25th Anniversary Article: Hybrid Nanostructures Based on Two‐Dimensional Nanomaterials

Two‐dimensional (2D) nanomaterials, such as graphene and transition metal dichalcogenides (TMDs), receive a lot of attention, because of their intriguing properties and wide applications in catalysis, energy‐storage devices, electronics, optoelectronics, and so on. To further enhance the performance of their application, these 2D nanomaterials are hybridized with other functional nanostructures. In this review, the latest studies of 2D nanomaterial‐based hybrid nanostructures are discussed, focusing on their preparation methods, properties, and applications.     

Two‐Dimensional Nanomaterials for Cancer Nanotheranostics

Emerging nanotechnologies show unprecedented advantages in accelerating cancer theranostics. Among them, two‐dimensional nanomaterials (2DNMs) represent a novel type of material with versatile physicochemical properties that have enabled a new horizon for applications in both cancer diagnosis and therapy. Studies have demonstrated that 2DNMs may be used in diverse aspects, including i) cancer detection due to their high propensity towards tumor markers; ii) molecular imaging for guided tumor therapies, and iii) drug and gene loading, photothermal and photodynamic cancer therapies. However, their biomedical applications raise concerns due to the limited understanding of their in vivo metabolism, transformation and possible toxicities. In this comprehensive review, the state‐of‐the‐art development of 2DNMs and their implications for cancer nanotheranostics are presented. The modification strategies to enhance the biocompatibility of 2DNMs are also reviewed.     

Production of Two‐Dimensional Nanomaterials via Liquid‐Based Direct Exfoliation

Tremendous efforts have been devoted to the synthesis and application of two‐dimensional (2D) nanomaterials due to their extraordinary and unique properties in electronics, photonics, catalysis, etc., upon exfoliation from their bulk counterparts. One of the greatest challenges that scientists are confronted with is how to produce large quantities of 2D nanomaterials of high quality in a commercially viable way. This review summarizes the state‐of‐the‐art of the production of 2D nanomaterials using liquid‐based direct exfoliation (LBE), a very promising and highly scalable wet approach for synthesizing high quality 2D nanomaterials in mild conditions. LBE is a collection of methods that directly exfoliates bulk layered materials into thin flakes of 2D nanomaterials in liquid media without any, or with a minimum degree of, chemical reactions, so as to maintain the high crystallinity of 2D nanomaterials. Different synthetic methods are categorized in the following, in which material characteristics including dispersion concentration, flake thickness, flake size and some applications are discussed in detail. At the end, we provide an overview of the advantages and disadvantages of such synthetic methods of LBE and propose future perspectives.     

Ultrathin Two‐Dimensional Multinary Layered Metal Chalcogenide Nanomaterials

Ultrathin two‐dimensional (2D) layered transition metal dichalcogenides (TMDs), such as MoS₂, WS₂, TiS₂, TaS₂, ReS₂, MoSe₂ and WSe₂, have attracted considerable attention over the past six years owing to their unique properties and great potential in a wide range of applications. Aiming to achieve tunable properties and optimal application performances, great effort is devoted to the exploration of 2D multinary layered metal chalcogenide nanomaterials, which include ternary metal chalcogenides with well‐defined crystal structures, alloyed TMDs, heteroatom‐doped TMDs and 2D metal chalcogenide heteronanostructures. These novel 2D multinary layered metal chalcogenide nanomaterials exhibit some unique properties compared to 2D binary TMD counterparts, thus holding great promise in various potential applications including electronics/optoelectronics, catalysis, sensors, biomedicine, and energy storage and conversion with enhanced performances. This article focuses on the state‐of‐art progress on the preparation, characterization and applications of ultrathin 2D multinary layered metal chalcogenide nanomaterials.     

One Dimensional Silver‐based Nanomaterials: Preparations and Electrochemical Applications

One dimensional (1D) silver‐based nanomaterials have a great potential in various fields because of their high specific surface area, high electric conductivity, optoelectronic properties, mechanical flexibility and high electro‐catalytic efficiency. In this Review, the preparations of 1D silver‐based nanomaterials is classified by structure composed of simple silver nanowires/rods/belts/tubes, core‐shells, and hybrids. The latest applications based on 1D silver nanomaterials and their composite materials are summarized systematically including electrochemical capacitors, lithium‐ion/lithium‐oxygen batteries, electrochemical sensors and electrochemical catalysis. The preparation process, tailored material properties and electrochemical applications are discussed.     

Recent Advances in Synthesis and Biomedical Applications of Two‐Dimensional Transition Metal Dichalcogenide Nanosheets

During recent decades, a giant leap in the development of nanotechnology has been witnessed. Numerous nanomaterials with different dimensions and unprecedented features have been developed and provided unimaginably wide scope to solve the challenging problems in biomedicine, such as cancer diagnosis and therapy. Recently, two‐dimensional (2D) transition metal dichalcogenide (TMDC) nanosheets (NSs), including MoS₂, WS₂, and etc., have emerged as novel inorganic graphene analogues and attracted tremendous attention due to their unique structures and distinctive properties, and opened up great opportunities for biomedical applications, including ultrasensitive biosensing, biological imaging, drug delivery, cancer therapy, and antibacterial treatment. A comprehensive overview of different synthetic methods of ultrathin 2D TMDC NSs and their state‐of‐the‐art biomedical applications, especially those that have appeared in the past few years, is presented. At the end of this review, the future opportunities and challenges for 2D TMDC NSs in biomedicine are also discussed.     

类石墨烯结构二维氮化硼材料:结构特性、合成方法、性能及应用

石墨烯的发现和成功制备引起了人们对二维材料的研究热潮。六方氮化硼(h-BN)薄膜作为类石墨烯结构的二维层状材料,也是当前的研究热点。介绍了h-BN及其相应的低维纳米结构,并概述了近期对二维BN纳米材料的形貌、合成、性能和应用的研究进展。目前对一维和二维纳米材料的研究表明,BN纳米材料具有诸多优异性能,包括高温稳定性、低介电常数、高力学性能、高热导率、高硬度和高耐腐蚀性,BN纳米材料系统已成为最具前景的非碳纳米系统,在不远的将来将有广泛的应用。     

Exploring Two‐Dimensional Transport Phenomena in Metal Oxide Heterointerfaces for Next‐Generation,High‐Performance,Thin‐Film Transistor Technologies

In the last decade, metal oxides have emerged as a fascinating class of electronic material, exhibiting a wide range of unique and technologically relevant characteristics. For example, thin‐film transistors formed from amorphous or polycrystalline metal oxide semiconductors offer the promise of low‐cost, large‐area, and flexible electronics, exhibiting performances comparable to or in excess of incumbent silicon‐based technologies. Atomically flat interfaces between otherwise insulating or semiconducting complex oxides, are also found to be highly conducting, displaying 2‐dimensional (2D) charge transport properties, strong correlations, and even superconductivity. Field‐effect devices employing such carefully engineered interfaces are hoped to one day compete with traditional group IV or III–V semiconductors for use in the next‐generation of high‐performance electronics. In this Concept article we provide an overview of the different metal oxide transistor technologies and potential future research directions. In particular, we look at the recent reports of multilayer oxide thin‐film transistors and the possibility of 2D electron transport in these disordered/polycrystalline systems and discuss the potential of the technology for applications in large‐area electronics.     

Vacancy‐Driven Gelation Using Defect‐Rich Nanoassemblies of 2D Transition Metal Dichalcogenides and Polymeric Binder for Biomedical Applications

A new approach of vacancy‐driven gelation to obtain chemically crosslinked hydrogels from defect‐rich 2D molybdenum disulfide (MoS₂) nanoassemblies and polymeric binder is reported. This approach utilizes the planar and edge atomic defects available on the surface of the 2D MoS₂ nanoassemblies to form mechanically resilient and elastomeric nanocomposite hydrogels. The atomic defects present on the lattice plane of 2D MoS₂ nanoassemblies are due to atomic vacancies and can act as an active center for vacancy‐driven gelation with a thiol‐activated terminal such as four‐arm poly(ethylene glycol)–thiol (PEG‐SH) via chemisorption. By modulating the number of vacancies on the 2D MoS₂ nanoassemblies, the physical and chemical properties of the hydrogel network can be controlled. This vacancy‐driven gelation process does not require external stimuli such as UV exposure, chemical initiator, or thermal agitation for crosslinking and thus provides a nontoxic and facile approach to encapsulate cells and proteins. 2D MoS₂ nanoassemblies are cytocompatible, and encapsulated cells in the nanocomposite hydrogels show high viability. Overall, the nanoengineered hydrogel obtained from vacancy‐driven gelation is mechanically resilient and can be used for a range of biomedical applications including tissue engineering, regenerative medicine, and cell and therapeutic delivery.     

超级电容器中的二维材料

以石墨烯为代表的具有层状结构的二维材料因具有大比表面积等特性成为超级电容器电极材料的热门候选。文章着眼于针对诸如石墨烯、过渡金属二硫族化合物、过渡金属碳/氮化物、层状过渡金属氧化物/氢氧化物等二维材料在超级电容器领域应用的研究,尝试总结了其制备方法、产物形貌特征以及作为电极的性能等,并对这一领域的未来发展和面临的挑战提出了看法与预测。     

Phosphorene and Phosphorene‐Based Materials – Prospects for Future Applications

Phosphorene, a single‐ or few‐layered semiconductor material obtained from black phosphorus, has recently been introduced as a new member of the family of two‐dimensional (2D) layered materials. Since its discovery, phosphorene has attracted significant attention, and due to its unique properties, is a promising material for many applications including transistors, batteries and photovoltaics (PV). However, based on the current progress in phosphorene production, it is clear that a lot remains to be explored before this material can be used for these applications. After providing a comprehensive overview of recent advancements in phosphorene synthesis, advantages and challenges of the currently available methods for phosphorene production are discussed. An overview of the research progress in the use of phosphorene for a wide range of applications is presented, with a focus on enabling important roles that phosphorene would play in next‐generation PV cells. Roadmaps that have the potential to address some of the challenges in phosphorene research are examined because it is clear that the unprecedented chemical, physical and electronic properties of phosphorene and phosphorene‐based materials are suitable for various applications, including photovoltaics.     

Oxidative Intercalation for Monometallic Ni2+‐Ni3+ Layered Double Hydroxide and Enhanced Capacitance in Exfoliated Nanosheets

Monometallic Ni²⁺‐Ni³⁺ layered double hydroxide (LDH) is prepared using a simple oxidative intercalation process and may be further exfoliated into positively charged Ni(OH)₂ unilamellar sheets. The superior capacitive behavior of the unilamellar sheets stranded in carbon nanotubes (CNTs) networks is achieved because of the complete interfacial charge storage arising from the confined Faradaic reactions at the interfacial region. 3D nanosheet/CNT composites are prepared using an in situ electrostatic assembly of positive charged sheets with CNTs bearing negative charges. The restacking of active nanosheets during electrochemical cycling is effectively prohibited. Consequently, the outstanding specific capacitance and remarkable rate capability of the nanosheet/CNT hybrid electrodes are demonstrated, making them promising candidates for high performance supercapacitors, combining high‐energy storage densities with high levels of power delivery.     

Photoluminescence Architectures for Disease Diagnosis: From Graphene to Thin‐Layer Transition Metal Dichalcogenides and Oxides

Ever since the discovery of graphene, increasing efforts have been devoted to the use of this stellar material as well as the development of other graphene‐like materials such as thin‐layer transition metal dichalcogenides and oxides (TMD/Os) for a variety of applications. Because of their large surface area and unique optical properties, these two‐dimensional materials with a size ranging from the micro‐ to the nanoscale have been employed as the substrate to construct photoluminescence architectures for disease diagnosis as well as theranostics. These architectures are built through the simple self‐assembly of labeled biomolecular probes with the substrate material, leading to signal quenching. Upon the specific interaction of the architecture with a target biomarker, the signal can be spontaneously restored in a reversible manner. Meanwhile, by co‐loading therapeutic agents and employing the inherent photo‐thermal properties of the material substrates, a combined disease imaging and therapy (theranostics) can be achieved. This review highlights the latest advances in the construction and application of graphene and TMD/O based thin‐layer material composites for single‐target and multiplexed detection of a variety of biomarkers and theranostics. These versatile material architectures, owing to their ease in preparation, low cost and flexibility in functionalization, provide promising tools for both basic biochemical research and clinical applications.     

2D Transition‐Metal‐Dichalcogenide‐Nanosheet‐Based Composites for Photocatalytic and Electrocatalytic Hydrogen Evolution Reactions

Hydrogen (H₂) is one of the most important clean and renewable energy sources for future energy sustainability. Nowadays, photocatalytic and electrocatalytic hydrogen evolution reactions (HERs) from water splitting are considered as two of the most efficient methods to convert sustainable energy to the clean energy carrier, H₂. Catalysts based on transition metal dichalcogenides (TMDs) are recognized as greatly promising substitutes for noble‐metal‐based catalysts for HER. The photocatalytic and electrocatalytic activities of TMD nanosheets for the HER can be further improved after hybridization with many kinds of nanomaterials, such as metals, oxides, sulfides, and carbon materials, through different methods including the in situ reduction method, the hot‐injection method, the heating‐up method, the hydro(solvo)thermal method, chemical vapor deposition (CVD), and thermal annealing. Here, recent progress in photocatalytic and electrocatalytic HERs using 2D TMD‐based composites as catalysts is discussed.     

Remeshing for metal forming simulations—Part I: Two‐dimensional quadrilateral remeshing

In this paper, a general framework of practical two‐dimensional quadrilateral remeshing, which includes the determination of remeshing time, automatic quadrilateral mesh generation, and data transfer process, will be formulated. In particular, the current work contains new algorithms of mesh density specification according to the distribution of effective strain‐rate gradients, mesh density smoothing by fast Fourier transform (FFT) and low‐pass filtering techniques, coarsening it by node placement scheme, and a modified Laplacian mesh smoothing technique. The efficiency of the developed remeshing scheme was tested through three practical two‐dimensional metal forming simulations. The results clearly indicate that the algorithms proposed in this study make it possible to simulate two‐dimensional metal forming problems efficiently and automatically. Copyright © 2002 John Wiley & Sons, Ltd.     

Hybridizing Plasmonic Materials with 2D‐Transition Metal Dichalcogenides toward Functional Applications

Recently, 2D transition metal dichalcogenides (TMDs) have become intriguing materials in the versatile field of photonics and optoelectronics because of their strong light–matter interaction that stems from the atomic layer thickness, broadband optical response, controllable optoelectronic properties, and high nonlinearity, as well as compatibility. Nevertheless, the low optical cross‐section of 2D‐TMDs inhibits the light–matter interaction, resulting in lower quantum yield. Therefore, hybridizing the 2D‐TMDs with plasmonic nanomaterials has become one of the promising strategies to boost the optical absorption of thin 2D‐TMDs. The appeal of plasmonics is based on their capability to localize and enhance the electromagnetic field and increase the optical path length of light by scattering and injecting hot electrons to TMDs. In this regard, recent achievements with respect to hybridization of the plasmonic effect in 2D‐TMDs systems and its augmented optical and optoelectronic properties are reviewed. The phenomenon of plasmon‐enhanced interaction in 2D‐TMDs is briefly described and state‐of‐the‐art hybrid device applications are comprehensively discussed. Finally, an outlook on future applications of these hybrid devices is provided.     

Multishelled Transition Metal‐Based Microspheres: Synthesis and Applications for Batteries and Supercapacitors

With the rapid growth of material innovations, multishelled hollow nanostructures are of tremendous interest due to their unique structural features and attractive physicochemical properties. Continued effort has been made in the geometric manipulation, composition complexity, and construction diversity of this material, expanding its applications. Energy storage technology has benefited from the large surface area, short transport path, and excellent buffering ability of the nanostructures. In this work, the general synthesis of multishelled hollow structures, especially with architecture versatility, is summarized. A wealth of attractive properties is also discussed for a wide area of potential applications based on energy storage systems, including Li‐ion/Na‐ion batteries, supercapacitors, and Li–S batteries. Finally, the emerging challenges and outlook for multishelled hollow structures are mentioned.