Controlled Gas Exfoliation of Boron Nitride into Few‐Layered Nanosheets

The controlled exfoliation of hexagonal boron nitride (h‐BN) into single‐ or few‐layered nanosheets remains a grand challenge and becomes the bottleneck to essential studies and applications of h‐BN. Here, we present an efficient strategy for the scalable synthesis of few‐layered h‐BN nanosheets (BNNS) using a novel gas exfoliation of bulk h‐BN in liquid N₂ (L‐N₂). The essence of this strategy lies in the combination of a high temperature triggered expansion of bulk h‐BN and the cryogenic L ‐N₂ gasification to exfoliate the h‐BN. The produced BNNS after ten cycles (BNNS‐10) consisted primarily of fewer than five atomic layers with a high mass yield of 16–20 %. N₂ sorption and desorption isotherms show that the BNNS‐10 exhibited a much higher specific surface area of 278 m² g^?1 than that of bulk BN (10 m² g^?1). Through the investigation of the exfoliated intermediates combined with a theoretical calculation, we found that the huge temperature variation initiates the expansion and curling of the bulk h‐BN. Subseqently, the L ‐N₂ penetrates into the interlayers of h‐BN along the curling edge, followed by an immediate drastic gasification of L ‐N₂, further peeling off h‐BN. This novel gas exfoliation of high surface area BNNS not only opens up potential opportunities for wide applications, but also can be extended to produce other layered materials in high yields.     

Heteroatom‐Doped Porous Carbon Nanosheets: General Preparation and Enhanced Capacitive Properties

High‐performance electrical double‐layer capacitors (EDLCs) require carbon electrode materials with high specific surface area, short ion‐diffusion pathways, and outstanding electrical conductivity. Herein, a general approach combing the molten‐salt method and chemical activation to prepare N‐doped carbon nanosheets with high surface area (654 m² g^?1) and adjustable porous structure is presented. Owing to their structural features, the N‐doped carbon nanosheets exhibited superior capacitive performance, demonstrated by a maximum capacitance of 243 F g^?1 (area‐normalized capacitance up to 37 μF cm^?2) at a current density of 0.5 A g^?1 in aqueous electrolyte, high rate capability (179 F g^?1 at 20 A g^?1), and excellent cycle stability. This method provides a new route to prepare porous and heteroatom‐doped carbon nanosheets for high‐performance EDLCs, which could also be extended to other polymer precursors and even waste biomass.     

Controllable Synthesis of Few‐Layer Bismuth Subcarbonate by Electrochemical Exfoliation for Enhanced CO2 Reduction Performance

Two‐dimensional (2D) engineering of materials has been recently explored to enhance the performance of electrocatalysts by reducing their dimensionality and introducing more catalytically active ones. In this work, controllable synthesis of few‐layer bismuth subcarbonate nanosheets has been achieved via an electrochemical exfoliation method. These nanosheets catalyse CO₂ reduction to formate with high faradaic efficiency and high current density at a low overpotential owing to the 2D structure and co‐existence of bismuth subcarbonate and bismuth metal under catalytic turnover conditions. Two underlying fast electron transfer processes revealed by Fourier‐transformed alternating current voltammetry (FTacV) are attributed to CO₂ reduction at bismuth subcarbonate and bismuth metal. FTacV results also suggest that protonation of CO₂^.? is the rate determining step for bismuth catalysed CO₂ reduction.     

Few‐Layer Antimonene by Liquid‐Phase Exfoliation

We report on a fast and simple method to produce highly stable isopropanol/water (4:1) suspensions of few‐layer antimonene by liquid‐phase exfoliation of antimony crystals in a process that is assisted by sonication but does not require the addition of any surfactant. This straightforward method generates dispersions of few‐layer antimonene suitable for on‐surface isolation. Analysis by atomic force microscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy confirmed the formation of high‐quality few‐layer antimonene nanosheets with large lateral dimensions. These nanolayers are extremely stable under ambient conditions. Their Raman signals are strongly thickness‐dependent, which was rationalized by means of density functional theory calculations.     

Solution‐Phase Synthesis of Few‐Layer Hexagonal Antimonene Nanosheets via Anisotropic Growth

Antimonene, an emerging two‐dimensional material, has garnered tremendous interest due to its intriguing structure and fascinating electronic properties. However, the synthesis of high‐quality few‐layer antimonene nanosheets, which can only be produced by exfoliation or epitaxial growth on exotic substrates, has greatly hindered the development of this new field. Herein, few‐layer hexagonal and functionalized antimonene nanosheets were successfully prepared from SbCl₃ solutions for the first time by exclusively promoting their anisotropic growth in a colloidal solution. Oleylamine was selected as the reducing agent, rather than oleic acid, and dodecylthiol was key to preventing the formation of antimony oxide. Additionally, halide ions adsorbed on the surface also influenced the anisotropic growth of hexagonal antimonene nanosheets. Atomic force microscopy (AFM) revealed that the sheets were ≈5 nm thick; Raman spectroscopy and X‐ray diffraction (XRD) revealed a rhombohedral atomic structure (β‐Sb) with excellent stability.     

Unlocking the Electrocatalytic Activity of Antimony for CO2 Reduction by Two‐Dimensional Engineering of the Bulk Material

Two‐dimensional (2D) materials are known to be useful in catalysis. Engineering 3D bulk materials into the 2D form can enhance the exposure of the active edge sites, which are believed to be the origin of the high catalytic activity. Reported herein is the production of 2D “few‐layer” antimony (Sb) nanosheets by cathodic exfoliation. Application of this 2D engineering method turns Sb, an inactive material for CO₂ reduction in its bulk form, into an active 2D electrocatalyst for reduction of CO₂ to formate with high efficiency. The high activity is attributed to the exposure of a large number of catalytically active edge sites. Moreover, this cathodic exfoliation process can be coupled with the anodic exfoliation of graphite in a single‐compartment cell for in situ production of a few‐layer Sb nanosheets and graphene composite. The observed increased activity of this composite is attributed to the strong electronic interaction between graphene and Sb.     

Iridium‐Catalyst‐Based Autonomous Bubble‐Propelled Graphene Micromotors with Ultralow Catalyst Loading

A novel concept of an iridium‐based bubble‐propelled Janus‐particle‐type graphene micromotor with very high surface area and with very low catalyst loading is described. The low loading of Ir catalyst (0.54 at %) allows for fast motion of graphene microparticles with high surface area of 316.2 m² g^?1. The micromotor was prepared with a simple and scalable method by thermal exfoliation of iridium‐doped graphite oxide precursor composite in hydrogen atmosphere. Oxygen bubbles generated from the decomposition of hydrogen peroxide at the iridium catalytic sites provide robust propulsion thrust for the graphene micromotor. The high surface area and low iridium catalyst loading of the bubble‐propelled graphene motors offer great possibilities for dramatically enhanced cargo delivery.     

Electrochemical Exfoliation of Pillared‐Layer Metal–Organic Framework to Boost the Oxygen Evolution Reaction

Two‐dimensional (2D) materials and ultrathin nanosheets are advantageous for elevating the catalysis performance and elucidating the catalysis mechanism of heterogeneous catalysts, but they are mostly restricted to inorganic or organic materials based on covalent bonds. We report an electrochemical/chemical exfoliation strategy for synthesizing metal–organic 2D materials based on coordination bonds. A catechol functionalized ligand is used as the redox active pillar to construct a pillared‐layer framework. When the 3D pillared‐layer MOF serves as an electrocatalyst for water oxidation (pH 13), the pillar ligands can be oxidized in situ and removed. The remaining ultrathin (2 nm) nanosheets of the metal–organic layers are an efficient catalyst with overpotentials as low as 211 mV at 10 mA cm^?2 and a turnover frequency as high as 30 s^?1 at an overpotential of 300 mV.     

Highly Efficient,Green, and Scalable β‐Cyclodextrin‐Assisted Aqueous Exfoliation of Transition‐Metal Dichalcogenides: MoS2 and ReS2 Nanoflakes

The β‐cyclodextrin‐assisted aqueous‐exfoliation method was used to prepare transition‐metal dichalcogenide (TMD) nanosheets, in a cheap, highly efficient, scalable and environmentally friendly manner. As study cases, MoS₂ and ReS₂ nanoflakes were prepared according to this method. Particularly, the effective exfoliation of ReS₂ crystals in an aqueous environment was observed for the first time. Moreover, exfoliated nanomaterials can be readily utilized in hydrogen evolution reactions (HERs) as noble‐metal‐free catalysts. This work provides new opportunities for highly efficient exfoliation of TMDs and other 2D nanomaterials into few‐layer nanosheets in aqueous media. Their production process showed high biocompatibility, broad applicability and excellent sustainability.     

Preparation of the Monolith of Hierarchical Macro‐/Mesoporous Calcium Silicate Ultrathin Nanosheets with Low Thermal Conductivity by Means of Ambient‐Pressure Drying

Calcium silicate monolith was prepared by the hydrothermal reaction of a slurry of SiO₂, calcium hydroxide, and surfactant (OP‐10) obtained by high‐energy ball milling, followed by drying at ambient pressure. By using this strategy, the shrinkage due to the collapse of pores during the drying of porous materials, which is a commonly observed phenomena, was successfully avoided. It has a unique microstructure of hierarchical macro‐/mesoporous ultrathin calcium silicate nanosheets with a layered gyrolite crystalline structure. Very interestingly, the calcium silicate nanosheets can be peeled off to give a single‐layer nanosheet (1.23 nm) of gyrolite by ultrasonication. The monolith has a low apparent density (0.073 g cm^?3) and low thermal conductivity (0.0399 W K^?1 m^?1). The reasons behind why the formation of the unique hierarchical macro‐/mesoporous ultrathin nanosheets avoids shrinkage during the hydrothermal reaction and drying, and considerably decreases the thermal conductivity, is discussed.     

Few‐Layer Borocarbonitride Nanosheets: Platinum‐Free Catalyst for the Oxygen Reduction Reaction

The present study demonstrates the use of few‐layer borocarbonitride nanosheets synthesized by a simple method as non‐platinum cathode catalysts for the oxygen reduction reaction (ORR) in alkaline medium. Composition‐dependent ORR activity is observed and the best performance was found when the composition was carbon‐rich. Mechanistic aspects reveal that ORR follows the 4 e^? pathway with kinetic parameters comparable to those of the commercial Pt/C catalyst. Excellent methanol tolerance is observed with the BCN nanosheets unlike with Pt/C.     

Synthesis of Two‐dimensional Microporous Carbonaceous Polymer Nanosheets and Their Application as High‐performance CO2 Capture Sorbent

The synthesis of two‐dimensional (2D) polymer nanosheets with a well‐defined microporous structure remains challenging in materials science. Here, a new kind of 2D microporous carbonaceous polymer nanosheets was synthesized through polymerization of a very low concentration of 1,4‐dicyanobenzene in molten zinc chloride at 400–500 °C. This type of nanosheets has a thickness in the range of 3–20 nm, well‐defined microporosity, a high surface area (～537 m² g^?1), and a large micropore volume (～0.45 cm³ g^?1). The microporous carbonaceous polymer nanosheets exhibit superior CO₂ sorption capability (8.14 wt % at 298 K and 1 bar) and a relatively high CO₂ selectivity toward N₂ (25.6). Starting from different aromatic nitrile monomers, a variety of 2D carbonaceous polymer nanosheets can be obtained showing a certain universality of the ionothermal method reported herein.     

Visible‐Light‐Induced Generation of H2 by Nanocomposites of Few‐Layer TiS2 and TaS2 with CdS Nanoparticles

Graphene analogues of TaS₂ and TiS₂ (3–4 layers), prepared by Li intercalation followed by exfoliation in water, were characterized. Nanocomposites of CdS with few‐layer TiS₂ and TaS₂ were employed for the visible‐light‐induced H₂ evolution reaction (HER). Benzyl alcohol was used as the sacrificial electron donor, which was oxidized to benzaldehyde during the reaction. Few‐layer TiS₂ is a semiconductor with a band gap of 0.7 eV, and its nanocomposite with CdS showed an activity of 1000 μmol h^?1 g^?1_. The nanocomposite of few‐layer TaS₂, in contrast, gave rise to higher activity of 2320 μmol h^?1 g^?1, which was attributed to the metallic nature of few‐layer TaS₂. The amount of hydrogen evolved after 20 and 16 h for the CdS/TiS₂ and CdS/TaS₂ nanocomposites was 14833 and 28132 μmol, respectively, with turnover frequencies of 0.24 and 0.57 h^?1, respectively.     

Generalized Low‐Temperature Fabrication of Scalable Multi‐Type Two‐Dimensional Nanosheets with a Green Soft Template

Two‐dimensional nanosheets with high specific surface areas and fascinating physical and chemical properties have attracted tremendous interests because of their promising potentials in both fundamental research and practical applications. However, the problem of developing a universal strategy with a facile and cost‐effective synthesis process for multi‐type ultrathin 2 D nanostructures remains unresolved. Herein, we report a generalized low‐temperature fabrication of scalable multi‐type 2 D nanosheets including metal hydroxides (such as Ni(OH)₂, Co(OH)₂, Cd(OH)₂, and Mg(OH)₂), metal oxides (such as ZnO and Mn₃O₄), and layered mixed transition‐metal hydroxides (Ni‐Co LDH, Ni‐Fe LDH, Co‐Fe LDH, and Ni‐Co‐Fe layered ternary hydroxides) through the rational employment of a green soft‐template. The synthesized crystalline inorganic nanosheets possess confined thickness, resulting in ultrahigh surface atom ratios and chemically reactive facets. Upon evaluation as electrode materials for pseudocapacitors, the Ni‐Co LDH nanosheets exhibit a high specific capacitance of 1087 F g^?1 at a current density of 1 A g^?1, and excellent stability, with 103 % retention after 500 cycles. This strategy is facile and scalable for the production of high‐quality ultrathin crystalline inorganic nanosheets, with the possibility of extension to the preparation of other complex nanosheets.     

Two‐Dimensional Metal–Organic Framework Nanosheets for Membrane‐Based Gas Separation

Metal–organic framework (MOF) nanosheets could serve as ideal building blocks of molecular sieve membranes owing to their structural diversity and minimized mass‐transfer barrier. To date, discovery of appropriate MOF nanosheets and facile fabrication of high performance MOF nanosheet‐based membranes remain as great challenges. A modified soft‐physical exfoliation method was used to disintegrate a lamellar amphiprotic MOF into nanosheets with a high aspect ratio. Consequently sub‐10 nm‐thick ultrathin membranes were successfully prepared, and these demonstrated a remarkable H₂/CO₂ separation performance, with a separation factor of up to 166 and H₂ permeance of up to 8×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at elevated testing temperatures owing to a well‐defined size‐exclusion effect. This nanosheet‐based membrane holds great promise as the next generation of ultrapermeable gas separation membrane.     

Surface modification of polyester by oxygen‐ and nitrogen‐plasma treatment

In this paper, we present a study on the surface modification of polyethyleneterephthalate (PET) polymer by plasma treatment. The samples were treated by nitrogen and oxygen plasma for different time periods between 3 and 90 s. The plasma was created by a radio frequency (RF) generator. The gas pressure was fixed at 75 Pa and the discharge power was set to 200 W. The samples were treated in the glow region, where the electrons temperature was about 4 eV, the positive ions density was about 2 × 10¹⁵ m^?3, and the neutral atom density was about 4 × 10²¹ m^?3 for oxygen and 1 × 10²¹ m^?3 for nitrogen. The changes in surface morphology were observed by using atomic force microscopy (AFM). Surface wettability was determined by water contact angle measurements while the chemical composition of the surface was analyzed using XPS. The stability of functional groups on the polymer surface treated with plasma was monitored by XPS and wettability measurements in different time intervals. The oxygen‐plasma‐treated samples showed much more pronounced changes in the surface topography compared to those treated by nitrogen plasma. The contact angle of a water drop decreased from 75° for the untreated sample to 20° for oxygen and 25° for nitrogen‐plasma‐treated samples for 3 s. It kept decreasing with treatment time for both plasmas and reached about 10° for nitrogen plasma after 1 min of plasma treatment. For oxygen plasma, however, the contact angle kept decreasing even after a minute of plasma treatment and eventually fell below a few degrees. We found that the water contact angle increased linearly with the O/C ratio or N/C ratio in the case of oxygen or nitrogen plasma, respectively. Ageing effects of the plasma‐treated surface were more pronounced in the first 3 days; however, the surface hydrophilicity was rather stable later. Copyright © 2008 John Wiley & Sons, Ltd.     

Exfoliation of Graphite into Graphene in Polar Solvents Mediated by Amphiphilic Hexa‐peri‐hexabenzocoronene

A water‐soluble surfactant consisting of hexa‐peri‐hexabenzocoronene (HBC) as hydrophobic aromatic core and hydrophilic carboxy substituents was synthesized. It exhibited a self‐assembled nanofiber structure in the solid state. Profiting from the π interactions between the large aromatic core of HBC and graphene, the surfactant mediated the exfoliation of graphite into graphene in polar solvents, which was further stabilized by the bulky hydrophilic carboxylic groups. A graphene dispersion with a concentration as high as 1.1 mg L^?1 containing 2–6 multilayer nanosheets was obtained. The lateral size of the graphene sheets was in the range of 100–500 nm based on atomic force microscope (AFM) and transmission electron microscope (TEM) measurements.     

Two‐Dimensional Cobalt‐/Nickel‐Based Oxide Nanosheets for High‐Performance Sodium and Lithium Storage

Two‐dimensional (2D) nanomaterials are one of the most promising types of candidates for energy‐storage applications due to confined thicknesses and high surface areas, which would play an essential role in enhanced reaction kinetics. Herein, a universal process that can be extended for scale up is developed to synthesise ultrathin cobalt‐/nickel‐based hydroxides and oxides. The sodium and lithium storage capabilities of Co₃O₄ nanosheets are evaluated in detail. For sodium storage, the Co₃O₄ nanosheets exhibit excellent rate capability (e.g., 179 mA h g^?1 at 7.0 A g^?1 and 150 mA h g^?1 at 10.0 A g^?1) and promising cycling performance (404 mA h g^?1 after 100 cycles at 0.1 A g^?1). Meanwhile, very impressive lithium storage performance is also achieved, which is maintained at 1029 mA h g^?1 after 100 cycles at 0.2 A g^?1. NiO and NiCo₂O₄ nanosheets are also successfully prepared through the same synthetic approach, and both deliver very encouraging lithium storage performances. In addition to rechargeable batteries, 2D cobalt‐/nickel‐based hydroxides and oxides are also anticipated to have great potential applications in supercapacitors, electrocatalysis and other energy‐storage‐/‐conversion‐related fields.     

Rational Design of Ni Nanoparticles on N‐Rich Ultrathin Carbon Nanosheets for High‐Performance Supercapacitor Materials: Embedded‐ Versus Anchored‐Type Dispersion

Highly dispersed Ni nanoparticles (NPs) and abundant functional N‐species were integrated into ultrathin carbon nanosheets by using a facile and economical sol–gel route. Embedded‐ and anchored‐type configurations were achieved for the dispersion of Ni NPs in/on N‐rich carbon nanosheets. The anchored‐type composite exhibited outstanding pseudocapacitance of 2200 F g^?1 at 5 A g^?1 with unusual rate capability and extraordinary cyclic stability over 20 000 cycles with little capacitance decay. Aqueous asymmetric supercapacitors fabricated with this composite cathode demonstrated a high energy density of 51.3 Wh kg^?1 at a relatively large power density of 421.6 W kg^?1, along with outstanding cyclic stability. This approach opens an attractive direction for enhancing the electrochemical performances of metal‐based supercapacitors and can be generalized to design high‐performance energy‐storage devices.     

Three‐Dimensional Macroassembly of Sandwich‐Like,Hierarchical, Porous Carbon/Graphene Nanosheets towards Ultralight,Superhigh Surface Area,Multifunctional Aerogels

A new, ultralight, superhigh surface area, multifunctional aerogel, which is macroassembled from sandwich‐like, hierarchical, porous carbon/graphene nanosheets, is described. The multifunctional aerogel was characterized by means of XRD, SEM, TEM, Raman spectroscopy, and UV/Vis absorption spectroscopy. The multifunctional aerogel had an ultralow density of 8 mg cm^?3 and a superhigh surface area of 2650 m² g^?1. The multifunctional aerogel was thermal stability and compressible. Meanwhile, the multifunctional aerogel exhibited high capacity for the adsorption of oils and organic solvents, unexpectedly high hydrogen adsorption and good electrochemical performance.