Due to their extraordinary properties, boron nitride nanosheets (BNNSs) have great promise for many applications. However, the difficulty of their efficient preparation and their poor dispersibility in liquids are the current factors that limit this. A simple yet efficient sugar‐assisted mechanochemical exfoliation (SAMCE) method is developed here to simultaneously achieve their exfoliation and functionalization. This method has a high actual exfoliation yield of 87.3%, and the resultant BNNSs are covalently grafted with sugar (sucrose) molecules, and are well dispersed in both water and organic liquids. A new mechanical force–induced exfoliation and chemical grafting mechanism is proposed based on experimental and density functional theory investigations. Thanks to the good dispersibility of the nanosheets, flexible and transparent BNNS/poly(vinyl alcohol) (PVA) composite films with multifunctionality is fabricated. Compared to pure PVA films, the composite films have a remarkably improved tensile strength and thermal dissipation capability. Noteworthy, they are flame retardant and can effectively block light from the deep blue to the UV region. This SAMCE production method has proven to be highly efficient, green, low cost, and scalable, and is extended to the exfoliation and functionalization of other two‐dimensional (2D) materials including MoS2, WS2, and graphite.

Among two-dimensional (2D) transition-metal dichalcogenides (TMDCs), platinum diselenide (PtSe 2 ) stands in a distinct place due to its fancy transition from type-II Dirac semimetal to semiconductor with a thickness variation from bulk to monolayer (1 ML) and the related versatile applications especially in mid-infrared detectors. However, achieving atomically thin PtSe 2 is still a challenging issue. Herein, we have designed a facile chemical vapor deposition (CVD) method to achieve the synthesis of atomically thin 1T-PtSe 2 on an electrode material of Au foil. Thanks to the high crystalline quality, we have confirmed the complete transition from semimetal to semiconductor from trilayer (3 ML) to 1 ML 1T-PtSe 2 . More importantly, we have found that such atomically thin 1T-PtSe 2 can serve as perfect electrocatalysts, featured with a record high hydrogen evolution reaction (HER) efficiency (comparable to traditional Pt catalyst). Our work is helpful toward the large-scale synthesis, exotic physical property exploration, and intriguing application development of atomically thin TMDCs.

2D metallic TaS is acting as an ideal platform for exploring fundamental physical issues (superconductivity, charge-density wave, etc.) and for engineering novel applications in energy-related fields. The batch synthesis of high-quality TaS nanosheets with a specific phase is crucial for such issues. Herein, the successful synthesis of novel vertically oriented 1T-TaS nanosheets on nanoporous gold substrates is reported, via a facile chemical vapor deposition route. By virtue of the abundant edge sites and excellent electrical transport property, such vertical 1T-TaS is employed as high-efficiency electrocatalysts in the hydrogen evolution reaction, featured with rather low Tafel slopes ≈67-82 mV dec and an ultrahigh exchange current density ≈67.61 µA cm . The influence of phase states of 1T- and 2H-TaS on the catalytic activity is also discussed with the combination of density functional theory calculations. This work hereby provides fundamental insights into the controllable syntheses and electrocatalytic applications of vertical 1T-TaS nanosheets achieved through the substrate engineering.

The practical application of lithium-sulfur (Li-S) batteries is hindered by their poor cycling stabilities that primarily stem from the "shuttle" of dissolved lithium polysulfides. Here, we develop a nepenthes-like N-doped hierarchical graphene (NHG)-based separator to realize an efficient polysulfide scavenger for Li-S batteries. The 3D textural porous NHG architectures are realized by our designed biotemplating chemical vapor deposition (CVD) approach via the employment of naturally abundant diatomite as the growth substrate. Benefiting from the high surface area, devious inner-channel structure, and abundant nitrogen doping of CVD-grown NHG frameworks, the derived separator favorably synergizes bifunctionality of physical confinement and chemical immobilization toward polysulfides, accompanied by smooth lithium ion diffusions. Accordingly, the batteries with the NHG-based separator delivers an initial capacity of 868 mAh g with an average capacity decay of only 0.067% per cycle at 2 C for 800 cycles. A capacity of 805 mAh g can further be achieved at a high sulfur loading of ∼7.2 mg cm. The present study demonstrates the potential in constructing high-energy and long-life Li-S batteries upon separator modification.

Modulating electronic structure of monolayer transition metal dichalcogenides (TMDCs) is important for many applications and doping is an effective way towards this goal, yet is challenging to control. Here we report the in-situ substitutional doping of niobium (Nb) into TMDCs with tunable concentrations during chemical vapour deposition. Taking monolayer WS2 as an example, doping Nb into its lattice leads to bandgap changes in the range 1.98 eV to 1.65 eV. Noteworthy, 2 electrical transport measurements and density functional theory calculations show that the 4d electron orbitals of the Nb dopants contribute to the density of states of Nb-doped WS2 around the Fermi level, resulting in an n to p-type conversion. Nb-doping also reduces the energy barrier of hydrogen absorption in WS2, leading to an improved electrocatalytic hydrogen evolution performance. These results highlight the effectiveness of controlled doping in modulating the electronic structure of TMDCs and their use in electronic related applications.

This article reviewed the structures, properties and external controls of 2D magnets.

Searching for 2D ferromagnetic materials with a high critical temperature, large spin polarization, and controllable magnetization direction is a key challenge for their broad applications in spintronics. Here, through a systematic study on a series of 2D ternary chalcogenides with first-principles calculations, it is demonstrated that a family of experimentally available 2D CoGa 2 X 4 (X = S, Se, or Te) are half-metallic ferromagnets, and they exhibit high critical temperature, fully polarized spin state, and strain-dependent magnetization direction simultaneously. Following the Goodenough-Kanamori rules, the half-metallic ferromagnetism of CoGa 2 X 4 family is caused by superexchange interaction mediated by CoXCo bonds. The half-metal gaps are large enough (>0.5 eV) to ensure that the half-metallicity is stable against the spin flipping at room temperature. Magnetocrystalline anisotropy energy calculations indicate that CoGa 2 X 4 favor easy plane magnetization. Under achievable biaxial tensile strain (2-6%), the magnetization directions of CoGa 2 X 4 can change from in-plane to out-of-plane, providing a route to control the efficiency of spin injection/detection. Further, the critical temperatures T c of ferromagnetic phase transition for CoGa 2 X 4 are close to room temperature. Belonging to the big family of layered AB 2 X 4 compounds, the proposed CoGa 2 X 4 systems will enrich the available 2D candidates and their heterojunctions for various applications.

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