic liquid: An efficient self-probe to study heterogeneous structure in glassy state using EPR spectroscopy

Ionic liquids (ILs) exhibit a number of unique properties, including formation of various heterogeneities in their liquid and glassy states. Electron Paramagnetic Resonance (EPR) spectroscopy has proven informative in studies of such heterogeneous nanostructures; however it employs additional small paramagnetic molecules – spin probes – dissolved in ILs as reporters. In this work we synthesized two radical-ILs, which include integrated paramagnetic fragments in their structures, and employed them in continuous wave (CW) and pulse EPR studies of structural peculiarities in IL glasses. In this approach no external-to-IL spin probe is required. We have shown that the trends observed with radical-ILs are similar to those obtained previously using external-to-IL spin probes. In particular, unusual structural anomalies near glass transition temperatures, which were previously found using external-to-IL spin probes, have been now observed using radical-ILs, thus confirming their genuine origin. In general, radical-ILs can be considered as efficient tools to study heterogeneous structure of ILs using EPR.

Enhanced hydrogen generation via overall water splitting using novel MoS2-BN nanoflowers assembled TiO2 ternary heterostructures

Envisaging headway in the applicability of sustainable H2 energy, the novel report of the fabrication of MoS2-BN/TiO2 (MBT) heterogeneous nanostructures has been proposed via facile in-situ hydrothermal route with an aim to propound the superior substitute of noble metal based conventionally employed catalytic system to surmount their exorbitant cost. We inferred the ascendancy of MoS2-BN nanoflowers over pristine MoS2 counterpart in an establishment of TiO2 based heterostructured catalysis. MBT heterostrucutres were extensively scrutinized with respect to their structural, optoelectronic and computational characteristics. En route to enhanced H2 evolution, we have investigated the significance of interfacial junctions and exposed sites in the MBT heterostructures. In order to achieve broader pertinence in green H2 fuel, the performance of MBT heterostrucutres was ascertained with subject to photochemical, electrochemical and photo-electrochemical (PEC) water splitting. Loaded concentration of MoS2-BN was varied in MBT catalysts and 2.5 wt% MoS2-BN/TiO2 exhibited optimum photocatalytic response with an H2 production rate of 2.6 mmol/g/h with 6.94% AQY and improved photo-current response of 0.99 mA/cm2 towards PEC. Electrochemical investigations further intensified the caliber of MBT as HER catalyst ascribed to the higher cathodic current density of 49.23 mA/cm2 at 1.22 V potential. The advancement in the catalytic efficiency of MBT heterostructures was evidenced by the synergetic relationship between MoS2-BN and TiO2 which stimulated the separation and transfer of photo-charged carriers, and lowered the overpotential values consequently surging the kinetics of H2 evolution.

Effect of imperfect interface on the effective properties of elastic micropolar multilaminated nanostructures

AbstractIn this paper, the problem of a heterogeneous elastic micropolar nanostructure with a periodic structure subject to imperfect contact conditions is analyzed through the two‐scale asymptotic homogenization method (AHM). The imperfect interface is modeled as a generalization of the well‐known spring model; that is, the homogeneous imperfect interface is described by the following conditions: tractions and coupled stress are continuous, but displacements and microrotations are discontinuous across the imperfect interface. The jumps in displacements and microrotations are proportional to the interface traction and coupled stress components, respectively. In particular, micropolar multilaminated nanocomposites with centro‐symmetric isotropic constituents and imperfect contact conditions are studied. From AHM, the solutions for the displacement and microrotation fields are found by means of two‐scale series expansions depending on a local (microscopic) variable and a global (macroscopic) variable. The local problem statements and the corresponding effective properties are explicitly described. The formulation depends on the constituent physical properties, the imperfection parameters, the cell length in the y3‐direction, and the phase's volume fractions. Numerical results are illustrated and discussed. We concluded that the effective moduli are affected by the imperfections and the cell length in the y3‐direction.

An ultra-strong and ductile crystalline-amorphous nanostructured surface layer on TiZrHfTaNb0.2 high-entropy alloy by laser surface processing

Heterogeneous crystalline-amorphous nanostructures have been documented to show superior strength-ductility synergy via the co-deformation cooperative effects of nanograins and amorphous grain boundaries. In this work, a facile laser surface remelting technique with rapid cooling rate was successfully developed to fabricate a ∼ 100 μm-thick gradient nanostructured layer accompanied by phase decomposition on a TiZrHfTaNb0.2 high-entropy alloy, where a ∼ 5 μm-thick crystalline-amorphous nanostructured top surface layer with an average grain size of ∼ 7 nm was obtained. Such crystalline-amorphous nanostructured layer shows an ultrahigh yield strength of ∼ 6.0 GPa and a compression strain of ∼ 25 % during the localized micro-pillar compression tests. The atomic observations reveal that co-deformation cooperative mechanisms include the well-retained dislocation activities in nanograins but crystallization in amorphous grain boundaries, which subsequently lead to the grain coarsening via grain boundary-mediated plasticity. This study sheds light on the development of high-performance high-entropy alloys with novel crystalline-amorphous nanostructures and provides significant insight into their plastic deformation mechanisms.

Inverted magnetic response in severe plastically deformed nanostructured high-entropy alloy

We present unconventional magnetization in a high-pressure torsion (HPT) CoCrFeNi nanostructured high-entropy alloy: (i) the temperature dependent magnetization protocol and DC susceptibility suggest effects of spin-clustering. Moreover, HPT-processing of the alloy produces a heterogeneous and metastable nanostructure, changing its supermagnetic character: turning superparamagnetic to superspin glass dynamics, (ii) the material shows an inverted magnetic hysteresis loop, an inversion of the central part of the loop where the remanent magnetization points in a direction opposite to the applied field. The exquisite tunability of this inverted magnetism as a function of field and temperature and its reproducibility in a quasi-equilibrium setting make this spin-clustering phenomenon unique. We account for this phenomenon in terms of a non-equilibrium population of oppositely polarized domains of an ordered ferromagnetic state, enabled through the nanostructured, highly distorted, and locally disordered crystalline medium.

Single microgel degradation governed by heterogeneous nanostructures.

Although the degradation of colloidal particles is one of the most attractive phenomena in the field of biological and environmental science, the degradation mechanism of single particles remains to be elucidated. In this study, in order to clarify the impact of the structure of a single particle on the oxidative degradation processes, thermoresponsive colloidal particles with chemical cleavage points were synthesized as a model, and their degradation behavior was evaluated using high-speed atomic force microscopy (HS-AFM) as well as conventional scattering techniques. The real-time observation of single-particle degradation revealed that the degradation behavior of microgels is governed by their inhomogeneous nanostructure, which originates from the polymerization method and their hydrophilicity. Our findings can be expected to advance the design of carriers for drug-delivery and the understanding of the formation processes of micro (nano)plastics.

Heterogeneous interface-triggered electronic reconfiguration of cobalt-based sulfide electrocatalysts modified by coupling CeO2 for H2 production

It is pivotal but difficult to formulate bifunctional catalysts for electrochemical water splitting that are earth-abundant. Coupling CeO2 can not only improve the sluggish intrinsic OER activity of Co3S4 but also ameliorate the overall catalytic activity. Herein, vertically hierarchical amorphous Co3S4-CeO2 (Co3S4 and CeO2 were used as the main components, so it’s named Co3S4-CeO2) porous nanorods arrays were prepared via relatively facile anion intercalation enhanced electrodeposition on nickel foams (NFs) and following high-temperature vulcanization. Moreover, several characterization techniques, including XRD, were used to demonstrate that the Co3S4-CeO2 heterostructure was successfully synthesized. In both HER and OER, the Co3S4-CeO2 electrode showed remarkable electrochemical performance in alkaline solutions, only 120 mV overpotential and 280 mV drive are needed for the current densities of 10 mA•cm−2 in HER and 50 mA•cm−2 in OER, respectively. The Co3S4-CeO2 electrodes used as the anode and cathode in the double electrode alkaline electrolytic cell enable a value of 1.55 V at 10 mA•cm−2, also the electrolytic cell can sustain for at least 40 h without obvious attenuation. This work offers a straightforward technique for generating heterogeneous nanostructures as well as strong proof that CeO2 can be efficaciously coupled.

Synthesis, characterization, and 5-fluorouracil release behavior of superparamagnetic γ-Fe2O3/ZnO hetero-nanostructures for biomedical applications

In this study, superparamagnetic maghemite (γ-Fe2O3) nanosystems in the form of nanoparticles were fabricated through the co-precipitation method at different processing conditions. Additionally, novel γ-Fe2O3/ZnO heterostructures were fabricated using zinc acetate as the zinc source and polyvinyl pyrrolidone (PVP), and ethylenediaminetetraacetic acid (EDTA) as the capping agents. The results revealed that the size of the crystallites of the prepared maghemite nanopowders was between 6 nm and 7.8 nm depending on the synthesis temperature. The saturation magnetization value of maghemite nanopowders synthesized at 90 °C was measured to be 51.58 emu/g without hysteresis with negligible coercivity. FTIR analysis results proved the presence of ZnO in the maghemite core-based nanosystem. The formation of a ZnO coating using zinc acetate in the presence of PVP and EDTA as a capping agent caused a decrease in magnetization value to 12 emu/g. A ZnO coating provided better dispersion of maghemite nanoparticles and it also affected the drug (5-FU) delivery behavior. ZnO-coated nanoparticles showed prolonged and sustained drug release additionally, they continue to release the drug after 410 h. The 5-FU release kinetics of the prepared heterogeneous nanostructures fitted well with the Korsmeyer-Peppas model.

Rational design of trimetallic AgPt–Fe3O4 nanozyme for catalyst poisoning-mediated CO colorimetric detection

Carbon monoxide (CO) is not only a highly poisonous gas that brings great health risk, but also a significant signaling molecule in body. However, it is still challengeable for development of alternative colorimetric probes to traditional organic chromophores for simple, sensitive and convenient CO sensing. Here, for the first time, we rationally design a novel hydrophilic AgPt–Fe3O4 nanozyme with a unique heterodimeric nanostructure for colorimetric sensing of CO based on the excellent peroxidase-like catalytic activity as well as highly poisonous effect of CO on the nanozyme's catalytic activity. Both experimental evidence and theoretical calculations reveal the trimetallic AgPt–Fe3O4 nanozyme is susceptible to poisoning with the strongest affinity towards CO compared to individual Fe3O4 or Ag–Fe3O4, which is attributed to the adequate exposure of the active metallic sites and efficient interfacial synergy of unique heterodimeric nanostructure. Accordingly, a novel nanozyme-based colorimetric strategy is developed for CO detection with a low detection limit of 5.6 ppb in solution. Furthermore, the probe can be prepared as very convenient test strips and integrated with the portable smartphone platforms for detecting CO gas samples with a low detection limit of 8.9 ppm. Overall, our work proposes guidelines for the rational design of metallic heterogeneous nanostructure to expand the analytical application of nanozyme.

Effect of volume fractions of gradient transition layer on mechanical behaviors of nanotwinned Cu

Heterogeneous nanostructured (HNS) materials, such as gradient and laminated nanostructured metals, possess superior mechanical properties with respect to their homogeneous counterparts. The additional strengthening mechanism of HNS is mainly attributed to the non-uniform plastic deformation induced by gradient transition layers (GTLs) between components. Here, we designed three gradient nanotwinned (GNT) Cu samples with different volume fractions of GTLs (fg) of 10%, 50% and 100% while the rule-of-mixture strength and overall structural gradient are constant to quantitatively reveal its effect on the extra strengthening behaviors. As fg increases, the yield strength is improved and the elastic to plastic stage is prolonged at small strain. Moreover, larger fg suppresses the strain localization and reduces nucleation of cracks at larger strain, accompanied by more widely distributed geometrically necessary dislocations (GNDs) and more bundles of concentrated dislocations (BCDs), thus improving the elongation. Stress partitioning analysis and numerical simulations show that the more widely-distributed GNDs at larger fg result in higher overall back stresses but hardly affect effective stresses, indicative of the origin of the improved strengthening. Such GND-distribution dominated strengthening mechanism paves a fundamental way for developing higher-performance HNS materials.

Reciprocal polariton-induced transparency in alpha-molybdenum trioxide-graphene heteronanostructures

An ultrathin heterogeneous nanostructure consisting of periodic orthorhombic-phase molybdenum trioxide (α-MoO3), graphene nanoribbons, and a dielectric spacer layer has been proposed. Coupling between a hyperbolic phonon polariton from α-MoO3 and a surface plasmon polariton from graphene leads to the presence of reciprocal polariton-induced transparency (RPoIT). The near-field coupling is further evaluated by combining the current distribution values of the multipole decomposition. The RPoIT can be controlled by changing the structural parameters and tuning the chemical potential of graphene. Effects of the incidence angle and polarization angle have been investigated thoroughly from the finite-difference time-domain calculations. The potential applications in the refractive index sensor and mid-infrared (MIR) absorbers have also been investigated. This research provides a clear understanding and practical guidance for the realization of tunable RPoIT, which is desirable from the development of nano-devices and multifunctional hybrid polarization devices in the MIR region.

In situ synthesis of hierarchically-assembled three-dimensional ZnS nanostructures and 3D printed visualization

Nanomaterials have gained enormous interest in improving the performance of energy harvest systems, biomedical devices, and high-strength composites. Many studies were performed fabricating more elaborate and heterogeneous nanostructures then the structures were characterized using TEM tomographic images, upgrading the fabrication technique. Despite the effort, intricate fabrication process, agglomeration characteristic, and non-uniform output were still limited to presenting the 3D panoramic views straightforwardly. Here we suggested in situ synthesis method to prepare complex and hierarchically-assembled nanostructures that consisted of ZnS nanowire core and nanoparticles under Ag2S catalyst. We demonstrated that the vaporized Zn and S were solidified in different shapes of nanostructures with the temperatures solely. To our knowledge, this is the first demonstration of synthesizing heterogeneous nanostructures, consisting of a nanowire from the vapor–liquid–solid and then nanoparticles from the vapor–solid grown mechanism by in situ temperature control. The obtained hierarchically-assembled ZnS nanostructures were characterized by various TEM technologies, verifying the crystal growth mechanism. Lastly, electron tomography and 3D printing enabled the nanoscale structures to visualize with centimeter scales. The 3D printing from randomly fabricated nanomaterials is rarely performed to date. The collaborating work could offer a better opportunity to fabricate advanced and sophisticated nanostructures.