Showing papers by "Hua Zhang published in 2018"
TL;DR: This review summarizes the recent advances in the synthesis of 2D MOF nanosheets by using top-down methods, e.g. sonication exfoliation, mechanical ex foliation, Li-intercalation exfoliated and chemical exfolation, and bottom-up methods, i.e. interfacial synthesis, three-layer synthesis, surfactant-assisted synthesis, modulated synthesis, and sonication synthesis.
Abstract: Two-dimensional (2D) metal–organic framework (MOF) nanosheets are attracting increasing research attention due to their unique properties originating from their ultrathin thickness, large surface area and high surface-to-volume atom ratios. Many great advances have been made in the synthesis and application of 2D MOF nanosheets over the past few years. In this review, we summarize the recent advances in the synthesis of 2D MOF nanosheets by using top-down methods, e.g. sonication exfoliation, mechanical exfoliation, Li-intercalation exfoliation and chemical exfoliation, and bottom-up methods, i.e. interfacial synthesis, three-layer synthesis, surfactant-assisted synthesis, modulated synthesis, and sonication synthesis. In addition, the recent progress in 2D MOF nanosheet-based nanocomposites is also briefly introduced. The potential applications of 2D MOF nanosheets in gas separation, energy conversion and storage, catalysis, sensors and biomedicine are discussed. Finally, we give our personal insights into the challenges and opportunities for the future research of 2D MOF nanosheets and their composites.
842 citations
TL;DR: It is shown that micrometre-sized metallic 1T′-MoS2- and 1T-MoSe2-layered crystals can be prepared in high phase purity on a large scale, and that they display promising electrocatalytic activity towards the hydrogen evolution reaction.
Abstract: Phase control plays an important role in the precise synthesis of inorganic materials, as the phase structure has a profound influence on properties such as conductivity and chemical stability. Phase-controlled preparation has been challenging for the metallic-phase group-VI transition metal dichalcogenides (the transition metals are Mo and W, and the chalcogens are S, Se and Te), which show better performance in electrocatalysis than their semiconducting counterparts. Here, we report the large-scale preparation of micrometre-sized metallic-phase 1T′-MoX2 (X = S, Se)-layered bulk crystals in high purity. We reveal that 1T′-MoS2 crystals feature a distorted octahedral coordination structure and are convertible to 2H-MoS2 following thermal annealing or laser irradiation. Electrochemical measurements show that the basal plane of 1T′-MoS2 is much more active than that of 2H-MoS2 for the electrocatalytic hydrogen evolution reaction in an acidic medium.
657 citations
TL;DR: The general synthetic strategies applied to 2D metal nanomaterials are briefly introduced, followed by describing in detail the various synthetic methods classified in two categories, i.e. bottom-up methods and top-down methods.
Abstract: As one unique group of two-dimensional (2D) nanomaterials, 2D metal nanomaterials have drawn increasing attention owing to their intriguing physiochemical properties and broad range of promising applications. In this Review, we briefly introduce the general synthetic strategies applied to 2D metal nanomaterials, followed by describing in detail the various synthetic methods classified in two categories, i.e. bottom-up methods and top-down methods. After introducing the unique physical and chemical properties of 2D metal nanomaterials, the potential applications of 2D metal nanomaterials in catalysis, surface enhanced Raman scattering, sensing, bioimaging, solar cells, and photothermal therapy are discussed in detail. Finally, the challenges and opportunities in this promising research area are proposed.
625 citations
TL;DR: The first paradigm of a high-rate and ultrastable flexible quasi-solid-state zinc-ion battery is constructed from a novel 2D ultrathin layered zinc orthovanadate array cathode, a Zn array anode supported by a conductive porous graphene foam, and a gel electrolyte.
Abstract: Zinc-ion batteries are under current research focus because of their uniqueness in low cost and high safety. However, it is still desirable to improve the rate performance by improving the Zn2+ (de)intercalation kinetics and long-cycle stability by eliminating the dendrite formation problem. Herein, the first paradigm of a high-rate and ultrastable flexible quasi-solid-state zinc-ion battery is constructed from a novel 2D ultrathin layered zinc orthovanadate array cathode, a Zn array anode supported by a conductive porous graphene foam, and a gel electrolyte. The nanoarray structure for both electrodes assures the high rate capability and alleviates the dendrite growth. The flexible Zn-ion battery has a depth of discharge of ≈100% for the cathode and 66% for the anode, and delivers an impressive high-rate of 50 C (discharge in 60 s), long-term durability of 2000 cycles at 20 C, and unprecedented energy density ≈115 Wh kg-1 , together with a peak power density ≈5.1 kW kg-1 (calculation includes masses of cathode, anode, and current collectors). First principles calculations and quantitative kinetics analysis show that the high-rate and stable properties are correlated with the 2D fast ion-migration pathways and the introduced intercalation pseudocapacitance.
534 citations
TL;DR: A new approach of developing atomic epitaxial in-growth in Co-Ni3 N nanowires array is devised, where a nanoconfinement effect is reinforced at the interface, leading to a significant enhancement in catalytic activities for both hydrogen and oxygen evolution reactions.
Abstract: Electrocatalytic performance can be enhanced by engineering a purposely designed nanoheterojunction and fine-tuning the interface electronic structure. Herein a new approach of developing atomic epitaxial in-growth in Co-Ni3 N nanowires array is devised, where a nanoconfinement effect is reinforced at the interface. The Co-Ni3 N heterostructure array is formed by thermal annealing NiCo2 O4 precursor nanowires under an optimized condition, during which the nanowire morphology is retained. The epitaxial in-growth structure of Co-Ni3 N at nanometer scale facilitates the electron transfer between the two different domains at the epitaxial interface, leading to a significant enhancement in catalytic activities for both hydrogen and oxygen evolution reactions (10 and 16 times higher in the respective turn-over frequency compared to Ni3 N-alone nanorods). The interface transfer effect is verified by electronic binding energy shift and density functional theory (DFT) calculations. This nanoconfinement effect occurring during in situ atomic epitaxial in-growth of the two compatible materials shows an effective pathway toward high-performance electrocatalysis and energy storages.
373 citations
TL;DR: This Review summarizes the commonly used routes to build 3D TMD architectures and highlights their applications in electrochemical energy storage and conversion, including batteries, supercapacitors, and electrocatalytic hydrogen evolution.
Abstract: Transition metal dichalcogenides (TMDs) have attracted considerable attention in recent years due to their unique properties and promising applications in electrochemical energy storage and conversion. However, the limited number of active sites and blocked ion and mass transport severely impair the electrochemical performance of TMDs. Construction of three-dimensional (3D) architectures from TMD nanomaterials has been proven an effective strategy to solve the aforementioned problems due to their large specific surface area and short ion and mass transport distance. Here, we summarize the commonly used routes to build 3D TMD architectures and highlight their applications in electrochemical energy storage and conversion, including batteries, supercapacitors, and electrocatalytic hydrogen evolution. Moreover, the challenges and outlooks in this research area are also discussed.
363 citations
TL;DR: This work provides a universal and effective way toward the synthesis of TMD nanostructures with abundant active sites for electrocatalysis, which can also be used for other applications such as batteries, sensors, and bioimaging.
Abstract: Nanostructured transition metal dichalcogenides (TMDs) are proven to be efficient and robust earth-abundant electrocatalysts to potentially replace precious platinum-based catalysts for the hydrogen evolution reaction (HER). However, the catalytic efficiency of reported TMD catalysts is still limited by their low-density active sites, low conductivity, and/or uncleaned surface. Herein, a general and facile method is reported for high-yield, large-scale production of water-dispersed, ultrasmall-sized, high-percentage 1T-phase, single-layer TMD nanodots with high-density active edge sites and clean surface, including MoS2 , WS2 , MoSe2 , Mo0.5 W0.5 S2 , and MoSSe, which exhibit much enhanced electrochemical HER performances as compared to their corresponding nanosheets. Impressively, the obtained MoSSe nanodots achieve a low overpotential of -140 mV at current density of 10 mA cm-2 , a Tafel slope of 40 mV dec-1 , and excellent long-term durability. The experimental and theoretical results suggest that the excellent catalytic activity of MoSSe nanodots is attributed to the high-density active edge sites, high-percentage metallic 1T phase, alloying effect and basal-plane Se-vacancy. This work provides a universal and effective way toward the synthesis of TMD nanostructures with abundant active sites for electrocatalysis, which can also be used for other applications such as batteries, sensors, and bioimaging.
310 citations
TL;DR: A systematic study of spinel ZnFex Co2-x O4 oxides toward the OER is presented and a highly active catalyst superior to benchmark IrO2 is developed and the distinctive OER activity is found to be dominated by the metal-oxygen covalency and an enlarged CoO covalencies by 10-30 at% Fe substitution is responsible for the activity enhancement.
Abstract: Cobalt-containing spinel oxides are promising electrocatalysts for the oxygen evolution reaction (OER) owing to their remarkable activity and durability. However, the activity still needs further improvement and related fundamentals remain untouched. The fact that spinel oxides tend to form cation deficiencies can differentiate their electrocatalysis from other oxide materials, for example, the most studied oxygen-deficient perovskites. Here, a systematic study of spinel ZnFex Co2-x O4 oxides (x = 0-2.0) toward the OER is presented and a highly active catalyst superior to benchmark IrO2 is developed. The distinctive OER activity is found to be dominated by the metal-oxygen covalency and an enlarged CoO covalency by 10-30 at% Fe substitution is responsible for the activity enhancement. While the pH-dependent OER activity of ZnFe0.4 Co1.6 O4 (the optimal one) indicates decoupled proton-electron transfers during the OER, the involvement of lattice oxygen is not considered as a favorable route because of the downshifted O p-band center relative to Fermi level governed by the spinel's cation deficient nature.
306 citations
TL;DR: This review highlights the quantified performances of reported wearable electrochemical energy storage devices, as well as their micro-sized counterparts under specific mechanical deformations, which can be used as the benchmark for future studies in this field.
Abstract: Compatible energy storage devices that are able to withstand various mechanical deformations, while delivering their intended functions, are required in wearable technologies. This imposes constraints on the structural designs, materials selection, and miniaturization of the cells. To date, extensive efforts have been dedicated towards developing electrochemical energy storage devices for wearables, with a focus on incorporation of shape-conformable materials into mechanically robust designs that can be worn on the human body. In this review, we highlight the quantified performances of reported wearable electrochemical energy storage devices, as well as their micro-sized counterparts under specific mechanical deformations, which can be used as the benchmark for future studies in this field. A general introduction to the wearable technology, the development of the selection and synthesis of active materials, cell design approaches and device fabrications are discussed. It is followed by challenges and outlook toward the practical use of electrochemical energy storage devices for wearable applications.
292 citations
TL;DR: In this paper, the authors proposed a conductive hydrogel with intrinsic flexibility, high sensitivity, linearity, and outstanding reliability for wearable devices or implantable sensors, which can be used for wearable sensors.
Abstract: Biocompatible conductive hydrogels with intrinsic flexibility, high sensitivity, linearity and outstanding reliability are highly demanded for wearable devices or implantable sensors. Here we repor...
286 citations
TL;DR: A simple solvothermal method to synthesize a series of MoS2 nanosheets@nitrogen-doped graphene composites is developed, demonstrating the significance in surface-controlled pseudocapacitance contribution at the high rate and offering some meaningful preparation and investigation experiences for designing electrode materials for commercial sodium-ion batteries with favorable performance.
Abstract: Transition-metal disulfide with its layered structure is regarded as a kind of promising host material for sodium insertion, and intensely investigated for sodium-ion batteries. In this work, a simple solvothermal method to synthesize a series of MoS2 nanosheets@nitrogen-doped graphene composites is developed. This newly designed recipe of raw materials and solvents leads the success of tuning size, number of layers, and interplanar spacing of the as-prepared MoS2 nanosheets. Under cut-off voltage and based on an intercalation mechanism, the ultrasmall MoS2 nanosheets@nitrogen-doped graphene composite exhibits more preferable cycling and rate performance compared to few-/dozens-layered MoS2 nanosheets@nitrogen-doped graphene, as well as many other reported insertion-type anode materials. Last, detailed kinetics analysis and density functional theory calculation are also employed to explain the Na+ - storage behavior, thus proving the significance in surface-controlled pseudocapacitance contribution at the high rate. Furthermore, this work offers some meaningful preparation and investigation experiences for designing electrode materials for commercial sodium-ion batteries with favorable performance.
TL;DR: A review of the state of the art in the field of epitaxial growth of hybrid nanostructures can be found in this article, where the authors discuss the historical development, architectures and compositions, epitaxy methods, characterization techniques, and advantages of hybrid nano-structures.
Abstract: Hybrid nanostructures are a class of materials that are typically composed of two or more different components, in which each component has at least one dimension on the nanoscale. The rational design and controlled synthesis of hybrid nanostructures are of great importance in enabling the fine tuning of their properties and functions. Epitaxial growth is a promising approach to the controlled synthesis of hybrid nanostructures with desired structures, crystal phases, exposed facets and/or interfaces. This Review provides a critical summary of the state of the art in the field of epitaxial growth of hybrid nanostructures. We discuss the historical development, architectures and compositions, epitaxy methods, characterization techniques and advantages of epitaxial hybrid nanostructures. Finally, we provide insight into future research directions in this area, which include the epitaxial growth of hybrid nanostructures from a wider range of materials, the study of the underlying mechanism and determining the role of epitaxial growth in influencing the properties and application performance of hybrid nanostructures. Epitaxial hybrid nanostructures can show different functionalities and superior performance in applications from those of the individual components. This Review discusses the methods of preparation and techniques for characterization of epitaxial hybrid nanostructures with various architectures, and examines the role of epitaxial growth in influencing the properties and application performance of hybrid nanostructures.
TL;DR: The synthesis of a new type of MOF@COF core-shell hybrid material, i.e., NH2 -MIL-68@TPA-COF, with high crystallinity and hierarchical pore structure, is synthesized and used as an effective visible-light-driven photocatalyst for the degradation of rhodamine B.
Abstract: The exploration of new porous hybrid materials is of great importance because of their unique properties and promising applications in separation of materials, catalysis, etc. Herein, for the first time, by integration of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), a new type of MOF@COF core-shell hybrid material, i.e., NH2 -MIL-68@TPA-COF, with high crystallinity and hierarchical pore structure, is synthesized. As a proof-of-concept application, the obtained NH2 -MIL-68@TPA-COF hybrid material is used as an effective visible-light-driven photocatalyst for the degradation of rhodamine B. The synthetic strategy in this study opens up a new avenue for the construction of other MOF-COF hybrid materials, which could have various promising applications.
TL;DR: This review focuses on the most recent important discoveries in the preparation, characterization and application of these new-structured ultrathin 2D layered TMDs.
Abstract: Ultrathin two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have attracted considerable attention owing to their unique properties and great potential in a wide range of applications. Great efforts have been devoted to the preparation of novel-structured TMD nanosheets by engineering their intrinsic structures at the atomic scale. Until now, a lot of new-structured TMD nanosheets, such as vacancy-containing TMDs, heteroatom-doped TMDs, TMD alloys, 1T′/1T phase and in-plane TMD crystal-phase heterostructures, TMD heterostructures and Janus TMD nanosheets, have been prepared. These materials exhibit unique properties and hold great promise in various applications, including electronics/optoelectronics, thermoelectrics, catalysis, energy storage and conversion and biomedicine. This review focuses on the most recent important discoveries in the preparation, characterization and application of these new-structured ultrathin 2D layered TMDs.
01 Jun 2018
TL;DR: In this paper, the authors show that the lithiation-induced amorphization of layered crystalline Pd3P2S8 activates this otherwise electrochemically inert material as a highly efficient hydrogen evolution catalyst.
Abstract: Engineering material structures at the atomic level is a promising way to tune the physicochemical properties of materials and optimize their performance in various potential applications. Here, we show that the lithiation-induced amorphization of layered crystalline Pd3P2S8 activates this otherwise electrochemically inert material as a highly efficient hydrogen evolution catalyst. Electrochemical lithiation of the layered Pd3P2S8 crystal results in the formation of amorphous lithium-incorporated palladium phosphosulfide nanodots with abundant vacancies. The structure change during the lithiation-induced amorphization process is investigated in detail. The amorphous lithium-incorporated palladium phosphosulfide nanodots exhibit excellent electrocatalytic activity towards the hydrogen evolution reaction with an onset potential of −52 mV, a Tafel slope of 29 mV dec−1 and outstanding long-term stability. Experimental and theoretical investigations reveal that the tuning of morphology and structure of Pd3P2S8 (for example, dimension decrease, crystallinity loss, vacancy formation and lithium incorporation) contribute to the activation of its intrinsically inert electrocatalytic property. This work provides a unique way for structure tuning of a material to effectively manipulate its catalytic properties and functionalities. The structural modification of inactive materials to effectively engineer active catalysts is very attractive. Here, layered crystalline Pd3P2S8 is transformed by electrochemical lithiation into amorphous Li-incorporated nanodots. This process turns the inert parent material into a highly active and stable hydrogen-evolving catalyst.
TL;DR: This synthesized crystal-phase heterostructured 4H/fcc Au nanowires are used as seeds to epitaxially grow a variety of binary and ternary hybrid noble metal nanostructures on the phase boundary, resulting in hybrid Au–Runanowires.
Abstract: Crystal-phase engineering offers opportunities for the rational design and synthesis of noble metal nanomaterials with unusual crystal phases that normally do not exist in bulk materials. However, it remains a challenge to use these materials as seeds to construct heterometallic nanostructures with desired crystal phases and morphologies for promising applications such as catalysis. Here, we report a strategy for the synthesis of binary and ternary hybrid noble metal nanostructures. Our synthesized crystal-phase heterostructured 4H/fcc Au nanowires enable the epitaxial growth of Ru nanorods on the 4H phase and fcc-twin boundary in Au nanowires, resulting in hybrid Au-Ru nanowires. Moreover, the method can be extended to the epitaxial growth of Rh, Ru-Rh and Ru-Pt nanorods on the 4H/fcc Au nanowires to form unique hybrid nanowires. Importantly, the Au-Ru hybrid nanowires with tunable compositions exhibit excellent electrocatalytic performance towards the hydrogen evolution reaction in alkaline media.
TL;DR: Through a one-pot wet-chemical method, a series of amorphous/crystalline hetero-phase Pd nanosheets is synthesized with different crystallinities for the catalytic 4-nitrostyrene hydrogenation, and the chemoselectivity and activity can be fine-tuned by controlling the crystallinity of the as-synthesized Pd Nanosheet.
Abstract: Similar to heterostructures composed of different materials, possessing unique properties due to the synergistic effect between different components, the crystal-phase heterostructures, one variety of hetero-phase structures, composed of different crystal phases in monometallic nanomaterials are herein developed, in order to explore crystal-phase-based applications. As novel hetero-phase structures, amorphous/crystalline heterostructures are highly desired, since they often exhibit unique properties, and hold promise in various applications, but these structures have rarely been studied in noble metals. Herein, via a one-pot wet-chemical method, a series of amorphous/crystalline hetero-phase Pd nanosheets is synthesized with different crystallinities for the catalytic 4-nitrostyrene hydrogenation. The chemoselectivity and activity can be fine-tuned by controlling the crystallinity of the as-synthesized Pd nanosheets. This work might pave the way to preparing various hetero-phase nanostructures for promising applications.
TL;DR: This work provides a new strategy for the synthesis of highly anisotropic superstructures with a spatial heterogeneity to boost their promising application in catalytic reactions.
Abstract: The rational design and synthesis of anisotropic 3D nanostructures with specific composition, morphology, surface structure, and crystal phase is of significant importance for their diverse applications. Here, the synthesis of well-crystalline lotus-thalamus-shaped Pt-Ni anisotropic superstructures (ASs) via a facile one-pot solvothermal method is reported. The Pt-Ni ASs with Pt-rich surface are composed of one Ni-rich "core" with face-centered cubic (fcc) phase, Ni-rich "arms" with hexagonal close-packed phase protruding from the core, and facet-selectively grown Pt-rich "lotus seeds" with fcc phase on the end surfaces of the "arms." Impressively, these unique Pt-Ni ASs exhibit superior electrocatalytic activity and stability toward the hydrogen evolution reaction under alkaline conditions compared to commercial Pt/C and previously reported electrocatalysts. The obtained overpotential is as low as 27.7 mV at current density of 10 mA cm-2 , and the turnover frequency reaches 18.63 H2 s-1 at the overpotential of 50 mV. This work provides a new strategy for the synthesis of highly anisotropic superstructures with a spatial heterogeneity to boost their promising application in catalytic reactions.
TL;DR: The research progress regarding the fine control of noble metal and non-noble metal nanomaterials with novel crystal phases and the challenges and perspectives in this emerging field are proposed.
Abstract: 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.
TL;DR: It is found that Pb and Cd contributed to the greatest health risk and leafy vegetables tend to be more contaminated than non-leafy vegetables.
TL;DR: In recognition of the leading role played by graphene and TMDs which has been well summarized in many review articles or themed issues, this themed issue is entitled 2D nanomaterials: beyond graphene and transition metal dichalcogenides.
Abstract: Graphene and transition metal dichalcogenides (TMDs), as typical two-dimensional (2D) nanomaterials, have impressed the research community owing to their unique structural features, fascinating physiochemical properties, and promising applications in diverse fields. More significantly, the success of graphene and TMDs has inspired researchers to explore many other 2D nanomaterials. Though possessing a similar sheet-like structure as graphene and TMDs, these 2D nanomaterials can own strikingly different properties, rendering them attractive in various research and application fields. The past years have witnessed the blossom and tremendous progress in studies of novel 2D nanomaterials beyond graphene and TMDs. In view of this, it is time to provide a themed issue, with a compilation of excellent review articles, covering a wide range of 2D nanomaterials. In recognition of the leading role played by graphene and TMDs which has been well summarized in many review articles or themed issues, this themed issue is entitled 2D nanomaterials: beyond graphene and transition metal dichalcogenides.
TL;DR: By combining chemical vapor transport and Li-intercalation, a series of 1T'-phase ReS2 xSe2(1- x) ( x = 0-1) nanodots are prepared to achieve high-performance HER in acid medium, with the highest hydrogen evolution activity.
Abstract: As a source of clean energy, a reliable hydrogen evolution reaction (HER) requires robust and highly efficient catalysts. Here, by combining chemical vapor transport and Li-intercalation, we have prepared a series of 1T′-phase ReS2xSe2(1-x) (x = 0–1) nanodots to achieve high-performance HER in acid medium. Among them, the 1T′-phase ReSSe nanodot exhibits the highest hydrogen evolution activity, with a Tafel slope of 50.1 mV dec–1 and a low overpotential of 84 mV at current density of 10 mA cm–2. The excellent hydrogen evolution activity is attributed to the optimal hydrogen absorption energy of the active site induced by the asymmetric S vacancy in the highly asymmetric 1T′ crystal structure.
TL;DR: This themed issue attempts to present recent progress in studies related to 2D materials, covering a wide array of topics, and presents recent achievements and challenges related to the chemical vapor deposition (CVD) growth method.
Abstract: T topic of this thematic issue is two-dimensional (2D) materials. The field has exploded since 2004, when graphene was successfully prepared from graphite by mechanical exfoliation with Scotch tape by Novoselov, Geim, and co-workers. In the subsequent decade-and-a-half the scientific community has shown great enthusiasm for studying graphene and graphene-analogous 2D materials, including the transition metal dichalcogenides (TMDs), graphitic carbon nitride (g-C3N4), hexagonal boron nitride (h-BN), black phosphorus (BP), MXenes, silicene, etc. Their fascinating physical, electronic, optical, and chemical properties as well as the promise of new applications arising from these properties have enchanted researchers from diverse fields such as condensed matter physics, materials science, chemistry, and nanotechnology. For example, the electron confinement in two dimensions confers 2D materials with intriguing electronic properties, which has stimulated the development of nextgeneration electronic devices. In addition, the large specific surface area of 2D materials motivates their use in surface-active applications, such as catalysis and sensing. Furthermore, their atomic thickness and high anisotropy endow 2D materials with excellent mechanical flexibility and optical transparency, which provide great opportunities for developing 2D material-based (opto-)electronic devices and wearable devices. In addition, disparate 2D materials can be assembled to form heterostructures without the constraints of lattice matching and processing compatibility, offering synergistic effects which benefit a wide spectrum of applications. Despite the exciting achievements in the field of 2D materials, challenges still exist. Large-scale production of 2D materials with high quality and controlled structure has yet to be realized for ultimate industrialization. Furthermore, obtaining precise control over their compositions, thicknesses, lateral sizes, crystal phases, doping, defects, strains, vacancies, and surface properties is of paramount importance to unveil the correlation between their structural features and properties. In addition, inspired by the significant progress in layered 2D materials, other types of nanomaterials with two dimensionality are believed to exhibit fascinating properties, such as 2D metal nanomaterials and 2D perovskites, which deserve more research focus. With the current achievements and the nonstop efforts from various research fields, it seems inevitable that we will reach the major milestone when the commercialization of 2D materials in our daily life is finally realized. Targeting at these goals, this themed issue attempts to present recent progress in studies related to 2D materials, covering a wide array of topics. The following reviews are published in this themed issue. Hui-Ming Cheng and co-workers (DOI: 10.1021/acs.chemrev.7b00536) present recent achievements and challenges related to the chemical vapor deposition (CVD) growth method. Specifically, they review three categories of materials prepared by the CVD method. They first summarize the CVD growth of single-crystal 2D materials with control over their grain sizes, layer, orientation, morphologies, phases, doping, and defects. Then the CVD growth of wafer-scale continuous 2D material films on rigid and flexible substrates is overviewed. Besides, the CVD growth of 2D material-based heterostructures including vertical, lateral, and other dimension/2D heterostructures is elaborated. Finally, various applications and challenges related to the CVD-grown 2D materials and their heterostructures are discussed. Lain-Jong Li and co-workers (DOI: 10.1021/acs.chemrev.7b00212) provide a review over the preparation of 2D TMDs and their heterostructures by the CVD growth method, highlighting its capability to produce high-quality TMD layers with scalable size, controllable thickness, and excellent electronic properties. To emphasize, they thoroughly explain the growth mechanisms of TMDs, thus providing guidelines for precise control over their structures and properties by the CVD method. Jinwoo Cheon and co-workers (DOI: 10.1021/acs.chemrev.8b00264) review recent advances in the solution-based preparation of 2D layered TMDs. They highlight the advantages of the solution-based synthetic strategies, such as controllability over size and composition at the molecular level, scalability, competitive production cost, and solution processability. Xinliang Feng and co-workers (DOI: 10.1021/acs.chemrev.8b00056) focus on the utilization of an interface-assisted synthetic approach to prepare inorganic and organic 2D materials. They emphasize the advantages and uniqueness of the interfacial synthetic methods, especially highlighting their controllability over the structures, morphologies, and crystal phases via directing the arrangement of the molecules or precursors at a confined 2D space. Further, different interfacial synthetic strategies and the as-prepared inorganic and organic 2D materials are summarized, along with some recommended characterization techniques for better understanding their growth mechanisms. Lei Fu and co-workers (DOI: 10.1021/acs.chemrev.7b00633) review recent advances of 2D materials in terms of their monomer design and assembly control. They categorize different types of 2D materials and highlight various physical and chemical strategies to design their monomers with control over their dimensions, compositions, and structures. Furthermore, they highlight diverse assembly strategies of these 2D materials monomers into mass or ordered heterostructures. The applications of these 2D materials in next-generation electronics are overviewed as well. Young Hee Lee and co-workers (DOI: 10.1021/acs.chemrev.7b00618) present works related to van der Waals layered TMDs. They especially focus on different structural phases of layered TMDs, including metallic and semiconducting TMDs. Diverse phase transformation strategies and the dependence of electronic structures on different phases are discussed. Furthermore, various synthetic methods with capability of
TL;DR: This work reports on snap-buckling motivated jumping of thermoresponsive hydrogel bilayers and paves a novel way for the rapid actuation of responsive hydrogels in a controlled manner and may stimulate the development of novelhydrogel devices.
Abstract: Responsive hydrogel actuators have promising applications in diverse fields. Most hydrogel actuators are limited by slow actuation or shape transformations. This work reports on snap-buckling motivated jumping of thermoresponsive hydrogel bilayers. The bilayers are composed of poly(NIPAM-co-DMAPMA)/clay hydrogel with different lower critical solution temperatures in each layer, and thus undergo slow reversible curling/uncurling at temperature changes. The gels are adhesive to numerous materials including aluminum. The adhesion between the gels and an aluminum ratchet is utilized to constrain the thermoresponsive deformation of the bilayers to store elastic energy. When the accumulated elastic energy overwhelms the gel–aluminum adhesion, snap-buckling takes place to abruptly release the accumulated energy, which motivates the bilayer to jump. The jumping direction, start time, height, and distance are controlled by the geometry of the bilayers or the ratchet. This work paves a novel way for the rapid actua...
TL;DR: In this paper, a flexible piezoresistive strain sensor was demonstrated using laser thermal reduced graphene oxide doped with polystyrene nanoparticles, which significantly increased the resistance change under strain.
TL;DR: As an electrocatalyst for the hydrogen evolution reaction in alkaline media, the hierarchical 4H/fcc Ru NTs exhibit excellent electrocatalytic performance, which is better than 4H /face-centered cubic Au-Ru NWs, commercial Pt/C, Ru-Ru, and most of the reported Electrocatalysts.
Abstract: Hierarchical metal nanostructures containing 1D nanobuilding blocks have stimulated great interest due to their abundant active sites for catalysis. Herein, hierarchical 4H/face-centered cubic (fcc) Ru nanotubes (NTs) are synthesized by a hard template-mediated method, in which 4H/fcc Au nanowires (NWs) serve as sacrificial templates which are then etched by copper ions (Cu2+ ) in dimethylformamide. The obtained hierarchical 4H/fcc Ru NTs contain ultrathin Ru shells (5-9 atomic layers) and tiny Ru nanorods with length of 4.2 ± 1.1 nm and diameter of 2.2 ± 0.5 nm vertically decorated on the surface of Ru shells. As an electrocatalyst for the hydrogen evolution reaction in alkaline media, the hierarchical 4H/fcc Ru NTs exhibit excellent electrocatalytic performance, which is better than 4H/fcc Au-Ru NWs, commercial Pt/C, Ru/C, and most of the reported electrocatalysts.
TL;DR: It is shown that at room temperature, light illumination can modulate the CDW phase and thus tune the frequency of the ultrathin 1T-TaS2 oscillators, providing a better understanding of the electric field-induced phase transition.
Abstract: External stimuli-controlled phase transitions are essential for fundamental physics and design of functional devices. Charge density wave (CDW) is a metastable collective electronic phase featured by the periodic lattice distortion. Much attention has been attracted to study the external control of CDW phases. Although much work has been done in the electric-field-induced CDW transition, the study of the role of Joule heating in the phase transition is insufficient. Here, using the Raman spectroscopy, the electric-field-driven phase transition is in situ observed in the ultrathin 1T-TaS2. By quantitative evaluation of the Joule heating effect in the electric-field-induced CDW transition, it is shown that Joule heating plays a secondary role in the nearly commensurate (NC) to incommensurate (IC) CDW transition, while it dominants the IC-NC CDW transition, providing a better understanding of the electric field-induced phase transition. More importantly, at room temperature, light illumination can modulate t...
TL;DR: This work demonstrates the use of polymer shells as adjustable masks for nanosynthesis, where the different modes of shell transformation allow unconventional designs beyond facet control, allowing versatile and multi-step functionalization of colloidal particles at selective locations.
Abstract: Synthetic skills are the prerequisite and foundation for the modern chemical and pharmaceutical industry. The same is true for nanotechnology, whose development has been hindered by the sluggish advance of its synthetic toolbox, i.e., the emerging field of nanosynthesis. Unlike organic chemistry, where the variety of functional groups provides numerous handles for designing chemical selectivity, colloidal particles have only facets and ligands. Such handles are similar in reactivity to each other, limited in type, symmetrically positioned, and difficult to control. In this work, we demonstrate the use of polymer shells as adjustable masks for nanosynthesis, where the different modes of shell transformation allow unconventional designs beyond facet control. In contrast to ligands, which bind dynamically and individually, the polymer masks are firmly attached as sizeable patches but at the same time are easy to manipulate, allowing versatile and multi-step functionalization of colloidal particles at selective locations.
TL;DR: This work reports the irreversible transformation from the hexagonal 4H to face-centered cubic ( fcc) phase in Au nanoribbons (NRBs) through high pressure treatment, which has not been discovered in metals.
Abstract: Although phase engineering of a noble metal, gold (Au), is of critical importance for both fundamental research and potential application, it still remains a big challenge in wet-chemical syntheses. In this work, we report the irreversible transformation from the hexagonal 4H to face-centered cubic (fcc) phase in Au nanoribbons (NRBs) through high pressure treatment, which has not been discovered in metals. The relative percentage of 4H and fcc phases in the recovered Au NRBs depends directly on the peak pressure applied to the original 4H Au NRBs, enabling a phase engineering of Au nanostructures. Interestingly, compared to the pure 4H Au NRBs, the crystal-phase-heterostructured 4H/fcc Au nanorods require less energy to complete the phase transition process with a lower transition pressure and in a narrower range. Finally, the atom-based transformation pathway during the 4H-to-fcc phase transition is revealed experimentally, which is supported by the first-principle calculations. This work not only demon...