In recent years, ternary layered carbide/nitride MAX phases and their derived two-dimensional nanolaminates MXenes have attracted extensive attention. The crystal structure of MAX phase is composed of M_n+1X_n unit interleaved with layers of A element. MAX phases combine good properties of metal and ceramic, which makes them promising candidates for high temperature structural materials, friction and wear devices, nuclear structural materials, etc. When etching the A-layer atoms of the MAX phase, the two-dimensional nanolaminates with the composition of M_n+1X_nT_x (T_x is surface termination), i.e. MXene, is obtained. MXenes have wide range of composition, and tunable physical and chemical properties, which endow them great potential in the applications of energy storage devices, electromagnetic shielding materials, and electronic devices, etc. In this paper, the research progress of MAX phase and MXene was introduced in terms of composition and structure, synthesis methods, and properties and application. Furthermore, the research prospects of this large family of materials were discussed.

MXenes—two-dimensional (2D) compounds generated from layered bulk materials, have attracted significant attention in energy storage fields. However, low mass loading of MXenes results in low areal capacity and impedes the practical use of MXenes electrodes. Inspired by natural basswood, an ideal architecture with natural, three-dimensionally (3D) aligned open microchannels was developed for high Ti₃C₂T_x mass loading. Compared with reported Ti₃C₂T_x electrode structure, the 3D porous carbon matrix has several advantages including low tortuosity, high conductivity and good structure stability. The Ti₃C₂T_x assembled with the wood carbon can deliver a high areal capacity of 1983 mF/cm ² at 2 mV/s with a high Ti₃C₂T_x mass loading of 17.9 mg/cm ² when used as electrode for supercapacitors. This work provides a new strategy to develop 3D porous electrodes for MXenes, which can achieve high areal capacity.

With the development of wearable flexible electronic technology, the demand for flexible sensor with high sensitivity and wide sensing range is gradually increasing. The application of suitable conductive materials with high electrical conductivity and high flexibility as sensitive materials for sensors is the key to obtain high performance sensors. In recent years, MXene materials have become very promising sensitive materials due to their good conductivity, high flexibility, good hydrophilicity, and controllable synthesis. The types of MXene-based flexible force sensors, microstructure design of sensitive materials, sensing performance, and sensing mechanism analysis have been expound and summarized in this paper.

Recently, a new type of 2D transition metal carbides or nitrides (MXene) has attracted wide attention due to its large specific surface area, good hydrophilicity, metallic conductivity and other physical and chemical properties. 2D Ti₃C₂T_x MXene was obtained by etching Al layer of Ti₃AlC₂ with LiF and HCl and then mechanically delaminated. And the monolayer Ti₃C₂T_x nanosheets with lateral dimension of 625 and 2562 nm can be prepared by changing the intensity and way of mechanically delamination, as well as the centrifugation rate and time. Then their morphology, structure, composition, and electrochemical performance of Ti₃C₂T_x were studied. The results showed that the specific capacitance of Ti₃C₂T_x with smaller lateral size (<1 μm) can reach 561.9 F/g, higher than that of reported graphene, carbon tube and MnO₂ in the repotted literatures. And the Ti₃C₂T_x electrode still remained 96% of the initial specific capacitance after 10 ⁴ testing cycles.

In recent years, hexagonal boron nitride (h-BN) two-dimensional (2D) atomic crystal has attracted considerable attention due to its unique structure, novel property and potential applications. The synthesis of high quality h-BN determines how far we can go for property research and practical applications. However, the sizes of h-BN domains obtained by mechanical exfoliation were limited to several micrometers. Transition metal substrates are usually used in the CVD growth of 2D h-BN layers, and thus a transfer process is required for fabricating h-BN-based electronic devices. Therefore, it is strongly desirable to directly synthesize 2D h-BN on dielectric substrates. In this article, we review recent process on the direct growth of h-BN by CVD, MOVPE, PVD on different dielectric substrates, including silicon-based substrates, sapphire, quartz, etc. Several approaches, such as, increasing substrate temperature, oxide-assisted nucleation, and surface nitridation were adopted to directly grow h-BN on dielectric substrates. Besides, we also summarized the main applications of 2D h-BN grown on dielectric substrates.

Two dimensional (2D) materials have attracted wide attention due to their ultrathin atomic structure, large specific surface area and quantum confinement effect which are remarkably different from their bulk counterparts. Anisotropic materials are unique among reported 2D materials. Their orientation-dependent physical and chemical properties make it possible to selectively improve the performance of materials. As representative examples, Re-based transition metal dichalcogenides (Re-TMDs) have tunable bandgaps in visible spectrum, extremely weak interlayer coupling, and anisotropic properties in optics and electronics, which make them attractive in the application areas of electronics and optoelectronics. In this riviev, the unique crystal structures and intrinsic properties of the Re-based TMDs semiconductors are introduced firstly, and then the synthetic method is introduced, followed by discussion on the unique physical characterizations and optimized means. Finally, prospects and suggestions are put forward for the preparation and research of ReX₂.

All inorganic perovskite (CsPbX₃) nanocrystals has wide applications in the field of optoelectronic devices due to its excellent photoelectric characteristics, however, stability is still the bottleneck restricting its development. Combining with the current research progress, the BN/CsPbX₃ composite nanocrystals phosphors was synthesized via all-solid-state reactions. During the process, parameters of ball milling, ratio of reactants and other reaction conditions were optimized, thus the BN/CsPbX₃ composite nanocrystals can be stable in the air for more than 60 days. Its luminescence wavelength can cover the range of 417-680 nm with full width at half maximum of 23-47 nm, showing high color purity, and was further used in white LED with high stability and luminance. After placed in the atmosphere for a month, the attenuation of LED luminance is only about 0.7%, and less than 4% deterioration was observed after continuous work of 2 h, showing great working stability.

Given the good electrochemical performance and excellent irradiation stability of two dimensional transition metal carbides (MXenes), the development of MXene-based electrode materials for radionuclide detection is very promising. In this work, Ti₃C₂T_x MXene was activated via an alkalization strategy to form K⁺ intercalated Ti₃C₂T_x (K-Ti₃C₂T_x). Then the modified electrode of K-Ti₃C₂T_x/GCE was prepared on glassy carbon electrode (GCE). Ti₃C₂T_x and K-Ti₃C₂T_x were characterized by XRD, SEM and XPS techniques, and the electrochemical detection performance of K-Ti₃C₂T_x/GCE for trace uranyl ion (UO₂²⁺) was further investigated. Cyclic voltammetry (CV) experiments showed that the electrochemical response of K-Ti₃C₂T_x/GCE modified electrode to UO₂²⁺ increased significantly. Under the differential pulse voltammetry (DPV) scanning at pH 4.0, the K-Ti₃C₂T_x/GCE modified electrode presented a good linear detection relationship for UO₂²⁺ in the uranium concentration range of 0.5-10mg/L. The detection limit of this method is 0.083 mg/L (S/N = 3), with decent stability and repeatability.

SiC ceramics have excellent mechanical properties, but its toughness is relatively low. To enhance the fracture toughness of SiC ceramics, graphene is introduced as fillers. In this study, the silicon carbide-reduced graphene oxide (SiC/rGO) composites with different contents of rGO were fabricated by hot press sintering (HP). Near fully-dense SiC/rGO composite was obtained after being hot-pressed under 2050℃, 40 MPa for 1 h. In addition, the influences of graphene reinforcement on the sintering process, microstructure, and mechanical properties (fracture toughness, bending strength, and Vickers hardness) of SiC/rGO composites were discussed. The three-point flexural strength of 4wt% rGO/SiC composite reached 564 MPa, and the fracture toughness reached 4.02 MPa•m^1/2, which were 6% and 54% higher than those of hot-pressed SiC ceramics, respectively. The flexural strength of the three points of 6wt% rGO/SiC composite was 420 MPa, which was lower than that of hot-pressed SiC ceramics. While its fracture toughness was up to 4.56 MPa•m^1/2, which was 75% higher than that of hot-pressed SiC ceramics. The results of crack propagation show that the toughening mechanism can be ascribed to crack deflection, crack bridging and rGO pullout.

Boron nitride (BN) coatings were prepared using BCl₃-NH₃-H₂-N₂ precursor system by chemical vapor deposition process in a vertically-placed hot wall reactor. The effect of processing parameters on the deposition rates was analyzed. The morphology and microstructure of the BN coating on the surface of the silicon carbide fiber were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscope (XPS) and X-ray diffraction (XRD) . The dominant gas-surface reactions and crucial gas-phase components during BN deposition process were established. The results show that the deposition rates of BN increase gradually with the elevating deposition temperature from 600℃ to 850℃. And at a defined temperature, the deposition rates of BN gradually decrease along the gases flow direction in the deposition area, indicating that the gas-phase components are gradually consumed along the gases flow direction. The deposition rates of BN increase firstly and then decrease with the increase of system pressures, which suggests that the deposition process change from surface reactions control to mass transfer control. The BN deposition rates increase at 1-3 cm away from gases inlet, but decrease after increase firstly at 4-5 cm away from gases inlet as the residence time getting longer. SEM results show that BN coating on the surface of silicon carbide fiber is relatively smooth and dense. The chemical compositions of coating determined by XPS are BN and B₂O₃. XRD results indicate that the deposited BN at 650℃is amorphous. After heat-treatment at 1200℃ for 2 h, it transformed into the hexagonal BN(h-BN). The deposition of BN is achieved by the intermediate gas-phase species composed of Cl₂BNH₂, ClB(NH₂)₂ and B(NH₂)₃ which were generated by the reaction of BCl₃ and NH₃.

In this study, by using dispersions of graphene oxide (GO) and nickel nitrate (Ni(NO₃)₂·6H₂O) with different ratios as precursors, three-dimensional self-supported reduced graphene oxide/NiO composites (3D rGO/NiO) were prepared via a one-step hydrothermal method. The analysis results (XRD, SEM, etc) indicate that NiO nanoparticles are homogeneously dispersed on the surface of graphene layers. The specific capacitance of 3D rGO/NiO composite reaches 1208.8 F·g^-1 at a current density of 1 A·g^-1 when the mass ratio of GO and Ni(NO₃)₂·6H₂O is 1 : 4. With the current density increasing from 0.2 to 10 A·g^-1, the specific capacitance retention of this composite is higher than 72.6%. After 10000 cycles, the specific capacitance of 3D rGO/NiO at a current density of 10 A·g^-1 remained at 93% of the initial specific capacitance. All of these demonstrated that the composite possesses good rate capability and cycle stability. The 3D rGO/NiO composite has excellent electrochemical performances when compared with pure NiO or rGO, which is attributed to the synergistic effect between NiO and rGO.

2D transition metal dichalcogenides (TMDs) have been extensively studied in recent years because of their appealing electrical and optical properties. Both morphology control and bandgap modulation of TMD alloys are critical for their applications in optoelectronics, photonics and nanoelectronics. In this work, the synthesis of vertically aligned ReS_2(1-x)Se_2x alloy nanosheets with tunable compositions on SiO₂/Si substrate was achieved via CVD technology. The resulting ReS_2(1-x)Se_2x nanosheets were obtained by selenizing the vertically aligned ReS₂ nanosheets at various temperatures for different durations. The ReS_2(1-x)Se_2x samples were characterized by XRD, SEM, XPS, HRTEM, elemental mapping, Raman spectra, and UV-Vis-NIR absorption spectra. Experimental results showed that the Se contents in ReS_2(1-x)Se_2x nanosheets can be gradually tuned from x=0 (pure ReS₂) to x=0.86, and the bandgaps of the products were correspondingly modulated from 1.55 eV (800 nm) to 1.28 eV (969 nm). Moreover, the temperature and duration of selenization have huge effect on the morphology of the resulting ReS_2(1-x)Se_2x alloyed nanosheets, as evidenced by SEM observation. The vertical ReS_2(1-x)Se_2x alloy nanosheets may have significant application potential, e. g. , in the electrochemical catalysis, functional electeonic and optoelectronic devices.

Cu/Ti₃C₂T_x composites with Ti₃C₂T_x content of 5vol%, 10vol% and 20vol% were prepared by using a molecular-level mixing process and spark plasma sintering (SPS). Influence of Ti₃C₂T_x content on electrical, mechanical and tribological properties was investigated. The result showed that relative density and electrical conductivity of Cu/Ti₃C₂T_x composites gradually decreased with the Ti₃C₂T_x content increase, while the tensile strength of Cu/Ti₃C₂T_x composites increased at first and then decreased. When the Ti₃C₂T_x content was 5vol%, the tensile strength of Cu/ Ti₃C₂T_x composites increased by 43% than that of pure copper. Tribological properties of Cu/ Ti₃C₂T_x composites were enhanced by the addition of Ti₃C₂T_x. When the Ti₃C₂T_x content was 10vol%, the wear rate of Cu/ Ti₃C₂T_x composites was 2.55×10^-7 mm³/(N·m), which was one magnitude lower than that of pure copper.

The g-C₃N₄/MoS₂ nanosheets/graphene oxide (GO) ternary composite photocatalyst was successfully prepared by a ball milling method. Its structure, morphology and optical property were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Vis absorption spectroscopy (DRS), and photoluminescence spectroscopy (PL), respectively. The results indicated that the heterogeneous structure of MoS₂ nanosheets and g-C₃N₄ were formed on the surface of GO. The photocatalytic activity of the photocatalyst was evaluated by degradation of organic Rhodamine B (RhB) under visible light irradiation. The ternary composite photocatalyst could degrade 96% of RhB within 120 min, about 3, 2.1 and 2.8 times higher than that of the g-C₃N₄, g-C₃N₄/MoS₂ composite and g-C₃N₄/GO composite. Based on the experimental results and the band structure, a possible charge transfer mechanism of ternary composite photocatalyst was proposed.

It is of great importance to enhance the performance of oxide ceramic composite for fulfilling the increasing requirements from modern society. To this end, graphene is very suitable to be exploited as reinforcement for achieving superior performance in oxide ceramic composites, due to its extraordinary mechanical and electrical properties. In this review, the study of graphene based oxide ceramic composite including the processing, densification, microstructure and properties, based on the reports and researches in the past decade. It can be seen that: (1) the incorporation of graphene can generally improve the strength, fracture toughness and strain tolerance of oxide ceramic composite; (2) for the electrical performance, the graphene/oxide ceramic composites show not only low percolation threshold and high electrical conductivity, but also tunable charge carrier type which can be controlled by the oxygen concentration in oxide matrix. Therefore, it is believed that the graphene based oxide ceramic composites are very promising material for the application requiring both advanced mechanical and functional properties.