Multicomponent Heterostructures Research Articles

Bimetal-organic Framework-derived Co9 S8 /ZnS@NC Heterostructures for Superior Lithium-ion Storage.

Heterostructure engineering of electrode materials, which is expected to accelerate the ion/electron transport rates driven by a built-in internal electric field at the heterointerface, offers unprecedented promise in improving their cycling stability and rate performance. Herein, carbon nanotubes with Co9 S8 /ZnS heterostructures embedded in a N-doped carbon framework (Co9 S8 /ZnS@NC) have been rationally designed via an in-situ vapor chemical transformation strategy with the aid of thiophene, which not only acted as carbon source for the growth of carbon nanotubes but also as sulfur source for the sulfurization of metal Zn and Co. Density functional theory (DFT) calculation shows an about 3.24 eV electrostatic potential difference between ZnS and Co9 S8 , which results in a strong electrostatic field across the interface that makes electrons transfer from Co9 S8 to the ZnS side. As expected, a stable cycling performance with reversible capacity of 411.2 mAh g-1 at 1000 mA g-1 after 300 cycles, excellent rate capability (324 mAh g-1 at 2000 A g-1 ) and a high percentage of pseudocapacitance contribution (87.5% at 2.2 mv/s) for lithium-ion batteries (LIBs) are achieved. This work provides a possible strategy for designing multicomponent heterostructural materials for application in energy storage and conversion fields.

Carbon-Decorated Fe3S4-Fe7Se8 Hetero-Nanowires: Interfacial Engineering for Bifunctional Electrocatalysis Toward Hydrogen and Oxygen Evolution Reactions

The design and synthesis of complex multi-component heterostructures is an effective strategy to fabricate cost-efficient catalysts for electrochemical water splitting. Herein, one-dimensional porous Fe3S4-Fe7Se8 heterostructured nanowires confined in carbon (Fe3S4-Fe7Se8@C) were synthesized via the selenization of Fe-based organic-inorganic nanowires. Benefiting from the merits of morphology, composition and surface structure characteristics, i.e., the high structural void porosity, the direct electrical pathways of nanowire topology and the conductive carbon layer coating, the titled catalyst not only offered a larger accessible electrocatalytic interface but also facilitated diffusion of the electrolyte and gas. Moreover, the electron redistribution at the Fe3S4-Fe7Se8 heterojunction interfaces reduced the adsorption free-energy barriers on the active sites, endowing the catalysts with faster reaction kinetics and improved electrocatalytic activity. Accordingly, the optimal Fe3S4-Fe7Se8@C produced a low hydrogen evolution reaction overpotential of 124 mV at 10 mA cm−2 with a Tafel slope of 111.2 mV dec−1, and an ultralow oxygen evolution reactions overpotential of 219 mV at 20 mA cm−2, respectively. When applied as both anode and cathode for overall water splitting, a low battery voltage of 1.67 V was achieved along with excellent stability for at least 12 h. The work presented here offered a feasible scheme to fabricate non-noble metal-based electrocatalysts for water splitting.

Advanced water splitting electrocatalysts via the design of multicomponent heterostructures.

The design of multicomponent heterostructures for electrocatalysts is a promising strategy for enhancing electrocatalytic activities. This significant achievement, which is made possible by multicomponent heterostructure engineering, mainly arises from the ability to balance the adsorption and desorption of intermediates. Herein, the design of multicomponent heterostructures is highlighted by presenting recent achievements in electrocatalysis, focusing on the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Finally, challenges and perspectives relating to multicomponent heterostructure engineering are presented.

Stability and Exchange Processes in Ionic Liquid/Porphyrin Composite Films on Metal Surfaces.

In light of increasing interest in the development of organic–organic multicomponent heterostructures on metals, this molecular-scale study investigates prototypical composite systems of ultrathin porphyrin and ionic liquid (IL) films on metallic supports under well-defined ultrahigh vacuum conditions. By means of angle-resolved X-ray photoelectron spectroscopy, we investigated the adsorption, stability, and thermal exchange of the resulting films after sequential physical vapor deposition of the free-base porphyrin 5,10,15,20-tetraphenylporphyrin, 2H-TPP, and the IL 1-methyl-3-octylimidazolium hexafluorophosphate, [C8C1Im][PF6], on Ag(111) and Au(111). 2H-TPP shows two-dimensional growth of up to two closed molecular layers on Ag(111) and Au(111) and three-dimensional island growth for thicker films. IL films on top of a monolayer of 2H-TPP exhibit Stranski–Krastanov-like growth and are stable up to 385 K. The 2H-TPP layer leads to destabilization of the IL films, compared to the IL in direct contact with the bare metals, by inhibiting the specific adsorption of the ions on the metal surfaces. When the porphyrin is deposited on top of [C8C1Im][PF6] at low temperature, the 2H-TPP molecules adsorb on top of the IL film at first but replace the IL at the IL/metal interfaces upon heating above 240 K. This exchange process is most likely driven by the higher adsorption energy of 2H-TPP on Ag(111) and Au(111) surfaces, as compared to the IL. The behavior observed on Ag(111) and Au(111) is identical. The results are highly relevant for the stability of porphyrin/IL-based thin film catalyst systems and molecular devices, and more generally, stacked organic multilayer architectures.

Visible-light-activated N-doped CQDs/g-C3N4/Bi2WO6 nanocomposites with different component arrangements for the promoted degradation of hazardous vapors

To investigate whether the arrangement of componentsin multi-composite photocatalysts may affect their photocatalytic properties, due to different charge-transfer routes, two ternary-nanocomposite photocatalysts with different component arrangements, comprising N-doped carbon quantum dots (NCQDs), g-C3N4 (CN), and Bi2WO6 (BWO) (hereafter referred to as NCQDs/CN/BWO), were developed, and the photocatalytic degradation of model hazardous vapors under visible-light illumination was investigated. Type I NCQDs/CN/BWO, which was developed by the combination of NCQDs/BWO and CN, exhibited photocatalytic ability superior to that of type II NCQDs/CN/BWO, which was developed by the combination of CN/BWO and NCQDs; the superior photocatalytic ability corresponded to the dual properties of NCQDs: charge mediation and upconversion photoluminescence. Moreover, the photocatalytic ability of NCQDs/CN/BWO was greater than those of the reference catalysts; in addition, this photocatalyst exhibited outstanding photochemical stability. Additionally, the effects of CN/(BWO + CN) weight ratio of the CN/BWO dual nanocomposites and the NCQDs/(BWO + CN + NCQDs) weight percentage of NCQDs/CN/BWO ternary nanocomposites on the pollutant removal efficiency were investigated. The plausible mechanisms over the two NCQDs/CN/BWO photocatalysts for the degradation of hazardous vapors were discussed. The component arrangement approach proposed herein afforded a technique toward the perceptive development of novel multi-component heterostructures for the photocatalytic degradation of hazardous vapors.

Interface engineering of Ni5P2 nanoparticles and a mesoporous PtRu film heterostructure on Ni foam for enhanced hydrogen evolution

Engineering of multicomponent heterostructures can yield exceptional functionalities and enhance electrocatalytic activities by a synergistic effect. Herein, Ni5P2 nanoparticle-decorated mesoporous PtRu film on Ni foam (Ni5P2-mPtRu/NF) has been synthesized via a facile two-step strategy. Ni5P2-mPtRu/NF possesses a well-developed continuous mesoporous structure and strong electronic interaction between Ni5P2 and PtRu, exhibiting an enhanced electrocatalytic performance towards an alkaline hydrogen evolution reaction (HER). Ni5P2-mPtRu/NF achieves a current density of 10 mA cm−2 at an overpotential of 28.8 mV and a low Tafel slope of 56.5 mV dec−1, and has excellent durability. This work provides a promising pathway for developing self-supported mesoporous multicomponent heterostructures as efficient electrocatalysts for an alkaline HER.

Block-Co-polymer-Assisted Synthesis of All Inorganic Highly Porous Heterostructures with Highly Accessible Thermally Stable Functional Centers.

Here, we propose a simple approach for the design of highly porous multicomponent heterostructures by infiltration of block-co-polymer templates with inorganic precursors in swelling solvents followed by gas-phase sequential infiltration synthesis and thermal annealing. This approach can prepare conformal coatings, free-standing membranes, and powders consisting of uniformly sized metal or metal oxide nanoparticles (NPs) well dispersed in a porous oxide matrix. We employed this new, versatile synthetic concept to synthesize catalytically active heterostructures of uniformly dispersed ∼4.3 nm PdO nanoparticles accessible through three-dimensional pore networks of the alumina support. Importantly, such materials reveal high resistance against sintering at 800 °C, even at relatively high loadings of NPs (∼10 wt %). At the same time, such heterostructures enable high mass transport due to highly interconnected nature of the pores. The surface of synthesized nanoparticles in the porous matrix is highly accessible, which enables their good catalytic performance in methane and carbon monoxide oxidation. In addition, we demonstrate that this approach can be utilized to synthesize heterostructures consisting of different types of NPs on a highly porous support. Our results show that swelling-based infiltration provides a promising route toward the robust and scalable synthesis of multicomponent structures.

Hydrothermal synthesis of ZnSnO3 nanoparticles decorated on g-C3N4 nanosheets for accelerated photocatalytic degradation of tetracycline under the visible-light irradiation

The construction of heterojunction photocatalysts is a significant tactic to facilitate efficient long-lasting photo-generated carriers’ separation, thus improving the photocatalytic performance of the single photocatalysts. In this paper, a multicomponent heterostructure photocatalyst was designed and prepared via a simply hydrothermal method, which was composed of the ZnSnO3 nanoparticles uniformly anchoring on the surface of g-C3N4 nanosheets. The structure and properties of ZnSnO3/g-C3N4 heterojunction photocatalysts were characterized utilizing series of characteristic techniques. Results displayed that introducing 2D g-C3N4 nanosheets not only acted as the support to disperse the ZnSnO3 nanoparticles to confine the aggregation of ZnSnO3 nanoparticles, but also improved the light absorption and the separation of the photogenerated carriers of ZnSnO3, which can positively increase the photocatalytic performance for the tetracycline (TC) degradation under visible light irradiation. And the highest photocatalytic activity was obtained by 10% ZnSnO3/g-C3N4 photocatalyst (85%, 120 min), which was up to nearly 9 times higher than g-C3N4. Accordingly, the corresponding photocatalytic reaction mechanism involving in the separation of the efficient charge carrier was investigated.

A rational design of hollow nanocages Ag@CuO-TiO2 for enhanced acetone sensing performance

Hollow nanostructured Ag@CuO-TiO2 was prepared by a facile hydrothermal method with high surface area and uniform catalyst functionalization. The obtaining of Ag@CuO-TiO2 multicomponent hollow nanocages was ascribed to the addition of TiF4, which serves as both the precursor of TiO2 and etching agent by releasing HF. In this process, Cu2O works as the self-template and the scaffold to induce and maintain the shape of hollow nanocages. Therefore, the formation of hollow structure and multicomponent heterostructures were accomplished without tedious processes and additional template. The deposition of TiO2 layer, anchored to the Ag@Cu2O surface, avoids the aggregation of p-type or n-type nanoparticles and ultimately formation of p–p junctions or n–n junctions, which would be valuable in terms of reproducibility and scalable production. The numerous heterojunctions of CuO-TiO2, well-dispersed nanoscale Ag catalysts and hollow nanocage structures are favorable for the development of high-performance gas sensors. The desired Ag@CuO-TiO2 hollow nanocages were investigated for response to various target gases, which showed a superior sensing performance towards acetone. The improved sensing properties might be ascribed to the synergistic effects of both hollow structure and different nanocomponents.

Constructing a novel Zn2SnO4/C/AgBr nanocomposite with extended spectral response and improved photocatalytic performance

High-efficient photocatalyst based on Zn2SnO4/C/AgBr multi-component heterostructure was prepared via a two-step hydrothermal synthesis method followed by chemical deposition process. Morphological studies showed that ultra-fine AgBr nanoparticles with the size of 3–5 nm were in situ grown on the surface of the carbon layers attached to Zn2SnO4 nanocrystals. UV–vis characterization demonstrated that the co-modification of carbon and AgBr contributed to the dramatically improved light absorption ability of Zn2SnO4/C/AgBr nanocomposites. In the multi-component heterostructured photocatalyst, carbon functioning as a charge mediator plays a pivotal role in separating photogenerated electron-hole pairs efficiently. Zn2SnO4/C/AgBr photocatalysts exhibited a significant enhancement of visible-light photocatalytic performance toward the photodegradation of rhodamine B (RhB), resulting from the synergistic effect of the intensified visible-light absorption capacity and efficient photogenerated electron-hole pairs transfer. In addition, a proposed schematic mechanism for the significant enhancement of photocatalytic performance is as well put forward on the basis of the experimental results.

Voltage-Controlled ON-OFF Ferromagnetism at Room Temperature in a Single Metal Oxide Film.

Electric-field-controlled magnetism can boost energy efficiency in widespread applications. However, technologically, this effect is facing important challenges: mechanical failure in strain-mediated piezoelectric/magnetostrictive devices, dearth of room-temperature multiferroics, or stringent thickness limitations in electrically charged metallic films. Voltage-driven ionic motion (magneto-ionics) circumvents most of these drawbacks while exhibiting interesting magnetoelectric phenomena. Nevertheless, magneto-ionics typically requires heat treatments and multicomponent heterostructures. Here we report on the electrolyte-gated and defect-mediated O and Co transport in a Co3O4 single layer which allows for room-temperature voltage-controlled ON-OFF ferromagnetism (magnetic switch) via internal reduction/oxidation processes. Negative voltages partially reduce Co3O4 to Co (ferromagnetism: ON), resulting in graded films including Co- and O-rich areas. Positive bias oxidizes Co back to Co3O4 (paramagnetism: OFF). This electric-field-induced atomic-scale reconfiguration process is compositionally, structurally, and magnetically reversible and self-sustained, since no oxygen source other than the Co3O4 itself is required. This process could lead to electric-field-controlled device concepts for spintronics.

Three-dimensional directed assembly of organic charge-transfer heterostructure.

Multicomponent crystalline heterostructures are a powerful approach to integrate different functional materials into the ordered structures. Here we describe three-dimensional spherical assembly of binary organic solids that consist of electron donor and acceptor molecules. A mechanistic study of heterostructure formation reveals that the dewetting and drying-mediated assembly processes are responsible for the spherical crystallite formation. The assembled spherical heterostructures are highly tunable, crystalline and chemically stable, exhibiting phase separation controlled optoelectronic behavior. This simple, generalizable three-dimensional assembly can be modified for the formation of ordered functional organic multicomponent heterostructures for emerging applications.

Study of Properties of Multicomponent Heterostructures Based on A<sup>III</sup>B<sup>V</sup> Compounds

Complex analysis of the quality of the surface of the multicomponent epitaxial layers AIIIBV compounds grown at the different conditions of temperature gradient zone recrystallization was performed. Main parameters that determine the quality of the surface and structural perfection of multicomponent heterostructures AlInGaPAs / GaAs have been found: the temperature gradient, the composition of the solution-melt, subcooling, matching the lattice parameters and the CTE of the layer and the substrate, the substrate orientation.

Precise tuning in platinum-nickel/nickel sulfide interface nanowires for synergistic hydrogen evolution catalysis

Comprising abundant interfaces, multicomponent heterostructures can integrate distinct building blocks into single entities and yield exceptional functionalities enabled by the synergistic components. Here we report an efficient approach to construct one-dimensional metal/sulfide heterostructures by directly sulfuring highly composition-segregated platinum-nickel nanowires. The heterostructures possess a high density of interfaces between platinum-nickel and nickel sulfide components, which cooperate synergistically towards alkaline hydrogen evolution reaction. The platinum-nickel/nickel sulfide heterostructures can deliver a current density of 37.2 mA cm−2 at an overpotential of 70 mV, which is 9.7 times higher than that of commercial Pt/C. The heterostructures also offer enhanced stability revealed by long-term chronopotentiometry measurements. The present work highlights a potentially powerful interface-engineering strategy for designing multicomponent heterostructures with advanced performance in hydrogen evolution reaction and beyond.

Charge Transfer Dynamics in CdS and CdSe@CdS Based Hybrid Nanorods Tipped with Both PbS and Pt

The synthesis of hybrid nanostructures that have specific properties has become a significant topic for construction of “smart” nanomaterials for various applications. Formation of hybrid nanostructures, particularly those combining metals and semiconductors, often introduces new chemical, optical, and electronic properties. Here, we show a simple solution phase synthesis of multicomponent heterostructures based on the growth of metal and semiconductor onto the tips of semiconductor nanorods, leading to the formation of a hybrid semiconductor/semiconductor/metal structure. The synthesis involves the reduction of Pt–acetylacetonate to achieve selective growth of a Pt metal tip onto one side of the CdS rod, followed by the thermal decomposition of Pb–bis(diethyldithiocarbamate) to grow a PbS nanocrystal onto the other tip of the nanorod. The band alignment between the two semiconductor components as well as the alignment with the Fermi level of the metal could support intraparticle charge transfer, which is often sought after for photocatalysis applications. Yet, we show, using femtosecond transient differential absorption spectroscopy (TDA), that carrier dynamics in such a hybrid system can be more complex than that predicted simply by bulk band alignment considerations. This highlights the importance of the design of band alignment and interface passivation and its role in affecting carrier dynamics within hybrid nanostructures.

Design and construction of the sandwich-like Z-scheme multicomponent CdS/Ag/Bi2MoO6 heterostructure with enhanced photocatalytic performance in RhB photodegradation

A rationally designed and successfully fabricated all-solid-state Z-scheme photocatalyst, CdS/Ag/Bi2MoO6, with a sandwich-like multicomponent heterostructure, shows an enhanced photocatalytic performance in RhB degradation.

Growth and morphological analysis of segmented AuAg alloy nanowires created by pulsed electrodeposition in ion-track etched membranes.

Background: Multicomponent heterostructure nanowires and nanogaps are of great interest for applications in sensorics. Pulsed electrodeposition in ion-track etched polymer templates is a suitable method to synthesise segmented nanowires with segments consisting of two different types of materials. For a well-controlled synthesis process, detailed analysis of the deposition parameters and the size-distribution of the segmented wires is crucial.Results: The fabrication of electrodeposited AuAg alloy nanowires and segmented Au-rich/Ag-rich/Au-rich nanowires with controlled composition and segment length in ion-track etched polymer templates was developed. Detailed analysis by cyclic voltammetry in ion-track membranes, energy-dispersive X-ray spectroscopy and scanning electron microscopy was performed to determine the dependency between the chosen potential and the segment composition. Additionally, we have dissolved the middle Ag-rich segments in order to create small nanogaps with controlled gap sizes. Annealing of the created structures allows us to influence their morphology.Conclusion: AuAg alloy nanowires, segmented wires and nanogaps with controlled composition and size can be synthesised by electrodeposition in membranes, and are ideal model systems for investigation of surface plasmons.

Ultrafast Exciton Dynamics and Light-Driven H2 Evolution in Colloidal Semiconductor Nanorods and Pt-Tipped Nanorods

Colloidal quantum confined one-dimensional (1D) semiconductor nanorods (NRs) and related semiconductor-metal heterostructures are promising new materials for efficient solar-to-fuel conversion because of their unique physical and chemical properties. NRs can simultaneously exhibit quantum confinement effects in the radial direction and bulk like carrier transport in the axial direction. The former implies that concepts well-established in zero-dimensional quantum dots, such as size-tunable energetics and wave function engineering through band alignment in heterostructures, can also be applied to NRs; while the latter endows NRs with fast carrier transport to achieve long distance charge separation. Selective growth of catalytic metallic nanoparticles, such as Pt, at the tips of NRs provides convenient routes to multicomponent heterostructures with photocatalytic capabilities and controllable charge separation distances. The design and optimization of such materials for efficient solar-to-fuel conversion require the understanding of exciton and charge carrier dynamics. In this Account, we summarize our recent studies of ultrafast charge separation and recombination kinetics and their effects on steady-state photocatalytic efficiencies of colloidal CdS and CdSe/CdS NRs and related NR-Pt heterostructures. After a brief introduction of their electronic structure, we discuss exciton dynamics of CdS NRs. By transient absorption and time-resolved photoluminescence decay, it is shown that although the conduction band electrons are long-lived, photogenerated holes in CdS NRs are trapped on an ultrafast time scale (∼0.7 ps), which forms localized excitons due to strong Coulomb interaction in 1D NRs. In quasi-type II CdSe/CdS dot-in-rod NRs, a large valence band offset drives the ultrafast localization of holes to the CdSe core, and the competition between this process and ultrafast hole trapping on a CdS rod leads to three types of exciton species with distinct spatial distributions. The effect of the exciton dynamics on photoreduction reactions is illustrated using methyl viologen (MV(2+)) as a model electron acceptor. The steady-state MV(2+) photoreduction quantum yield of CdSe/CdS dot-in-rod NRs approaches unity under rod excitation, much larger than CdSe QDs and CdSe/CdS core/shell QDs. Detailed time-resolved studies show that in quasi-type II CdSe/CdS NRs and type II ZnSe/CdS NRs strong quantum confinement in the radial direction facilitates fast electron transfer and hole removal, whereas the fast carrier mobility along the axial direction enables long distance charge separation and slow charge recombination, which is essential for efficient MV(2+) photoreduction. The NR/MV(2+) relay system can be coupled to Pt nanoparticles in solution for light-driven H2 generation. Alternatively, Pt-tipped CdS and CdSe/CdS NRs provide fully integrated all inorganic systems for light-driven H2 generation. In CdS-Pt and CdSe/CdS-Pt hetero-NRs, ultrafast hole trapping on the CdS rod surface or in CdSe core enables efficient electron transfer from NRs to Pt tips by suppressing hole and energy transfer. It is shown that the quantum yields of photodriven H2 generation using these heterostructures correlate well with measured hole transfer rates from NRs to sacrificial donors, revealing that hole removal is the key efficiency-limiting step. These findings provide important insights for designing more efficient quantum confined NR and NR-Pt based systems for solar-to-fuel conversion.

Investigation of heterostructure influence upon characteristics based on simulation

Basic performance characteristics of multicomponent nanoscale heterostructures are investigated. Graphs are presented of such computer-simulated performance indicators as current-voltage characteristics and the dependence of internal quantum efficiency on the doping of barriers in a quantum-size region.

Influence of growth conditions on the surface quality and structural perfection of multicomponent heterostructures based on group A3B5 compounds

The surface quality of epitaxial multicomponent layers based on group A3B5 compounds, which are grown under different conditions via floating-zone refining with a temperature gradient, is comprehensively analyzed. The main parameters (temperature gradient, solution-melt composition, supercooling level, matching between lattice parameters and the thermal expansion coefficients of the layer and substrate, and substrate orientation) affecting the surface quality and structural perfection of the heterostructures are determined.