Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

Metal-organic frameworks (MOFs), an important class of inorganic-organic hybrid crystals with intrinsic porous structures, can be used as versatile precursors or sacrificial templates for preparation of numerous functional nanomaterials for various applications. Recent developments of MOF-derived hybrid micro-/nano-structures, constructed by more than two components with varied functionalities, have revealed their extensive capabilities to overcome the weaknesses of the individual counterparts and thus give enhanced performance for energy storage and conversion. In this tutorial review, we summarize the recent advances in MOF-derived hybrid micro-/nano-structures. The synthetic strategies for preparing MOF-derived hybrid micro-/nano-structures are first introduced. Focusing on energy storage and conversion, we then discuss their potential applications in lithium-ion batteries, lithium-sulfur batteries, supercapacitors, lithium-oxygen batteries and fuel cells. Finally, we give our personal insights into the challenges and opportunities for the future research of MOF-derived hybrid micro-/nano-structures.

Colloidal metal-organic frameworks (CMOFs), nanoporous colloidal-sized crystals that are uniform in both size and polyhedral shape, are crystals composed of metal ions and organic bridging ligands, which can be used as building blocks for self-assembly in organic and aqueous liquids. They stand in contrast to conventional metal-organic frameworks (MOFs), which scientists normally study in the form of bulk crystalline powders. However, powder MOFs generally have random crystal size and shape and therefore do not possess either a definite mutual arrangement with adjacent particles or uniformity. CMOFs do have this quality, which can be important in vital uptake and release kinetics. In this Account, we present the diverse methods of synthesis, pore chemistry control, surface modification, and assembly techniques of CMOFs. In addition, we survey recent achievements and future applications in this emerging field. There is potential for a paradigm shift, away from using just bulk crystalline powders, towards using particles whose size and shape are regulated. The concept of colloidal MOFs takes into account that nanoporous MOFs, conventionally prepared in the form of bulk crystalline powders with random crystal size, shape, and orientation, may also form colloidal-sized objects with uniform size and morphology. Furthermore, the traditional MOF functions that depend on porosity present additional control over those MOF functions that depend on pore interactions. They also can enable controlled spatial arrangements between neighboring particles. To begin, we discuss progress regarding synthesis of MOF nano- and microcrystals whose crystal size and shape are well regulated. Next, we review the methods to modify the surfaces with dye molecules and polymers. Dyes are useful when seeking to observe nonluminescent CMOFs in situ by optical microscopy, while polymers are useful to tune their interparticle interactions. Third, we discuss criteria to assess the stability of CMOFs for various applications. In another section of this Account, we give examples of supracrystal assembly in liquid, on substrates, at interfaces, and under external electric fields. We end this Account with discussion of possible future developments, both conceptual and technological.

Monodisperse polyhedral metal-organic framework (MOF) particles up to 5 μm in size, large enough to enable in situ optical imaging of particle orientation, were synthesized by the strategy of simultaneous addition of two capping ligands with different binding strength during crystallization. Upon dispersing them in ethylene glycol and applying AC electric field, the particles facets link to form linear chains. We observe well-regulated crystal orientation not only for rhombic dodecahedra all of whose facets are equivalent, but also for truncated cubes with nondegenerate facets. After removing the electric field, chains disassemble if their facets contain even modest curvature, but remain intact if their facets are planar. This assembly strategy offers a general route to fabricate oriented polyhedral crystal arrays of potential interest for new applications and functions.

Inspired by the unique properties of ultrathin 2D nanomaterials and excellent catalytic activities of noble metal nanostructures for renewable fuel cells, a facile method is reported for the high-yield synthesis of ultrathin 2D PdCu alloy nanosheets under mild conditions. Impressively, the obtained PdCu alloy nanosheet after being treated with ethylenediamine can be used as a highly efficient electrocatalyst for formic acid oxidation. The study implicates that the rational design and controlled synthesis of an ultrathin 2D noble metal alloy may open up new opportunities for enhancing catalytic activities of noble metal nanostructures.

of 18) 1605817As a newly emerging class of nanomaterials, 2D TMD nanosheets possess a unique layered structure and large surface areas, as well as outstanding physical, chemical, optical, and electronic properties, which holds great potential for applications in catalysis, [37] sensing, [38] optics, [39] and energy. [40] In this review, we will focus on the introduction of state of the art sensing applications for 2D TMD nanosheets and their composites. In particular, different sensing strategies together with signal-transducing mechanisms in sensors based on 2D TMD nanosheets and their composites are thoroughly discussed. Our aim is to demonstrate a complete concept in this rapidly emerging research area and to address basic knowledge, opportunities, and challenges in this promising field. We expect that more 2D TMD nanosheets and their composites, as well as more sensing strategies, will be explored in this research field, enabling the fabrication of more accurate sensing devices for practical applications. TMD Nanosheets and Their Composite-Based Electrochemical SensorsThe electrochemical method has been extensively recognized as a powerful tool for fast access to biochemical information in complex samples due to its easy operation, fast response, high sensitivity, and low cost. Inspired by the use of graphene as transducers in electrochemical sensors, [41][42][43] researchers have attempted to use 2D TMD nanosheets as a transducer layer. Their good conductivity, large surface area, fast electron transfer kinetics, high signal/noise ratio, and, more importantly, their feasibility for forming composites, make 2D TMD nanosheets attractive as for electrochemical sensors. [44][45][46][47][48][49][50] Table 1 summarizes the recent progress of electrochemical sensors based on 2D TMD nanosheets and their composites. TMD Nanosheets as a Transducer Layer in Electrochemical SensorsIn 2012, our group developed a single-layer TMD-nanosheetbased electrochemical sensor, in which a single-layer MoS 2nanosheet-modified glassy carbon electrode was directly used for selective detection of dopamine in the presence of uric acid Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets, such as MoS 2 , WS 2 , etc., are attracting increasing interest due to their intriguing physical, chemical, electronic, and optical properties. Success in development of methods for large-scale production of 2D TMD nanosheets and their composites has given great potential for various novel applications. In this review, recent progress in sensing applications of 2D TMD nanosheets and their composites is introduced. Moreover, different sensing strategies and signal-transducing mechanisms for sensing devices based on 2D TMD nanosheets and their composites are also summarized and discussed.

Biosensors are powerful tools used to monitor biological and biochemical processes, ranging from clinical diagnosis to disease therapy. The huge demands for bioassays greatly promote the development of new nanomaterials as sensing platforms. Two-dimensional (2D) nanomaterials with superior properties, such as large surface areas and excellent conductivities, are excellent candidates for biosensor applications. Among them, single-or few-layered transition metal dichalcogenide (TMD) nanomaterials represent an emerging class of 2D nanomaterials with unique physical, chemical, and electronic properties. In this mini-review, we summarize the recent progress in 2D TMD nanomaterial-based biosensors for the sensitive detection of various kinds of targets, including nucleic acid, proteins, and small biomolecules, based on different sensors like optical sensors and electrochemical sensors, and bioelectronic sensors. Finally, the challenges and opportunities in this promising field are also proposed.

Carbon-based functional materials hold the key for solving global challenges in the areas of water scarcity and the energy crisis. Although carbon nanotubes (CNTs) and graphene have shown promising results in various fields of application, their high preparation cost and low production yield still dramatically hinder their wide practical applications. Therefore, there is an urgent call for preparing carbon-based functional materials from low-cost, abundant, and sustainable sources. Recent innovative strategies have been developed to convert various waste materials into valuable carbon-based functional materials. These waste-derived carbon-based functional materials have shown great potential in many applications, especially as sorbents for water remediation and electrodes for energy storage. Here, the research progress in the preparation of waste-derived carbon-based functional materials is summarized, along with their applications in water remediation and energy storage; challenges and future research directions in this emerging research field are also discussed.