Herein, a ternary vanadium bronze compound, NaV6O15 was synthesized via a low temperature thermal oxidization of sodium-intercalated V2CTx, which exhibited a higher specific capacity than the precursor V2CTx when used as the anode material for lithium-ion batteries (LIBs). The characterization results showed that the NaV6O15 nanorods spontaneously grew in the interlayers and directly damaged the layered structure of MXene. Moreover, the charge–discharge result demonstrated an initial specific discharge capacity of 350 mAh g−1 under a current density of 50 mA g−1 was achieved and, in particular, a specific capacity of 120 mAh g−1 and a Coulombic efficiency of 100% were maintained after as many as 200 cycles at 1000 mA g−1 without the lattice expansion and deformation of NaV6O15 during the lithium-ion insertion/de-insertion process. According to these results, it is therefore expected that optimizing the process further to oxidize other metal cations intercalated-MXene will exploit other nanostructures employed as the electrode in LIBs and demonstrate immeasurable performance.

Here a novel material for methane adsorption was synthesized and studied, which is a graphene-like two-dimensional (2D) carbide (Ti2C, a member of MXenes), formed by exfoliating Ti2AlC powders in a solution of lithium fluoride (LiF) and hydrochloric acid (HCl) at 40 °C for 48 h. Based on first-principles calculation, theoretically perfect Ti2C with O termination has a specific surface area (SSA) of 671 m2 g−1 and methane storage capacity is 22.9 wt%. Experimentally, 2.85 % exfoliated Ti2C with mesopores shown methane capacity of 11.58 cm3 (STP: 0 °C, 1 bar) g−1 (0.82 wt%) under 5 MPa and the SSA was 19.1 m2 g−1. For Ti2C sample intercalated with NH3·H2O, the adsorbed amount was increased to 16.81 cm3 (STP) g−1 at same temperature. At the temperature of 323 K, the adsorbed amount of as-prepared Ti2C was increased to 52.76 cm3 (STP) g−1. For fully exfoliated Ti2C, the methane capacity was supposed to be 28.8 wt% or 1148 V (STP)v−1. Ti2C theoretically has much larger volume methane capacity than current methane storage materials, though its SSA is not very high.

This paper reports the dry-sliding tribological properties of Ti3SiC2 at room temperature in air, coupled with different counterfaces, including Ti3SiC2, Al2O3, Si3N4, SiC, and GCr15-bearing-steel. Ti3SiC2 exhibited obviously different tribological properties with different sliding counterfaces. The lowest friction coefficient (0.43) and wear rate (2.09×10−4 mm3/Nm) were obtained in the Ti3SiC2/SiC friction pair. Increased friction coefficient (0.63) and wear rate (3.67×10−4 mm3/Nm) were observed if Ti3SiC2 slides against GCr15-bearing-steel. The highest friction coefficient (1.30) was observed in Ti3SiC2/Al2O3 friction pair and the highest wear rate (1.87×10−3 mm3/Nm) was observed in Ti3SiC2/Ti3SiC2 friction pair. Scanning electron microscopy and X-ray photoelectron spectroscopy showed two main wear mechanisms: mechanical wear and oxidation wear. Mechanical wear was the main mechanism for sliding against Ti3SiC2, Si3N4, or Al2O3. Grain removal was a significant tribological character of self-mated Ti3SiC2 friction pair. For Ti3SiC2/SiC friction pair, oxide wear played a more important role and more oxides were formed than those in other friction pairs. Oxide films protected the surface of Ti3SiC2/SiC friction pair from direct contact, and decreased wear rate and friction coefficient.

•Ti3C2 from PLS-Ti3AlC2 was highly oriented compared to that from HP-Ti3AlC2.•Small balls of possible AlF3 attached on the edge of MXene sheets were observed.•MXene is thermally stable in Ar atmosphere up to 800 °C.•A structure of nano-anatase on 2D Ti3C2 was formed by 200 °C oxidization.We investigated the synthesis of quasi-two-dimensional carbide (Ti3C2), with the name of MXene, by immersing Ti3AlC2 in 40% or 49% hydrofluoric acid (HF) at 0 °C, 15 °C or 60 °C. The influences of time, temperature, and source of Ti3AlC2 on the synthesis were researched. It was found that Ti3C2 synthesized from pressureless synthesized Ti3AlC2 was highly oriented compared to that from hot-pressed Ti3AlC2. As-synthesized Ti3C2 could be further exfoliated by intercalation with urea, dimethylsulfoxide or ammonia. From the results of thermogravimetry and differential scanning calorimetry, Ti3C2 MXene with F/OH termination was found to be stable in argon atmosphere at temperature up to 800 °C. In oxygen atmosphere, at 200 °C, parts of MXene layers were oxidized to obtain an interesting structure: anatase nano-crystals were evenly distributed on 2D Ti3C2 layers. At 1000 °C, MXene layers were completely oxidized and anatase phase fully transformed to rutile in oxygen atmosphere.

•2D Ti3C2 after intercalation has larger c and larger lamella thickness.•In-Ti3C2 has capacity close to theoretical capacity with F termination.•In-Ti3C2 has better electrochemical performance than Ex-Ti3C2.Two-dimensional (2D) Ti3C2 was synthesized by the exfoliation of Ti3AlC2 with HF solution and subsequently intercalation with dimethyl sulfoxide. As anode for lithium ion batteries, Ti3C2 after intercalation had an obvious higher capacity than that before intercalation. The capacity can be 123.6 mAh g− 1 at 1C rate with a coulombic efficiency of 47%. It is higher than that of 2D Ti2C and close to the theoretical capacity of Ti3C2 with F termination. It was suggested that MXene with pure F groups may be a way to further improve its Li storage performance.

•Ti3SiC2–cBN composites were really made.•Starting materials: Ti3SiC2 and cBN powder, pressure: 4.5 GPa, temperature: 1050 °C.•The high pressure is to keep Ti3SiC2 rather than cBN in the composites.In this paper, synthesis of novel super hard and high performance composites of titanium silicon carbide–cubic boron nitride (Ti3SiC2–cBN) was evaluated at three different conditions: (a) high pressure synthesis at ~ 4.5 GPa, (b) hot pressing at ~ 35 MPa, and (c) sintering under ambient pressure (0.1 MPa) in a tube furnace. From the analysis of experimental results, the authors report that the novel Ti3SiC2–cBN composites can be successfully fabricated at 1050 °C under a pressure of ~ 4.5 GPa from the mixture of Ti3SiC2 powders and cBN powders. The subsequent analysis of the microstructure and hardness studies indicates that these composites are promising candidates for super hard materials.

Searching for reversible hydrogen storage materials operated under ambient conditions is a big challenge for material scientists and chemists. In this work, using density functional calculations, we systematically investigated the hydrogen storage properties of the two-dimensional (2D) Ti2C phase, which is a representative of the recently synthesized MXene materials ( ACS Nano 2012, 6, 1322). As a constituent element of 2D Ti2C phase, the Ti atoms are fastened tightly by the strong Ti–C covalent bonds, and thus the long-standing clustering problem of transition metal does not exist. Combining with the calculated binding energy of 0.272 eV, ab initio molecular dynamic simulations confirmed the hydrogen molecules (3.4 wt % hydrogen storage capacity) bound by Kubas-type interaction can be adsorbed and released reversibly under ambient conditions. Meanwhile, the hydrogen storage properties of the other two MXene phases (Sc2C and V2C) were also evaluated, and the results were similar to those of Ti2C. Therefore, the MXene family including more than 20 members was expected to be a good candidate for reversible hydrogen storage materials under ambient conditions.

Titanium aluminum carbide (Ti3AlC2 and Ti2AlC) powders were synthesized from TiH2 powders instead of Ti powders as Ti source by a tube furnace under argon atmosphere without preliminary dehydrogenation. 95 wt% pure Ti3AlC2 powders were synthesized from TiH2/1.1Al/2TiC at 1 450 °C for 120 min. High-purity Ti2AlC powders were also prepared from 3TiH2/1.5Al/C and 2TiH2/1.5Al/TiC powders at 1 400 °C for 120 min. The as-synthesized samples were porous and easy to be ground into powders. Sn or Si additives in starting materials increased the purity of synthesized Ti3AlC2 obviously and expanded the temperature range for the synthesis of Ti3AlC2. With Si or Sn as additives, high pure Ti3AlC2 was synthesized at 1 200 °C for 60 min from TiH2/x Si/Al/2TiC and TiH2/x Sn/Al/2TiC (x = 0.1, 0.2), respectively.