Two-dimensional materials exhibit immense latent capacity in many domain with excellent performance, and monolayer MoSi₂N₄ materials have non-magnetic semiconductors and good stability. In this paper, first principles calculations based on density functional theory are used to study the photoelectric properties of intrinsic two-dimensional MoSi₂N₄ in nitrogen, silicon and molybdenum vacancies. The results show that compared with the intrinsic two-dimensional MoSi₂N₄, the band gap of the defective structure of the outer nitrogen and molybdenum atoms is greatly reduced, while the band gap of the inner nitrogen and silicon atomic defect structures is 0.781 eV and 0.736 eV, respectively. Moreover, the inner nitrogen defect changes the conduction type of two-dimensional MoSi₂N₄ from the original P-type to N-type semiconductor. Optical properties: Each defect structure causes different degrees of redshift in 2D MoSi₂N₄. Two-dimensional MoSi₂N₄ has excellent material properties, and the study of optoelectronic properties is of great significance for the new generation of optoelectronic devices.

MXene (Ti₃C₂T_x) is a new two-dimensional transition metal carbide/nitride discovered in 2011. It has attracted much attention in the field of battery in recent years because of its unique graphene-like layered structure, good metal conductivity, excellent hydrophilicity and adjustable layer spacing. This paper mainly summarizes the relatively mature synthesis strategies and preparation methods of MXene (Ti₃C₂T_x) and its composites, and prospects the application research progress of Ti₃C₂T_x composites in the field of batteries, hoping to provide scientific and theoretical reference for the preparation of high-performance MXene electrode materials and their application in ion batteries.

Based on the new emerging two-dimensional (2D) material of SiP₂, this work proposes three novel 2D materials: monolayer SiAs₂, α-SiAsP and β-SiAsP by the first-principles calculation of density functional theory. Electrostatic potential calculation shows that the three materials are asymmetric in the directions perpendicular to the plane, and are Janus materials. The above materials possess high structural stability and are indirect semiconductors with band gap of 2.21, 2.43 and 1.76 eV, respectively. More interestingly, they can effectively absorb visible as well as ultraviolet light. Moreover, β-SiAsP is even capable of absorbing near-infrared light. Therefore, 2D monolayer SiAs₂, α-SiAsP and β-SiAsP Janus materials have certain application prospects in the field of optics and electronics.

The two-dimensional porous h-BN material is one of the potential CO₂ adsorption materials due to its high specific surface area and abundant surface defects. However, the controllable preparation of two-dimensional porous h-BN with high quality and high specific surface area remains a current problem. In this paper, two-dimensional porous h-BN materials were synthesized with borax (Na₂B₄O₇) and melamine (C₃H₆N₆) as raw materials assist molten salt method. Molten salt can provide a liquid phase reaction environment with high migration and diffusion rate and high activity in the initial stage of h-BN formation. The effects of molten salt type and synthesis temperature on the composition, morphology, pore structure and CO₂ adsorption properties of the product were investigated. The results show that the coexistence of h-BN and r-BN were obtained by using KCl as molten salt, while h-BN with higher purity was obtained by using MgCl₂ as molten salt. Compared with KCl, MgCl₂ molten salt could effectively reduce the synthesis temperature of two-dimensional h-BN to 1 000 ℃, and the product had a higher purity and specific surface area. The specific surface area and CO₂ adsorption capacity of h-BN prepared at 900 ℃ could reach 281.78 m²/g and 7.69 cm³/g, respectively.

Searching for clean and efficient energy has become the priority goal of human sustainable development. As a green and efficient energy source, hydrogen energy is now the focus of the world. So far, there exists certain safety problems in the commonly used hydrogen storage methods such as compressing hydrogen into gas cylinders with high pressure, low-temperature liquefaction and so on. Therefore, the solid hydrogen storage method has received extensive attention. Among them, a large number of exploratory researches have been conducted on the lightweight high-performance solid materials such as MXene which is a new two-dimensional material. As a result, they found out that the maximum hydrogen adsorption capacity of Ti₂C MXene can reach 8.6 wt%, which is much higher than that (5.5 wt%) of metal-based hydrides specified by the U.S. Department of Energy in 2015. Despite the great potential of MXene, its applications in hydrogen storage are not fully explored yet. In this paper, we will introduce the latest research results and application directions of MXene as a hydrogen storage material.

The two-dimensional material MXene with layered structure has attracted the attention of most researchers due to its outstanding conductivity, good hydrophilicity and rich surface chemical structure. This paper focuses on the advanced preparation methods and processes of transition metal carbonitrides, and reviews the research progress of their electrical aspects (including supercapacitors, battery materials and electrocatalysis). In MXene supercapacitors, compared with conventional aqueous electrolytes, organic electrolytes or ionic electrolytes can often provide higher output voltage, resulting in higher energy density. At the same time, the chemical properties of solvents also have a great influence on the molecular/ionic arrangement in MXene. As far as mxene based battery materials are concerned, the layered structure prepared by changing the assembly method of mxene sheet and electrode manufacturing method can prevent aggregation and reaccumulation, and the introduction of cation vacancy can also effectively improve the performance of MXene based battery materials. In addition, several strategies to improve the performance of MXene based materials for electrocatalytic water decomposition are discussed. The purpose of this paper is to review the preparation, structure, application and optimization of MXene in electricity, and to discuss the future research direction and possible challenges.

MXene materials are inorganic compounds composed of pre-transition metal carbon and nitride. Two-dimensional MXene and its composites have graphene-like lamellar structure, high specific surface area, excellent electrical conductivity and abundant surface active sites, which have become a research hotspot in the field of materials in recent years. This paper focuses on the application prospects of two-dimensional MXene materials in the field of gas sensors, and reviews from the perspectives of MXene and gas sensitivity. It focuses on the preparation methods and sensor performance of MXene and its (inorganic/organic) composite materials as gas-sensitive materials. The opportunities and challenges in material design strategy and sensitivity mechanism of two-dimensional MXene in gas sensitive field are proposed, which can provide reference for the potential application of this kind of new materials in gas sensitive field.

MXenes, a novel family of two-dimensional transition metal carbides/nitrides, as two-dimensional materials, have large specific surface areas and diverse surface terminations. The surface of MXenes can adsorb gas molecules, which can change the conductivity of MXenes. Hence, MXenes can be used as novel gas sensitive materials. This paper reviews the gas sensing properties and applications of MXenes (Ti₃C₂ MXene, V₂C MXene, Mo₂C MXene and etc.) from the theoretical and experimental perspectives, summarizes the gas responses of different MXenes, analyzes the gas sensitive mechanisms, concludes the advantages and disadvantages of MXenes as gas sensitive materials and outlooks the future applications of MXenes in the area of gas sensors.

Using ammonium molybdate as molybdenum source and thiourea as sulfur source, binary planar CdS / MoS₂ heterojunction was prepared by hydrothermal method. The heterojunctions were characterized by XRD, SEM, TEM, PL and UV-vis techniques. The results showed that the heterojunction (the mass fractions of MoS₂ were 1%, 5% and 10%, respectively) can effectively improve the visible light absorption intensity of CdS. The photogenerated carriers and holes were effectively separated, thus the composite catalyst exhibited excellent photocatalytic performance. The performance of CdS/MoS₂-10% was the best . The photocatalytic degradation of 10 mg samples to 20 mg/L Roda min B can reach 99%. The catalytic activity of the binary CdS/MoS₂ heterojunction did not decay significantly in the five-cycle experiment.

The structural and electronic properties of the binary Ⅳ-Ⅵ chalcogenides MXs (GeS, GeSe, GeTe, SnS, SnSe, and SnTe) are researched by using density functional theory. The energy band structures, bandgaps, and Fermi level of monolayer MXs are investigated under the external in-plane biaxial strains in a range of -5%-5%. The band structure of monolayer MXs with strains is similar to those without strains, while the bandgaps change so sharply. The bandgap variation of monolayer MXs induced by compressive strain is larger than the corresponding tensile strain. The indirect-to-direct- bandgap-transformation of GeSe, GeTe, SnSe, and SnTe can be obtained while the strain is enforced. The Fermi level of monolayer MXs monotonically decreases with increasing the values of strain ε, and it can be seen that compressive strain is more effective than the corresponding tensile strain. We hope the convertibility electronic properties of monolayer MXs by the strain is helpful to the experimentally on the electronic and optical devices.

Two-dimensional nano tungsten disulfide has attracted the domestic and foreign researchers for the extraordinary layer structure, tunable gap, stabled physical and chemical properties. The latest progress of the two-dimensional nano tungsten disulfide is summarized, and the crystal structure, optical properties and band structure of the tungsten disulfide are primarily introduced. And then the preparation method of two-dimensional nano tungsten disulfide is listed, and the application of two-dimensional nano tungsten disulfide in the field of photocatalyst, photo detector, lubricant, and field effect transistor is summarized. Eventually, the challenges and opportunities of two-dimensional nano tungsten disulfide are prospected.

Dimensional transition metal carbides/nitrides (MXene) obtained by removing the MAX phase A layer by liquid phase etching and other methods is a new member of the two-dimensional material family. The unique two-dimensional structure and surface chemical composition make it show good metal conductivity, hydrophilicity, excellent flexibility and ion intercalability, which shows great potential in the research and application field of supercapacitors and has attracted wide attention. But MXene still has many problems. First, the flakes are easy to stack, which greatly reduces the effective contact area of the material and the electrolyte. During the etching process, the position where the chemical bond is broken has high activity and easily reacts to form surface groups, which has a greater influence on the electrochemical performance. The use of strong corrosive liquids in the synthesis process will also cause many problems such as safety and environment. In this article, the structure, properties and preparation methods of MXene were briefly summarized. The research progress and direction of MXene in the field of supercapacitors in recent years were reviewed. It aimed to find ideas to solve many problems of MXene, looking forward to providing references for the preparation of high-performance MXene supercapacitor electrode materials.

Intrinsic defects are the most common defects in semiconductors. The study of the electrical and magnetic properties of intrinsic defects under the condition of charging is of great importance to the in-depth understanding of the properties of semiconductor materials. In this paper, based on the density functional theory, the intrinsic electronic structure, carrier effective mass, elastic modulus, Young's modulus and Poisson's ratio of two-dimensional hexagonal boron nitride (h-BN) were firstly calculated, and it was found that the carrier effective masswas anisotropic and the mechanical properties were isotropic. Then, the structure, electrical and magnetic properties of four kinds of intrinsic defects (V_B, V_N, B_N, N_B) in the most stable valence state of h-BN were discussed in depth. Combined with electron coordination configuration and spin state density, the magnetic moment generation mechanism of various defects in different valence states was explained.

Doping plays a key role in improving the carrier concentration of semiconductor materials and the performance of semiconductor devices. Theoretically, the p-type doping in semiconductor materials can be predicted by calculating the charged defect formation energy and charge transition energy levels. In this paper, based on the generalized gradient approximation theory and the method of first principles, combined with two-dimensional charged defect correction technology, we used the VASP to systematically calculate several doping system in two-dimensional hexagonal boron nitride (h-BN), including X_B system (X=Be, Mg, Ca, Sr) and Y_N system (Y=C, Si, Ge).The results show that the SiN defect has a quasi-shallow ionization energy of 0.8 eV, while the other six defects are all deep, unable to provide effective p-type carriers for h-BN. However, SiN has high defect forming energy, so it can only be added into h-BN by ion implantation and other non-equilibrium methods.

Two-dimensional transition metal carbon/nitride (MXene) has a graphene-like structure, and microscopically exhibits lamellar and various surface groups. It has good electrical conductivity, ion transport and high hydrophilic properties, and becomes ideal electrode material for supercapacitor. The MXene layer and layer, which are prone to collapse and stacking, and the presence of functional groups are detrimental to the performance as an electrode material. It would have great application prospects, if its electrochemical performance could be improved by heat treatment, ion intercalation and carbon composites. In this paper, the preparation methods of MXene materials were firstly introduced, and then the effects of surface modification and structure optimization on the electrochemical performance of MXene supercapacitors were summarized. Finally, the research prospects of MXene materials on supercapacitors were prospected.

The two-dimensional perovskite material was synthesized by using a cooling hot saturated solution method with n-butyl iodide amine (BAI) as an organic element and lead iodide (PbI₂) as an inorganic element. The effects of different factors on the yield and crystal quality of the synthesized perovskites were studied by adjusting the ratio of BAI to PbI₂ and the reaction temperature. The synthesized two-dimensional perovskite materials were characterized by SEM, XRD, UV-visible absorption and fluorescence spectroscopy. The optimum reaction conditions for the preparation of two-dimensional BA₂PbI₄ by cooling hot saturated solution method were as follows: with hydriodic acid as solvent, m(BAI)∶m(PbI₂)=2.5∶1, water bath heating temperature of 85 ℃, and water bath time of 120 min.

The two-dimensional layered material is a planar material with a single atomic layer or several atomic layer thicknesses. It has special physical and chemical properties and has important application prospects in the fields of photoelectric functional devices, adsorption and separation, and catalysis. It is the frontier of international research and one of the hotspot areas. Among them, graphene is the first two-dimensional material that investigator have paid attention to, and the graphene-like two-dimensional photoelectric functional materials mainly composed of transition metal sulfides have also been widely studied. The discovery of black phosphorus in recent years also has greatly promoted the research and development of two-dimensional optoelectronic materials. In this paper, the research on graphene and graphene-like sulfides in two-dimensional optoelectronic materials and the application status of their optoelectronic functional devices were briefly reviewed, and their application trends were prospected, which provided reference for the research of photovoltaic materials research.

In this paper, the graphene-like two-dimensional Ti₃C₂T_x was prepared by an improved method. Firstly, Ti₃AlC₂ powders were etched by hydrofluoric acid, then intercalated in dimethyl sulfoxide with the assistance of the surfactant cetyl trimethyl ammonium bromide, and finally subjected to ultrasonic treatment. XRD tests showed that the intercalation agent molecules were more likely to enter the Ti₃C₂T_x layer due to the intercalation of the surfactant, which significantly increased the interlayer spacing and reduced the interaction between the layers, facilitating the delamination. Nitrogen adsorption and desorption experiments confirmed that the Ti₃C₂T_x prepared by this method exhibited a higher specific surface area and pore volume. Electrochemical tests showed that the symmetrical capacitor using Ti₃C₂T_x as electrode materials exhibited a higher specific capacitance, the specific capacitance at a current density of 0.5 A/g was 75.0 F/g. And when the charging current was increased to 4 A/g, its capacitance was maintained at 57.0 F/g. After 2 500 charge and discharge cycles, the specific capacitance of Ti₃C₂T_x material was 61.5 F/g at a current density of 1 A/g, and the capacitance retention was 87.0%.

Two-dimensional materials usually have a layered, lamellar, or ribbon-like unique microstructure. Due to this special structure, two-dimensional materials have excellent optical, mechanical, and electrical properties. Because of their high conductivity, large specific surface area, environmental protection, and low cost, biomass carbon materials have become a hot topic in the research of energy storage devices. In this paper, based on the application of biomass two-dimensional carbon materials in the field of lithium-ion batteries and supercapacitors, the research progress was summarized, and the research prospects of two-dimensional carbon materials of biomass was prospected.

Graphene-like two-dimensional layered nanomaterials have recently drawn great attention in the field of biomedicine. However, the biological properties and applications of these 2D nanomaterials have not been fully understood. In this paper, the small-sized 2D layered nanomaterials including MoS₂ and WS₂ were prepared by using the combination of sonication and solvothermal treatment of bulk MoS₂ and WS₂ powder. The experiments of ascorbic acid catalytic oxidation demonstrate that the fabricated nanomaterials possess oxidase-like activity and MoS₂ exhibits stronger activity than WS₂. Further experiment shows the MoS₂ and WS₂ nanomaterials can cause the oxidation of glutathione, thereby exhibiting antimicrobial activity against both gram-negative and gram-positive bacteria. And the MoS₂ shows more efficient antimicrobial activity than WS₂, which is in accordance with the activity of oxidases. In this work, theoretical guidance for the research and application of the 2D layered nanomaterials as potential enzyme mimics were provided.

Due to their unique mechanical, optical and electrical properties, two-dimensional (2D) layered materials such as graphene and transitional metal dichalcogenides (TMDs) have been gaining strong interests and they have great potentials for applications in flexible devices. However, the controllable synthesis is the prerequisite for their applications. Here, 2D MoS₂ was synthesized by chemical vapor deposition (CVD) method. In this study, the influence of substrate placement on the synthesis of 2D MoS₂ was investigated. The results show that under the same experimental conditions, the 2D MoS₂ prepared by the substrate placement of face-up and face-down have different shapes and coverage rates. Despite these, the structure and the photoluminescence properties of the monolayer MoS₂ achieved by different placements of the substrate are identical. The results would be helpful to design the procedures for controllable synthesis of TMDs.

An improved liquid-phase exfoliation method for the preparation of MoS₂ 2D nanosheets combined ball-milling and high-speed shearing was reported. During the ball-milling process, CaCO₃ particles were incorporated as micro milling balls and drops of NMP was also added as liquid lubrication. The mixture of MoS₂, CaCO₃ and NMP was ball-milled at 400rpm for a certain time. After that, the mixture was washed and dissolved in 45% ethanol/water with proper amount of HCl to get rid of CaCO₃. Then high-speed shearing was used to exfoliate the ball-milled MoS₂ nanoparticles, and high-speed centrifugation was used to precipitate the bulk MoS₂ particles in the mixture, thus the supernatant full of MoS₂ nanosheets was obtained. Malvern Zetasizer, SEM, AFM, TEM, Raman was used to characterize the obtained MoS₂ nanosheets. It turned out that the MoS₂ 2D nanosheets were successfully obtained using this method, and the highest yield 54.43 mg/ml was achieved.

Hierarchical mesoporous CeO2 nanosheets were prepared by using camellia flower petal as biotemplate through thermal decomposition. For characterization of texture,X-ray diffraction spectroscopy (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscope (AFM), UV-Vis diffuse reflectance spectra (UV-Vis/ DRS) and nitrogen adsorption-desorption measurements were adopted. The results demonstrate that the biomorphic structure of fluorite structure CeO2 nanosheets with the thickness of ca. 6 nm was obtained. There exists mesopores with pore size of about 15 nm on the surface of the CeO2 nanosheets. Hierarchical mesoporous CeO2 nanosheets exhibit a clear red shift (35 nm) comparing with bulk CeO2, which could be excited by visible irradiation and enhance the visible activity. Hierarchical mesoporous CeO2 nanosheets display the superior photocatalytic activity for the degradation of methylene blue under sunlight irradiation, with a degradation rate as high as 98%. It was contributed to the smaller crystallite size, enhanced higher surface area of the ceria nanosheets.

Nano insulations have excellent insulating performance and find wide application in hypersonic vehicle thermal protection technologies. In this study a two dimensional computational model based upon phonon radiative transfer equation for phonon transport in the solid of nano insulations is established. The discrete ordinate method is used to solve the transport equation numerically. The size effects in the longitudinal and transverse conductivity are numerically simulated for a 2D silica nanowire. Results show that obvious size effect in the conductivity exists in the 2D nanowire and the conductivity is mainly influenced by the wire diameter. For the nanowire with the diameter between 2nm~4nm considered, its thermal conductivity is 15% less than the bulk material. Results obtained in this study may be useful in recognizing the heat transfer mechanism in solids of nano insulations

Viscosimetric method and two-dimensional infrared correlation spectroscopy were used to study the compatibility and interaction of collagen and hydroxypropyl methylcellulose (HPMC) blends in the present work. It was found that collagen/HPMC blends were compatible as HPMC content was below 30% by viscometric determination, while the blends were incompatible when HPMC content was above 50%. The synchronous negative cross-peaks between the stretching vibrations of C-O(H) of HPMC at 1061 cm-1 and amide bands of collagen derived from stretching vibrations of C=O at 1660 cm-1, wagging of N-H at 1553 cm-1 and in-plane deformation of N-H at 1238 cm-1, which were observed from two-dimensional infrared correlation spectroscopy, indicated that the O-H of HPMC interacted with collagen as HPMC content was less than 30%. However, as HPMC content was exceeded 30%, the intensity of negative cross-peak was decreased in synchronous correlation spectra while the intensity of cross-peak at 1061 cm-1 was enhanced significantly, indicating that the hydrogen bonding interaction between collagen and HPMC molecules became weaker; on the contrary, the hydrogen bonding formed amongst HPMC molecules tended to be enhanced.

Alkali-solubilized collagen solution cross-linked with N-hydroxysuccinimide activated adipic acid (NHS-AA) ester. The effect of NHS-AA on the secondary structure of alkali-solubilized collagen was examined. The infrared bands, determined by the fourier-transform infrared spectroscopy (FT-IR), did not reflect characteristics which were caused the amount of cross-linking, but the results from two-dimensional infrared correlation spectroscopy (2D-IR) indicated that the positive synchronous cross-peaks, derived from stretching vibrations of C=O at 1672 cm-1, C-N stretching vibrations and wagging of N-H at 1554 cm-1 and in plane deformation of N-H at 1241cm-1 of collagen, were indicative of local conformational changes of collagen. The order of secondary structure changes of cross-linked collagen was amide III than amide I than amide II than -CH3 than -CH-. It was shown that the microcosmic information of a change in dynamic structure could be provided for cross-linked collagen with the interruption of the cross-linker concentration. These fundamental data should provide available information for understanding of the relationship between the structure and function of cross-linked collagen.

Based on the ultrasonic immersion transmission technique, the directed band gaps of two-dimensional (2D) phononic crystal consists of a square array of steel cylinders in water were measured experimentally along the Γ-X and Γ-M directions of first irreducible Brillouin zone. The relations of layers and first band gaps stability can be analyzed in detail. This is better advantage of design for finite-sized 2D phononic crystal or acoustic devices. An excellent agreement between the frequency range of overlapping transmission spectra of acoustic waves and complete band gap of 2D phononic crystal for theoretical predict with plane wave expansion method is observe.