Fast Exfoliation and Functionalisation of Two‐Dimensional Crystalline Carbon Nitride by Framework Charging

Two‐dimensional (2D) layered graphitic carbon nitride (gCN) nanosheets offer intriguing electronic and chemical properties. However, the exfoliation and functionalisation of gCN for specific applications remain challenging. We report a scalable one‐pot reductive method to produce solutions of single‐ and few‐layer 2D gCN nanosheets with excellent stability in a high mass yield (35 %) from polytriazine imide. High‐resolution imaging confirmed the intact crystalline structure and identified an AB stacking for gCN layers. The charge allows deliberate organic functionalisation of dissolved gCN, providing a general route to adjust their properties.     

Polymeric Carbon Nitride/Reduced Graphene Oxide/Fe2O3: All‐Solid‐State Z‐Scheme System for Photocatalytic Overall Water Splitting

The charge transfer between hydrogen evolution photocatalysts (HEPs) and oxygen evolution photocatalysts (OEPs) is the rate‐determining step that controls the overall performance of a Z‐scheme water‐splitting system. Here, we carefully design reduced graphene oxide (RGO) nanosheets for use as solid‐state mediators to accelerate the charge carrier transfer between HEPs (e.g., polymeric carbon nitride (PCN)) and OEPs (e.g., Fe₂O₃), thus achieving efficient overall water splitting. The important role of RGO could also be further proven in other PCN‐based Z‐systems (BiVO₄/RGO/PCN and WO₃/RGO/PCN), illustrating the universality of this strategy.     

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.     

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.     

Coating Polymeric Carbon Nitride Photoanodes on Conductive Y:ZnO Nanorod Arrays for Overall Water Splitting

Polymeric carbon nitride (PCN) photosensitizers are proposed replacements for their inorganic counterparts in solar‐to‐fuel conversion via photoelectrochemical water splitting. However, intense charge recombination, primarily because of surface defects, limits the use of PCN in PEC systems. Now, photoanodes are designed by coating PCN films onto highly conductive yttrium‐doped zinc oxide (Y:ZnO) nanorods (NRs) serving as charge collectors. The generation of charge carriers can therefore be promoted by this type II alignment. The charge collectors would be kept nearby for charge separation and transport to be used in the interfacial redox reactions. The photocurrent density of the polymer electrode is improved to 0.4 mA cm^?2 at 1.23 V vs. the reversible hydrogen electrode in a Na₂SO₄ electrolyte solution under AM 1.5 illumination. The result reveals a more than 50‐fold enhancement over the PCN films achieved by powder; the efficiency can be preserved at 95 % for 160 minutes.     

Supramolecularly Bonded Layered Heterostructures Exhibiting HER Activity

van der Waals heterostructures formed by 2D materials have attracted much attention in the last few years. Recently, 2D nanosheets linked by covalent bonds have been found to exhibit novel properties. In the present study we have investigated supramolecular layered heterostructures formed by nanosheets of MoS₂ with BC₇N, g‐C₃N₄ and graphene. These materials have been synthesized via a non‐covalent host–guest synthetic design using cucurbit[8]uril (CB[8]) hosts. In addition to offering reversible disassembly, these heterostructures show good visible‐light‐driven hydrogen evolution reaction (HER) activity as well as reasonable gas adsorption and other properties.     

Amino‐Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g‐C3N4 for Enhanced Photocatalytic CO2 Reduction

Halide perovskite quantum dots (QDs) have great potential in photocatalytic applications if their low charge transportation efficiency and chemical instability can be overcome. To circumvent these obstacles, we anchored CsPbBr₃ QDs (CPB) on NH_x‐rich porous g‐C₃N₄ nanosheets (PCN) to construct the composite photocatalysts via N?Br chemical bonding. The 20 CPB‐PCN (20 wt % of QDs) photocatalyst exhibits good stability and an outstanding yield of 149 μmol h^?1 g^?1 in acetonitrile/water for photocatalytic reduction of CO₂ to CO under visible light irradiation, which is around 15 times higher than that of CsPbBr₃ QDs. This study opens up new possibilities of using halide perovskite QDs for photocatalytic application.     

Two‐Dimensional Tellurium Nanosheets Exhibiting an Anomalous Switchable Photoresponse with Thickness Dependence

Two‐dimensional (2D) tellurium (Te) was recently predicted to be promising for diverse electronic and optoelectronic applications. However, the synthesis of high‐quality 2D Te structures remains challenging, which greatly hinders the exploration of its full properties. Herein, an anomalous photoresponse from negative to positive as a function of thickness in Te nanosheets is reported. Ultrathin Te layers with large size and clean interface were obtained through a topotactic transformation, in which the 2D Te structure was derived from a layered MTe₂ (M=Ti, Mo, W) matrix by excessive lithiation. Prominently, the photoresponse in Te nanosheets exhibits negative behavior when the thickness is less than 5 nm, which turns positive as the thickness increases. This unusual photoresponse will shed light on the full exploration of 2D non‐layered materials with exotic properties.     

Facile Synthesis of Ultrathin Lepidocrocite Nanosheets from Layered Precursors

Ultrathin two‐dimensional nanosheets have been widely studied because of their peculiar properties and promising applications. As a typical layered material, successful exfoliation of freestanding ultrathin lepidocrocite (γ‐FeOOH) nanosheets from the bulk material has not been reported to date. Herein, we report a facile synthetic route to prepare ultrathin lepidocrocite nanosheets with a thickness of approximately 2–3 nm from FeO_x–propanediol layered precursors through weakening of the hydrogen bonds during the crystallization process. The ultrathin morphology and single‐crystal structure of the nanosheets were confirmed by transmission electron microscopy, X‐ray diffraction, and atomic force microscopy. The formation process of these nanosheets demonstrated simultaneous exfoliation and crystallization of lepidocrocite in basic aqueous solution. The obtained ultrathin nanosheets exhibited a much lower Néel temperature (18.3 K) than bulk lepidocrocite and weak ferromagnetic behavior below this temperature.     

Ultrathin FeSe2 Nanosheets: Controlled Synthesis and Application as a Heterogeneous Catalyst in Dye‐Sensitized Solar Cells

Two‐dimensional (2D) semiconducting nanosheets have emerged as an important field of materials, owing to their unique properties and potential applications in areas ranging from electronics to catalysis. However, the controlled synthesis of ultrathin 2D nanosheets remains a great challenge, due to the lack of an intrinsic driving force for anisotropic growth. High‐quality ultrathin 2D FeSe₂ nanosheets with average thickness below 7 nm have been synthesized on large scale by a facile solution method, and a formation mechanism has been proposed. Due to their favorable structural features, the as‐synthesized ultrathin FeSe₂ nanosheets exhibit excellent electrocatalytic activity for the reduction of triiodide to iodide and low charge‐transfer resistance at the electrolyte–electrode interface in dye‐sensitized solar cells (DSSCs). The DSSCs with FeSe₂ nanosheets as counter electrode material achieve a high power conversion efficiency of 7.53 % under a simulated solar illumination of 100 mW cm^?2 (AM 1.5), which is comparable with that of Pt‐based devices (7.47 %).     

Misfit‐Layered Bi1.85Sr2Co1.85O7.7−δ for the Hydrogen Evolution Reaction: Beyond van der Waals Heterostructures

Recent research on stable 2D nanomaterials has led to the discovery of new materials for energy‐conversion and energy‐storage applications. A class of layered heterostructures known as misfit‐layered chalcogenides consists of well‐defined atomic layers and has previously been applied as thermoelectric materials for use as high‐temperature thermoelectric batteries. The performance of such misfit‐layered chalcogenides in electrochemical applications, specifically the hydrogen evolution reaction, is currently unexplored. Herein, a misfit‐layered chalcogenide consisting of CoO₂ layers interleaved with an SrO–BiO–BiO–SrO rock‐salt block and having the formula Bi_1.85Sr₂Co_1.85O_7.7?δ is synthesized and examined for its structural and electrochemical properties. The hydrogen‐evolution performance of misfit‐layered Bi_1.85Sr₂Co_1.85O_7.7?δ, which has an overpotential of 589 mV and a Tafel slope of 51 mV per decade, demonstrates the promising potential of misfit‐layered chalcogenides as electrocatalysts instead of classical carbon.     

Photochromic Metal–Organic Frameworks: Reversible Control of Singlet Oxygen Generation

The controlled generation of singlet oxygen is of great interest owing to its potential applications including industrial wastewater treatment, photochemistry, and photodynamic therapy. Two photochromic metal–organic frameworks, PC‐PCN and SO‐PCN, have been developed. A photochromic reaction has been successfully realized in PC‐PCN while maintaining its single crystallinity. In particular, as a solid‐state material which inherently integrates the photochromic switch and photosensitizer, SO‐PCN has demonstrated reversible control of ¹O₂ generation. Additionally, SO‐PCN shows catalytic activity towards photooxidation of 1,5‐dihydroxynaphthalene.     

Vanadium‐Doped WS2 Nanosheets Grown on Carbon Cloth as a Highly Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Two‐dimensional transition‐metal dichalcogenides have been widely studied as electrocatalysts for the hydrogen evolution reaction (HER). However, limited active sites and poor conductivity hinder their application. To solve these disadvantages, heteroatom doping has attracted wide attention because it can not only increase the active sites but also affect the intrinsic catalytic properties of the electrocatalyst. Herein, we grew vanadium‐doped WS₂ nanosheets on carbon cloth (V‐WS₂/CC) as an electrocatalyst for HER under acidic and alkaline conditions. With a proper vanadium doping concentration, the electrochemical surface areas of V_0.065‐WS₂/CC were 9.6 and 2.6 times as large as that of pure WS₂ electrocatalyst under acidic and alkaline conditions, respectively. In addition, the charge‐transfer resistance also decreased with moderate vanadium doping. Based on this, the synthesized vanadium‐doped WS₂ nanosheets exhibited good stability with high HER catalytic activity and could reach a current density of 10 mA cm⁻² at overpotentials of 148 and 134 mV in 0.5 m H₂SO₄ and 1 m KOH, respectively. The corresponding Tafel slopes were 71 and 85 mV dec⁻¹. Therefore, our synthesized vanadium‐doped WS₂ nanosheets can be a promising electrocatalyst for the production of hydrogen over a wide pH range.     

二维石墨相氮化碳纳米片的制备及其在光催化领域的研究进展

二维(2D)层状石墨型氮化碳纳米片(CNNS)由于具有各向异性的2D几何形态和芳香族p-π共轭骨架,高度开放的平面结构、超高的比表面积、增强的电子迁移速率和与层厚度相关可调的半导体带隙等特征,是目前2D层状材料的研究热点之一。 本文综述了近年来氮化碳纳米片的各种制备方法、功能化改性和应用,涉及环保、能源转换及生物传感等领域。 最后指出进一步探索制备高质量氮化碳纳米片的新方法以及拓展其在光催化领域的应用是未来研究的重点。     

黏土负载镍的纳米片高效芳烃加氢催化剂

以天然层状黏土蒙脱石（MMT）为前体,通过液相沉积-沉淀将镍物种引入水溶液中剥离为MMT纳米片表面的简易方法制得Ni/MMT纳米片。该Ni/MMT纳米片由于是二维（2D）结构,利于芳烃及其加氢产物的传质扩散,相比Ni/SBA-15和Ni/γ-Al₂O₃催化剂,具有更为高效的芳烃加氢性能,且在镍负载量高达18.5%时,其四氢萘加氢的转化频率（TOF）达到最高值。     

Two‐Dimensional Core‐Shelled Porous Hybrids as Highly Efficient Catalysts for the Oxygen Reduction Reaction

Two‐dimensional (2D) transition‐metal dichalcogenides (TMDs) have drawn much attention due to their unique physical and chemical properties. Using TMDs as templates for the generation of 2D sandwich‐like materials with remarkable properties still remains a great challenge due to their poor solvent processability. Herein, MoS₂‐coupled sandwich‐like conjugated microporous polymers (M‐CMPs) with high specific surface area were successfully developed by using functionalized MoS₂ nanosheets as template. As‐prepared M‐CMPs were further used as precursors for preparation of MoS₂‐embedded nitrogen‐doped porous carbon nanosheets, which were revealed as novel electrocatalysts for oxygen reduction reaction with mainly four‐electron transfer mechanism and ultralow half‐wave potential in comparison with commercial Pt/C catalyst. Our strategy to core–shelled sandwich‐like hybrids paves a way for a new class of 2D hybrids for energy conversion and storage.     

A Surfactant‐Free and Scalable General Strategy for Synthesizing Ultrathin Two‐Dimensional Metal–Organic Framework Nanosheets for the Oxygen Evolution Reaction

Metal–organic framework (MOFs) two‐dimensional (2D) nanosheets have many coordinatively unsaturated metal sites that act as active centres for catalysis. To date, limited numbers of 2D MOFs nanosheets can be obtained through top‐down or bottom‐up synthesis strategies. Herein, we report a 2D oxide sacrifice approach (2dOSA) to facilely synthesize ultrathin MOF‐74 and BTC MOF nanosheets with a flexible combination of metal sites, which cannot be obtained through the delamination of their bulk counterparts (top‐down) or the conventional solvothermal method (bottom‐up). The ultrathin iron–cobalt MOF‐74 nanosheets prepared are only 2.6 nm thick. The sample enriched with surface coordinatively unsaturated metal sites, exhibits a significantly higher oxygen evolution reaction reactivity than bulk FeCo MOF‐74 particles and the state‐of‐the‐art MOF catalyst. It is believed that this 2dOSA could provide a new and simple way to synthesize various ultrathin MOF nanosheets for wide applications.     

Enhanced Catalytic Activity in Liquid‐Exfoliated FeOCl Nanosheets as a Fenton‐Like Catalyst

A facile liquid‐phase exfoliation method to prepare few‐layer FeOCl nanosheets in acetonitrile by ultrasonication is reported. The detailed exfoliation mechanism and generated products were investigated by combining first‐principle calculations and experimental approaches. The similar cleavage energies of FeOCl (340 mJ m^?2) and graphite (320 mJ m^?2) confirm the experimental exfoliation feasibility. As a Fenton reagent, FeOCl nanosheets showed outstanding properties in the catalytic degradation of phenol in water at room temperature, under neutral pH conditions, and with sunlight irradiation. Apart from the increased surface area of the nanosheets, the surface state change of the nanosheets also plays a key role in improving the catalytic performance. The changes of charge density, density of states (DOS), and valence state of Fe atoms in the exfoliated FeOCl nanosheets versus plates illustrated that surface atomistic relationships made the few‐layer nanosheets higher activity, indicating the exfoliation process of the FeOCl nanosheets also brought about surface state changes.     

Nanocavity-assisted single-crystalline Ti3+ self-doped blue TiO2(B) as efficient cocatalyst for high selective CO2 photoreduction of g-C3N4

Two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) has invoked significant interest for photocatalytic applications for its excellent features such as high surface area, visible light absorption, and easy transportation of photogenerated charge carriers, but the most reported g-C₃N₄ show relatively low photoactivity due to inferior conductivity and rapid recombination of carriers. These can be overcome by inducing porosity in g-C₃N₄, followed by exfoliation and combining with other materials. Herein, we synthesize nanocavity-assisted oxygen-deficient Ti³⁺ self-doped blue TiO₂(B) nanorods (BT) and integrate them on exfoliated porous g-C₃N₄ (PCN). The synthesized materials are tested for photocatalytic conversion of CO₂ into solar fuels (H₂, CO, and CH₄). The fabricated BT/PCN heterostructures exhibit higher photocatalytic CO₂ conversion activity and 92% CO-evolving selectivity than BT and PCN. The enhancement in activity of BT/PCN can be attributed to the efficient separation and transportation of charge carriers, facilitated by the unique properties of BT, PCN, and their synergistic interactions. We believe that these results can contribute to the improvement of cost-effectiveness, feasibility, and overall performance for real photocatalytic systems.     

The Rapid Exfoliation and Subsequent Restacking of Layered Titanates Driven by an Acid–Base Reaction

Two‐dimensional (2D) (hydro)oxide materials, that is, nanosheets, enable the preparation of advanced 2D materials and devices. The general synthesis route of nanosheets involves exfoliating layered metal (hydro)oxide crystals. This exfoliation process is considered to be time‐consuming, hindering their industrial‐scale production. Based on in situ exfoliation studies on the protonated layered titanate H_1.07Ti_1.73O₄?H₂O (HTO), it is now shown that ion intercalation‐assisted exfoliation driven by chemical reaction provides a viable and fast route to isolated nanosheets. Contrary to the general expectation, data indicate that direct exfoliation of HTO occurs within seconds after mixing of the reactants, instead of proceeding via a swollen state as previously thought. These findings reveal that ion intercalation‐assisted exfoliation driven by chemical reaction is a promising exfoliation route for large‐scale synthesis.