Microwave absorbers with layered structures that can provide abundant interfaces are highly desirable for enhancing electromagnetic absorbing capability and decreasing the thickness. The atomically thin layers of two-dimensional (2D) transition-metal carbides (MXenes) make them a convenient precursor for synthesis of other 2D and layered structures. Here, laminated carbon/TiO hybrid materials composed of well-aligned 2D carbon sheets with embedded TiO nanoparticles were synthesized and showed excellent microwave absorption. Disordered 2D carbon layers with an unusual structure were obtained by annealing multilayer TiC MXene in a CO atmosphere. The minimum reflection coefficient of laminated carbon/TiO composites reaches -36 dB, and the effective absorption bandwidth ranges from 3.6 to 18 GHz with the tunable thickness from 1.7 to 5 mm. The effective absorption bandwidth covers the whole Ku band (12.4-18 GHz) when the thickness of carbon/TiO/paraffin composite is 1.7 mm. This study is expected to pave the way to the synthesis of carbon-supported absorbing materials using a large family of 2D carbides.

Recent progress in 3D printing of electrochemical energy storage devices.

Nonprecious metal catalysts for hydrogen evolution reaction (HER) have recently received growing attention. Herein, we designed a highly active MXene nanofiber catalyst with a high specific surface area (SSA) via the hydrolyzation of bulk MAX ceramics, and a subsequent HF etching process. Compared with traditional MXene flakes, the MXene nanofibers delivered a much higher SSA and exposed more active sites in the cross section. As a result, the MXene nanofiber delivered an enhanced HER activity with a low overpotential of 169 mV at a current density of 10 mA cm–2, a depressed Tafel slope of 97 mV dec–1, and low electrochemical resistance. The improved SSA and exposed active sites are responsible for the enhanced activity. This work provides a novel synthesis method for MXene nanofibers, and MXene nanofibers are also promising for applications in batteries, supercapacitors, and catalytic fields.

Using the linear response theory, the vibrational and dielectric properties are calculated for c-BN, w-BN and h-BN. Calculations of the zone-center optical-mode frequencies (including LO-TO splittings) are reported. All optic modes are identified and agreement of theory with experiment is excellent. The static dielectric tensor is decomposed into contributions arising from individual infrared-active phonon modes. It is found that all of the structures have a smaller lattice dielectric constant than that of electronic contribution. Finally, the infrared reflectance spectrums are presented. Our theoretical results indicate that w-BN shows a similar reflectivity spectrum as c-BN. It is difficult to tell the wurtzite structure from the zinc blende phase by IR spectroscopy.

TiO2 is a promising photocatalytic material for hydrogen generation. However, the fast recombination of electron–holes restricts the photocatalytic performance of TiO2. Herein, this study demonstrates a 2D‐layered carbon/TiO2 (C/TiO2) architecture via CO2 oxidation of 2D‐Ti3C2, in which the 2D carbon layers provide electron transport channels and improve the hole–electron separation efficiency. Compared to Ti3C2 support, the thickness of derived carbon supports is significantly reduced, which enhances the light intensity arriving at the surface of TiO2. The oxidation parameters are investigated systematically. It is found that high temperature and high CO2 gas flux lead to the formation of crystal TiO2 and the oxidation of carbon layers. The bandgap of 2D‐layered C/TiO2 samples is ranged from 2.83 to 2.89 eV. The 2D‐layered C/TiO2 delivers enhanced photocatalytic activity compared with pure TiO2 catalysts. The optimal photocatalytic hydrogen evolution rate of 2D‐layered C/TiO2 is up to 24.04 µmol h−1, which is about 89 times higher than that of pure TiO2. This research broadens the applications of C/TiO2 hybrids and provides new approach to synthesize novel 2D‐layered materials for photocatalytic applications.

TiO2 is an ideal photocatalyst candidate except for its large bandgap and fast charge recombination. A novel laminated junction composed of defect‐controlled and sulfur‐doped TiO2 with carbon substrate (LDC‐S‐TiO2/C) is synthesized using the 2D transition metal carbides (MXenes) as a template to enhance light absorption and improve charge separation. The prepared LDC‐S‐TiO2/C catalyst delivers a high photocatalytic H2 evolution rate of 333 µmol g−1 h−1 with a high apparent quantum yield of 7.36% at 400 nm and it is also active even at 600 nm, resulting into a 48 time activity compared with L‐TiO2/C under visible light irradiation. Further theoretical modeling calculation indicates that such novel approach also reduces activation energy of hydrogen production apart from broadening the absorption wavelength, facilitating charge separation, and creating a large surface area substrate. This synergic effect can also be applied to other photocatalysts' modification. The study provides a novel approach for synthesis defective metal oxides based hybrids and broaden the applications of MXene family.

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Nonoxides have been widely employed as highly efficient catalysts for water splitting. However, these nonoxides suffer from obvious surface transformation and poor structural stability, which must be urgently remedied. Herein, the interfacial engineering of Co4N via mesoporous nitrogen-doped carbon (NC) was first carried out, in which NC can significantly suppress the oxidization of Co4N in alkaline media, ensuring the efficient interfacial charge transport between Co4N and NC. As a result, extremely low overpotentials @10 mA cm–2 of 62 mV (hydrogen evolution reaction, HER) and 257 mV (oxygen evolution reaction, OER) and small Tafel slopes of 37 mV (HER) and 58 mV dec–1 (OER) were achieved in alkaline media. Theoretical calculations suggest that their synergetic coupling effects can significantly facilitate the charge-transfer process and further greatly reduce the energy barrier for water splitting. This work underscores the importance of the surface engineering of nonoxides and efficient approaches for the design of stable catalysts for electrocatalysis.