Two-dimensional dielectric nanosheets: novel nanoelectronics from nanocrystal building blocks

Two-dimensional (2D) nanosheets, which possess atomic or molecular thickness and infinite planar lengths, are regarded as the thinnest functional nanomaterials. The recent development of methods for manipulating graphene (carbon nanosheet) has provided new possibilities and applications for 2D systems; many amazing functionalities such as high electron mobility and quantum Hall effects have been discovered. However, graphene is a conductor, and electronic technology also requires insulators, which are essential for many devices such as memories, capacitors, and gate dielectrics. Along with graphene, inorganic nanosheets have thus increasingly attracted fundamental research interest because they have the potential to be used as dielectric alternatives in next-generation nanoelectronics. Here, we review the progress made in the properties of dielectric nanosheets, highlighting emerging functionalities in electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanoelectronics.     

Formation of chiral branched nanowires by the Eshelby Twist

Manipulating the morphology of inorganic nanostructures, such as their chirality and branching structure, has been actively pursued as a means of controlling their electrical, optical and mechanical properties. Notable examples of chiral inorganic nanostructures include carbon nanotubes, gold multishell nanowires, mesoporous nanowires and helical nanowires. Branched nanostructures have also been studied and been shown to have interesting properties for energy harvesting and nanoelectronics. Combining both chiral and branching motifs into nanostructures might provide new materials properties. Here we show a chiral branched PbSe nanowire structure, which is formed by a vapour-liquid-solid branching from a central nanowire with an axial screw dislocation. The chirality is caused by the elastic strain of the axial screw dislocation, which produces a corresponding Eshelby Twist in the nanowires. In addition to opening up new opportunities for tailoring the properties of nanomaterials, these chiral branched nanowires also provide a direct visualization of the Eshelby Twist.     

石墨及其改性产物研究进展

天然石墨是具有片层结构的含碳无机材料,层间由范德华力连接,可用物理或化学方法将其它分子、原子、离子甚至原子团插入其层间,生成石墨层间化合物(GIC);GIC经高温膨胀可得到体积为其几百倍的膨胀石墨(EG);在超声粉碎时,膨胀石墨上的石墨微片剥离,得到纳米石墨微片(NanoG)。近年来,富勒烯(Fullerence)、碳纳米管(CNT)、石墨烯(Graphene)的先后开发,为石墨家族注入新的活力,并为其应用开辟了新的空间。系统论述了天然石墨及其改性产物如EG、NanoG、Graphene、CNT、Fullerence的结构、制备方法、性质及用途。     

Metal Ion-induced Gelation of High-concentration Graphite-like Crystalline Nanosheet Aqueous Suspensions

The stability and transformation of nanomaterial aqueous suspensions are essential for their applications. Preparation of high-concentration carbon nanomaterials suspensions remains challenging due to their nonpolar nature. Herein, 200 mg mL⁻¹ carbon nanomaterial aqueous suspensions are achieved by using graphite-like crystalline nanosheets (GCNs) with high hydrophilicity. Furthermore, these high-concentration GCN aqueous suspensions spontaneously transform into gels when induced by mono-, di-, and trivalent metal salt electrolytes at room temperature. Theoretical calculation of potential energy by DLVO theory reveals that the gelatinized GCNs is a new and metastable state between two usual forms of solution and coagulation. It is shown that the gelation of GCNs is due to the preferential orientation of nanosheets in an edge-edge arrangement, which differs from the case of solution and coagulation. High-temperature treatment of GCN gels produces metal/carbon materials with pore structures. This work provides a promising opportunity to create various metal/carbon functional materials.     

Cationic Copolymer‐Chaperoned 2D–3D Reversible Conversion of Lipid Membranes

Nanosheets have thicknesses on the order of nanometers and planar dimensions in the micrometer range. Nanomaterials that are capable of converting reversibly between 2D nanosheets and 3D structures in response to specific triggers can enable construction of nanodevices. Supra‐molecular lipid nanosheets and their triggered conversions to 3D structures including vesicles and cups are reported. They are produced from lipid vesicles upon addition of amphiphilic peptides and cationic copolymers that act as peptide chaperones. By regulation of the chaperoning activity of the copolymer, 2D to 3D conversions are reversibly triggered, allowing tuning of lipid bilayer structures and functionalities.     

Sustainable and Scalable Synthesis of 2D Ultrathin Hierarchical Porous Carbon Nanosheets for High-Performance Supercapacitor

2D carbon nanomaterials such as graphene, carbon nanosheets, and their derivatives, representing the emerging class of advanced multifunctional materials, have gained great research interest because of their extensive applications ranging from electrochemistry to catalysis. However, sustainable and scalable synthesis of 2D carbon nanosheets (CNs) with hierarchical architecture and irregular structure via a green and low-cost strategy remains a great challenge. Herein, prehydrolysis liquor (PHL), an industrial byproduct of the pulping industry, is first employed to synthesize CNs via a simple hydrothermal carbonization technique. After mild activation with NH₄Cl and FeCl₃, the as-prepared activated CNs (A-CN@NFe) display an ultrathin structure (≈3 nm) and a desirable specific surface area (1021 m² g⁻¹) with hierarchical porous structure, which enables it to be both electroactive materials and structural support materials in nanofibrillated cellulose/A-CN@NFe/polypyrrole (NCP) nanocomposite, and thus endowing nanocomposite with impressive capacitance properties of 2546.3 mF cm⁻² at 1 mA cm⁻². Furthermore, the resultant all-solid-state symmetric supercapacitor delivers a satisfactory energy storage ability of 90.1 µWh cm⁻² at 250.0 µW cm⁻². Thus, this work not only opens a new window for sustainable and scalable synthesis of CNs, but also offers a double profits strategy for energy storage and biorefinery industry.     

复印墨粉色素炭黑的研究

研究了以中色素炉法炭黑（MCF）为基料采用臭氧化制备复印墨粉专用C386色素炭黑的原料配方设计、工艺条件、结构特征和性能，经小试、放大试验和中试生产、工艺稳定，产品性能优良。采用元素分析、红外光谱、Zeta电势和透射电镜表征MCF、C386及进口炭黑，结果表明：MCF经臭氧氧化后，所得C386的羟基（酚羟基）、羰基（醌基）、羧基等官能团增加了，其微观结构和技术性能与迪高沙、卡搏特、三菱炭黑的基本相同。说明该工艺条件对炉法炭黑进行臭氧氧化制备C386的切实可行的。C386用于复配复印墨粉，质量符合要求，用户满意，具有实际应用价值。     

Crab Chitin‐Based 2D Soft Nanomaterials for Fully Biobased Electric Devices

2D nanomaterials have various size/morphology‐dependent properties applicable in electronics, optics, sensing, and actuating. However, intensively studied inorganic 2D nanomaterials are frequently hindered to apply in some particular and industrial fields, owing to harsh synthesis, high‐cost, cytotoxicity, and nondegradability. Endeavor has been made to search for biobased 2D nanomaterials with biocompatibility, sustainability, and biodegradability. A method of hydrophobization‐induced interfacial‐assembly is reported to produce an unprecedented type of nanosheets from marine chitin. During this process, two layers of chitin aggregations assemble into nanosheets with high aspect ratio. With super stability and amphiphilicity, these nanosheets have super ability in creating highly stable Pickering emulsions with internal phase up to 83.4% and droplet size up to 140 μm, in analogue to graphene oxide. Combining emulsifying and carbonization can further convert these 2D precursors to carbon nanosheets with thickness as low as ≈3.8 nm. Having biologic origin, conductivity, and dispersibility in various solvents, resultant carbon nanosheets start a new scenario of exploiting marine resources for fully biobased electric devices with sustainability and biodegradability, e.g., supercapacitor, flexible circuits, and electronic sensors. Hybrid films of chitin and carbon nanosheets also offer low‐cost and environment‐friendly alternative of conductive components desirable in green electronics, wearable electronics, biodegradable circuits, and biologic devices.     

Colloidally Stable Monolayer Nanosheets with Colorimetric Responses

Despite the discovery of chromogenic‐layered materials for decades of years, fabrication of colloidally stable monolayer organic 2D nanosheets in aqueous media with colorimetric responses is still challenging. Herein reported is the first solution synthesis of chromic monolayer nanosheets via the topochemical polymerization of self‐assembled amphiphilic diacetylenes in aqueous media. The polydiacetylene (PDA) nanosheets are ≈3–4 nm thick in solution and only ≈1.9 nm thick in the dried state, while the lateral size can reach several micrometers. Moreover, the aqueous stability endows PDA nanosheets with excellent processability, which can further assemble into films via vacuum filtration or act as an ink for high‐resolution inkjet printing. The filtrated films and printed patterns exhibit fully reversible blue‐to‐red thermochromism, and the film also displays an interesting reversible colorimetric transition in response to near‐infrared light, which is not reported for other PDA‐only systems. The present colloidal PDA nanosheets should represent a new kind of chromic organic 2D nanomaterials that may be applied as novel building blocks for developing intelligent hybrid materials and may also find diverse sensing, display and/or anticounterfeiting applications.     

Pressure vessel problem for chiral elastic tubes

The study of chiral materials is important for the investigation of carbon nanotubes, auxetic materials and bones. The chiral effects cannot be described within classical elasticity. In this paper, the problem of the circular tube under internal and external pressure is solved in the context of the linear theory of chiral Cosserat elasticity. The work is motivated by the recent interest in the using Cosserat elastic solid as model for auxetic materials, bones and chiral carbon nanotubes. First, the generalized plane strain of an isotropic chiral elastic material is investigated. Then, the solution of the pressure vessel problem is established. The salient feature of the solution is that, in the absence of body and surface moments, a pressure acting on the surface of a chiral tube produces a microrotation of the material particles. It is shown that the radial displacement and the radial stress are modified from the values predicted by the theory of achiral materials.     

Fast Gelation of Ti3C2Tx MXene Initiated by Metal Ions

Gelation is an effective way to realize the self‐assembly of nanomaterials into different macrostructures, and in a typical use, the gelation of graphene oxide (GO) produces various graphene‐based carbon materials with different applications. However, the gelation of MXenes, another important type of 2D materials that have different surface chemistry from GO, is difficult to achieve. Here, the first gelation of MXenes in an aqueous dispersion that is initiated by divalent metal ions is reported, where the strong interaction between these ions and ? OH groups on the MXene surface plays a key role. Typically, Fe²⁺ ions are introduced in the MXene dispersion which destroys the electrostatic repulsion force between the MXene nanosheets in the dispersion and acts as linkers to bond the nanosheets together, forming a 3D MXene network. The obtained hydrogel effectively avoids the restacking of the MXene nanosheets and greatly improves their surface utilization, resulting in a high rate performance when used as a supercapacitor electrode (≈226 F g^?1 at 1 V s^?1). It is believed that the gelation of MXenes indicates a new way to build various tunable MXene‐based structures and develop different applications.     

Self‐Assembly of Transition Metal Oxide Nanostructures on MXene Nanosheets for Fast and Stable Lithium Storage

Recently, a new class of 2D materials, i.e., transition metal carbides, nitrides, and carbonitrides known as MXenes, is unveiled with more than 20 types reported one after another. Since they are flexible and conductive, MXenes are expected to compete with graphene and other 2D materials in many applications. Here, a general route is reported to simple self‐assembly of transition metal oxide (TMO) nanostructures, including TiO₂ nanorods and SnO₂ nanowires, on MXene (Ti₃C₂) nanosheets through van der Waals interactions. The MXene nanosheets, acting as the underlying substrate, not only enable reversible electron and ion transport at the interface but also prevent the TMO nanostructures from aggregation during lithiation/delithiation. The TMO nanostructures, in turn, serve as the spacer to prevent the MXene nanosheets from restacking, thus preserving the active areas from being lost. More importantly, they can contribute extraordinary electrochemical properties, offering short lithium diffusion pathways and additional active sites. The resulting TiO₂/MXene and SnO₂/MXene heterostructures exhibit superior high‐rate performance, making them promising high‐power and high‐energy anode materials for lithium‐ion batteries.     

Circularly Polarized Luminescence in Nanoassemblies: Generation,Amplification, and Application

Currently, the development of circularly polarized luminescent (CPL) materials has drawn extensive attention due to the numerous potential applications in optical data storage, displays, backlights in 3D displays, and so on. While the fabrication of CPL-active materials generally requires chiral luminescent molecules, the introduction of the “self-assembly” concept offers a new perspective in obtaining the CPL-active materials. Following this approach, various self-assembled materials, including organic-, inorganic-, and hybrid systems can be endowed with CPL properties. Benefiting from the advantages of self-assembly, not only chiral molecules, but also achiral species, as well as inorganic nanoparticles have potential to be self-assembled into chiral nanoassemblies showing CPL activity. In addition, the dissymmetry factor, an important parameter of CPL materials, can be enhanced through various pathways of self-assembly. Here, the present status and progress of self-assembled nanomaterials with CPL activity are reviewed. An overview of the key factors in regulating chiral emission materials at the supramolecular level will largely boost their application in multidisciplinary fields.     

Chemical and Colloidal Dynamics of MnO2 Nanosheets in Biological Media Relevant for Nanosafety Assessment

Many layered crystal phases can be exfoliated or assembled into ultrathin 2D nanosheets with novel properties not achievable by particulate or fibrous nanoforms. Among these 2D materials are manganese dioxide (MnO₂) nanosheets, which have applications in batteries, catalysts, and biomedical probes. A novel feature of MnO₂ is its sensitivity to chemical reduction leading to dissolution and Mn²⁺ release. Biodissolution is critical for nanosafety assessment of 2D materials, but the timing and location of MnO₂ biodissolution in environmental or occupational exposure scenarios are poorly understood. This work investigates the chemical and colloidal dynamics of MnO₂ nanosheets in biological media for environmental and human health risk assessment. MnO₂ nanosheets are insoluble in most aqueous phases, but react with strong and weak reducing agents in biological fluid environments. In vitro, reductive dissolution can be slow enough in cell culture media for MnO₂ internalization by cells in the form of intact nanosheets, which localize in vacuoles, react to deplete intracellular glutathione, and induce cytotoxicity that is likely mediated by intracellular Mn²⁺ release. The results are used to classify MnO₂ nanosheets within a new hazard screening framework for 2D materials, and the implications of MnO₂ transformations for nanotoxicity testing and nanosafety assessment are discussed.     

Van der Waals Epitaxial Growth of 2D Metallic Vanadium Diselenide Single Crystals and their Extra‐High Electrical Conductivity

2D metallic transition‐metal dichalcogenides (MTMDs) have recently emerged as a new class of materials for the engineering of novel electronic phases, 2D superconductors, magnets, as well as novel electronic applications. However, the mechanical exfoliation route is predominantly used to obtain such metallic 2D flakes, but the batch production remains challenging. Herein, the van der Waals epitaxial growth of monocrystalline, 1T‐phase, few‐layer metallic VSe₂ nanosheets on an atomically flat mica substrate via a “one‐step” chemical vapor deposition method is reported. The thickness of the VSe₂ nanosheets is precisely tuned from several nanometers to several tenths of nanometers. More significantly, the 2D VSe₂ single crystals are found to present an excellent metallic feature, as evidenced by the extra‐high electrical conductivity of up to 10⁶ S m^?1, 1–4 orders of magnitude higher than that of various conductive 2D materials. The thickness‐dependent charge‐density‐wave phase transitions are also examined through low‐temperature transport measurements, which reveal that the synthesized 2D metallic 1T‐VSe₂ nanosheets should serve as good research platforms for the detecting novel many‐body states. These results open a new path for the synthesis and property investigations of nanoscale‐thickness 2D MTMDs crystals.     

Effect of different structures on the gas sensing property of ZnO

We have successfully reported a new diamond-like morphology of zinc oxide (ZnO) structures via a simple hydrothermal method and discussed its probable growth mechanism. Compared with other morphologies of ZnO structures (microrods and nanosheets), nanodiamonds have excellent gas-sensing property owning to its large specific surface area, holding the perfect promise for ZnO powders as underlying gas-sensing materials. Furthermore, the as-prepared nanosheets assisted with the sodium citrate as an additive were found to show better gas-sensing property due to the smaller size than microrods. We found the positive role of the sodium citrate and reaction time in the growth of nanosheets and nanodiamonds respectively and the corresponding influences on growth mechanism were discussed.     

NaCl-template assisted preparation of porous carbon nanosheets started from lignin for efficient removal of tetracycline

We report here the preparation of lignin-based porous carbon nanosheets (LPCNS) using renewable lignin as a precursor and NaCl as a green template via a KOH activation for removing tetracycline (TC). Different techniques were employed to analyze the physicochemical properties of LPCNS. The LPCNS possessed high specific surface area of 3505?m² g^?1 and large pore volume of 2.0?cm³ g^?1. Moreover, the batch adsorption tests using LPCNS showed that the equilibrium adsorption amount was 1613?mg?g^?1 for TC at 298?K. Additionally, the LPCNS exhibited fast kinetics performance and good regeneration performance. This advanced carbon adsorbent with nanosheet structure showed enhanced adsorption performance compared to bulk carbon. This environment-friendly and low-cost salt-template strategy for the fabrication of carbon nanosheets hold promise to design biomass-based carbon nanosheets or even other sheet materials.     

Fabrication of high-pore volume carbon nanosheets with uniform arrangement of mesopores

Carbon nanosheets with a tunable mesopore size,large pore volume,and good electronic conductivity are synthesized via a solution-chemistry approach.In this synthesis,diaminohexane and graphene oxide (GO) are used as the structural directing agents,and a silica colloid is used as a mesopores template.Diaminohexane plays a crucial role in bridging silica colloid particles and GO,as well as initiating the polymerization of benzoxazine on the surfaces of both the GO and silica,resulting in the formation of a hybrid nanosheet polymer.The carbon nanosheets have graphene embedded in them and have several spherical mesopores with a pore volume up to 3.5 cm3·g-1 on their surfaces.These nuerous accessible mesopores in the carbon layers can act as reservoirs to host a high loading of active charge-storage materials with good dispersion and a uniform particle size.Compared with active materials with wide particle-size distributions,the unique proposed configuration with confined and uniform particles exhibits superior electrochemical performance during lithiation and delithiation,especially during long cycles and at high rates.     

A Universal Strategy for Intimately Coupled Carbon Nanosheets/MoM Nanocrystals (M = P,S, C,and O) Hierarchical Hollow Nanospheres for Hydrogen Evolution Catalysis and Sodium‐Ion Storage

Intimately coupled carbon/transition‐metal‐based hierarchical nanostructures are one of most interesting electrode materials for boosting energy conversion and storage applications owing to the strong synergistic effect between the two components and appealing structural stability. Herein, a universal method is reported for making hierarchical hollow carbon nanospheres (HCSs) with intimately coupled ultrathin carbon nanosheets and Mo‐based nanocrystals. The in situ and confined reaction of the synthetic strategy can not only allow the aggregation of the nanocrystals to be impeded, but also endows extremely intimate coupled interaction between the conductive carbon nanosheets and the nanocrystals MoM (M = P, S, C and O). As a proof of concept, the as‐prepared MoP/C HCSs exhibit extraordinary hydrogen evolution reaction electrocatalytic activity with small overpotential and robust durability in both acidic and alkaline solutions. In addition, the unique sheet‐on‐sheet MoS₂/C HCSs as an anode demonstrate high capacity, great rate capabilities, and long‐term cycles for sodium‐ion batteries (SIBs). The capacity can be maintained at 410 mA h g^?1 even after 1000 cycles even at a high current density of 4 A g^?1, one of the best reported values for MoS₂‐based electrode materials for SIBs. The present work highlights the importance of designing and fabricating functional strongly coupled hybrid materials for enhancing energy conversion and storage applications.     

2D Porous Carbons prepared from Layered Organic–Inorganic Hybrids and their Use as Oxygen‐Reduction Electrocatalysts

2D porous carbon nanomaterials have attracted tremendous attention in different disciplines especially for electrochemical catalysis. The significant advantage of such 2D materials is that nearly all their surfaces are exposed to the electrolyte and can take part in the electrochemical reaction. Here, a versatile active‐salt‐templating strategy to efficiently synthesize 2D porous carbon nanosheets from layered organic–inorganic hybrids is presented. The resulting heteroatom‐doped carbon nanosheets (NFe/CNs) exhibit exceptional performance for the oxygen‐reduction reaction and in Zn–air battery electrodes. The activity of the best catalyst within a series of NFe/CNs exceeds the performance of conventional carbon‐supported Pt catalysts in terms of onset potential (0.930 vs 0.915 V of Pt/C), half‐wave potential (0.859 vs 0.816 V of Pt/C), long‐time stability, and methanol tolerance. Also, when applied as a cathode catalyst in a zinc–air battery the NFe/CNs presented here outperform commercial Pt/C catalysts.