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In recent years, two-dimensional (2D) C-based materials have been intensively studied due to their excellent physicochemical properties.

We performed density functional theory calculations to investigate the electronic and magnetic properties of h-BN/MoS2 heterostructures intercalated with 3d transition-metal (TM) atoms, including V, Cr, Mn, Fe, Co, and Ni atoms. It was found that metal and magnetic semiconductor characteristics are induced in the h-BN/MoS2 heterostructures after intercalating TMs. In addition, the results demonstrate that h-BN sheets could promote charge transfer between the TMs and the heterogeneous structure. Specifically, the h-BN/MoS2 heterostructure transforms from an indirect semiconductor to a metal after intercalating V or Cr atoms in the interlayers. For Mn, Fe, and Co atoms, the bandgaps of the intercalated heterojunction systems become smaller when the spin polarization is 100% at the highest occupied molecular orbital level. However, the system intercalated with Ni atoms exhibits no spin polarization and non-magnetic character. Strong covalent-bonding interactions emerged between the intercalated TMs and the nearest S atom of the h-BN/MoS2 heterostructure. In addition, the magnetic moments of the TM atoms show a decreasing trend for all the interstitial intercalated heterostructures compared with their free-standing states. These results reveal that h-BN/MoS2 heterostructures with intercalated TMs are promising candidates for application in multifarious spintronic devices.

Photodetectors based on intrinsic graphene can operate over a broad wavelength range with ultrafast response, but their responsivity is much lower than commercial silicon photodiodes. The combination of graphene with two-dimensional (2D) semiconductors may enhance the light absorption, but there is still a cutoff wavelength originating from the bandgap of semiconductors. Here, we report a highly responsive broadband photodetector based on the heterostructure of graphene and transition metal carbides (TMCs, more specifically Mo2C). The graphene–Mo2C heterostructure enhanced light absorption over a broad wavelength range from ultraviolet to infrared. In addition, there is very small resistance for photoexcited carriers in both graphene and Mo2C. Consequently, photodetectors based on the graphene–Mo2C heterostructure deliver a very high responsivity from visible to infrared telecommunication wavelengths.

Photoelectric detectors based on binary transition metal chalcogenides have attracted widespread attention in recent years. However, due to the high-temperature synthesis of binary TMD, high-density deep-level defect states may be generated, leading to poor responsiveness or a long response time. Besides, the addition of an alloy will change the DLDSs from deep to shallow energy levels caused by S vacancies. In this paper, MoS2(1−x)Se2x nanostructures were synthesized by a hydrothermal method, and a novel type of photodetector was fabricated by using the synthesized material as a light sensitive material. The MoSSe-based photodetector not only has a high photocurrent, but also exhibits a wide spectral response in the range of 405 nm to 808 nm. At the same time, it can achieve a responsivity of 1.753 mA W−1 under 660 nm laser irradiation of 1.75 mW mm−2. Therefore, this work can be considered as a method of constructing a new type of photodetector with a simple process and low cost.

Flexible optoelectronic devices have been of great significance in recent years, owing to their extensive commercial and military applications. However, the manufacturing processes of most existing flexible photodetectors are particularly complicated and expensive. Employing a facile and low cost way for constructing a high performance flexible infrared photodetector is one of the effective strategies to facilitate its practical applications. Pencil-drawing is a popular method in novel electronic and optoelectronic devices, as it is a low cost and facile fabrication process. Herein, we report a novel flexible infrared photodetector using liquid-exfoliated Bi2Se3 nanosheets as a light sensitive material, pencil-drawn graphite as the electrodes, and paper as the substrate. The as-fabricated photodetector exhibits high photocurrent, excellent responsivity and long-term stability under 1064 nm infrared light irradiation. In addition, as the pencil-drawn photodetector is made of a flexible paper substrate, it also well exhibits stability and durability under bending conditions. This work is proposed to be a route to construct a novel flexible infrared photodetector with a facile manufacturing process and low cost.

We have studied the stable geometries, band structures and magnetic properties of transition-metal (V, Cr, Mn, Fe, Co and Ni) atoms absorbed on MoS2/h-BN heterostructure systems by first-principles calculations. By comparing the adsorption energies, we find that the adsorbed transition metal (TM) atoms prefer to stay on the top of Mo atoms. The results of the band structure without spin–orbit coupling (SOC) interaction indicate that the Cr-absorbed systems behave in a similar manner to metals, and the Co-absorbed system exhibits a half-metallic state. We also deduce that the V-, Mn-, Fe-absorbed systems are semiconductors with 100% spin polarization at the HOMO level. The Ni-absorbed system is a nonmagnetic semiconductor. In contrast, the Co-absorbed system exhibits metallic state, and the bandgap of V-absorbed system decreases slightly according to the SOC calculations. In addition, the magnetic moments of all the six TM atoms absorbed on the MoS2/h-BN heterostructure systems decrease when compared with those of their free-standing states.

It is highly desirable to develop highly-efficient anode materials for rechargeable lithium-ion batteries, which not only require large storage capacities, but also high stabilities and superior electrical conductivities. In this work, the electronic structures, stabilities, and the Li adsorption preferences of lithiated WS2 and NbSe2 monolayers as well as a lithiated WS2/NbSe2 heterostructure were systematically investigated using first principles calculations. It was found that compared with the metallic NbSe2 monolayer, the WS2/NbSe2 heterostructure appears to have a new state occupation where there was no state occupation in the sole NbSe2 monolayer. The metallic character ensures good electrical conductivity for lithium-ion batteries. Additionally, the diffusion barrier of the WS2/NbSe2 heterostructure is lower than that of WS2 and NbSe2 monolayers. A lower diffusion barrier guarantees better charge and discharge performances of the WS2/NbSe2 heterostructure as a battery electrode. Most importantly, the heterostructure was predicted to have quite a high theoretical specific capacity. Our results manifest that the WS2/NbSe2 heterostructure is a promising anode material, and provide valuable insights into the exploration of a rich variety of two dimensional heterostructure materials for next-generation flexible energy storage and conversion devices.

A single elemental hybrid composed of black phosphorus (BP) and red phosphorus (RP) is synthesized via a feasible sonochemical method. BP and RP can construct a new single elemental heterostructure. This kind of structure with an excellent interfacial contact between BP and RP would be beneficial to electron transfer and exhibits a superior electrochemical performance. Compared with the sole RP, the as-prepared BP/RP hybrid exhibits enhanced electrochemical performances as an electrode material for both lithium-ion batteries and supercapacitors. For lithium-ion battery applications, the BP/RP hybrid provides a high cycling performance with an initial discharge capacity of 2449 mA h g−1 and a reversible capacity of 491 mA h g−1 after 100 cycles. For supercapacitor applications, the specific capacitance of the BP/RP hybrid achieves a high value up to about 60.1 F g−1 and a long cycling life with a capacity retention of 83.3% after 2000 cycles. The present study demonstrates that the BP/RP hybrid has potential for application as an electrode with high performances in electrochemical energy-storage devices.

Recently, considerable efforts have been made to satisfy the future requirements of electrochemical energy storage using novel functional electrode materials. Binary transition metal oxides (BTMOs) possess multiple oxidation states that enable multiple redox reactions, showing higher supercapacitive properties than single component metal oxides. In this work, a facile hydrothermal method is provided for the synthesis of wall-like hierarchical metal oxide MMoO4 (M = Ni, Co) nanosheet arrays, which are directly grown on flexible carbon cloth for use as advanced binder-free electrodes for supercapacitors. By virtue of their intriguing structure, the resulted active material nanosheets with a high specific surface area can provide a large electroactive region, which could facilitate easy accession of electrolyte ions and fast charge transport, resulting in an enhanced electrochemical performance. Separately, the as-synthesized MMoO4 (M = Ni, Co) samples have exhibited superior specific capacitances (1483 F g(-1) of NiMoO4 and 452 F g(-1) of CoMoO4 at a current density of 2 A g(-1)), as well as excellent cycling stability (93.1% capacitance retention of NiMoO4 and 95.9% capacitance retention of CoMoO4 after 2000 cycles). The results show that the binder-free electrodes constructed by deposition of MMoO4 (M = Ni, Co) nanosheets on carbon cloth are promising candidates for the application of supercapacitors.

In this work, we demonstrate a simple hydrothermal synthesis of nickel sulfide/graphene nanosheets (Ni3S2/GNS) and use the nanocomposite as an electrode for a supercapacitor. X-ray diffraction, scanning electron microscopy and Raman spectroscopy were used to investigate the morphologies and microstructures of the resulting electrode materials. Detailed electrochemical characterization shows that the Ni3S2/GNS electrode exhibits high specific capacitance of about 1420 F g−1 at a current density of 2 A g−1. At a current density of 6 A g−1, the specific capacitance of the Ni3S2/GNS electrode remains fairly constant at the initial value over 2000 cycles, obviously illustrating a relatively high cycling stability. The outstanding electrochemical properties of the Ni3S2/GNS nanocomposite suggest that it has great potential for practical applications in high-performance supercapacitors.

By using a first-principles method within the framework of density functional theory, we study the formation energies of Cd and Ca dopants in Bi2Se3. The calculation results show that CdBi and CaBi are the most stable defects for Cd and Ca dopants in Bi2Se3, respectively. Additionally, both the CdBi and CaBi defects in Bi2Se3 are p-type dopants, with accepter levels at e(0/−1) = 0.030 eV and e(0/−1) = 0.028 eV, respectively. Comparing their formation energies with that of the native defects under a different growth condition, CdBi and CaBi can effectively compensate the n-type native defects, VSe and SeBi, under Se-rich growth conditions. It is interesting to note that such compensation effects become weaker, gradually, with the growth conditions changing from Se-rich to Bi-rich. Therefore, a p-to-n or n-to-p type conversion for Bi2Se3 can be achieved by changing the growth conditions. Simultaneously, the Fermi level, which is determined by the charge neutrality condition, can be effectively tuned, which is in agreement with previous experimental reports.

A binder-free electrode is prepared by directly depositing electrochemically reduced graphene oxide (ERGO) on the metal current collector. Fourier transform infrared spectroscopy and Raman spectrum have been used to demonstrate the effective reduction of graphene oxide on the electrode, and the porous structure of the ERGO film was further characterized by scanning electron microscopy. The electrochemical properties of ERGO were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). Electrochemical measurements showed that the binder-free ERGO electrode had high specific capacity, good cycle stability, as well as excellent high-rate capability. The specific capacitance of the constructed electrode was 131.6 F g−1 at a scan rate of 10 mV s−1 and maintained 66.9% of the initial value when the scan rate was increased up to 1000 mV s−1. Owing to its favorable electrochemical performance, this binder-free ERGO electrode with porous structure has great potential in future commercial electrochemical supercapacitors.

We have carried out first-principles calculations and theoretical analysis to explore the structural, spin-polarized electronic and magnetic properties of bi-layered MoS2 with transition-metal (TM) atoms (Cr, Mn, Fe, Co and Ni) doped in the interlayer. The charge density distribution indicates that the doping TM atoms and the nearest S atoms in the lower and upper planes display a clear covalent-bonding feature. The local moments of the doping TM atoms are smaller than the magnetic moments of their free states. Also, the spin polarization is found to be 100% at the Fermi level or HOMO level for interlayer doping with Cr, Mn, Fe and Co.

An anatase TiO2 nanosheet with discrete integrated subunits was successfully synthesized via a rapid annealing treatment, which could be classified as non-equilibrium conditions on an as-prepared hydrogen titanate nanosheet. This unique TiO2 nano-object is uniform in length and width as a “sheet-like” shape which is integrated with numerous discrete nanocrystalline subunits. In contrast with the internal architecture of the TiO2 nanosheets produced under equilibrium and non-equilibrium conditions, the local structure collapse transformation mechanism from the hydrogen titanate nanosheet to the anatase TiO2 nanosheet with internal architecture is discussed. This unique anatase nano-object electrode exhibits high reversible lithium ion storage capacities and superior cyclic capacity retention at a high current rate. Such enhanced lithium storage performance could be attributed to the discrete subunits aggregation allowing efficient Li+ ion diffusion and the interior anisotropy in the nanosheet can be more effective to buffer the volume variation during the lithium insertion/desertion cycle.

Herein, a new nanocomposite consisting of up-conversion (UC) material (YF3:Yb3+,Tm3+), TiO2 (P25) and graphene (GR) has been prepared and shown to be an advanced sunlight activated photocatalyst. During the facile hydrothermal method, the reduction of graphene oxide and loading of YF3:Yb3+,Tm3+ and P25 were achieved simultaneously, and the functionalities of each part were integrated together. The as-prepared ternary UC–P25–GR nanocomposite photocatalyst exhibited great adsorptivity of dyes, a significantly extended light absorption range, efficient charge separation properties and superior durability. Indeed, the photocatalytic activity of this novel ternary nanocomposite under sunlight was improved compared with those of P25–GR nanocomposites and bare P25. Overall, this work could provide new insights into the fabrication of ternary composites as high performance photocatalysts and facilitate their application in environmental protection issues.

A convenient hydrothermal intercalation/exfoliation method for large-scale manufacturing of bismuth telluride (Bi2Te3) nanosheets is reported here. Lithium cations can be intercalated between the layers of Bi2Te3 using the reducing power of ethylene glycol in the common hydrothermal process, and high quality Bi2Te3 nanosheets with thickness down to only 3–4 nm are obtained by removing lithium in the following exfoliating process. Scanning electron microscopy, transmission electron microscopy and Raman spectrum characterizations confirm that the high yield of Bi2Te3 nanosheets with good quality were successfully achieved and the sizes of the immense nanosheets reached 200 nm width and 1 μm length. This hydrothermal intercalation/exfoliation method is general, as it has been extended to other layered materials, such as Bi2Se3 and MoS2. Our results suggest a simple route for the large-scale production of thin and flat Bi2Te3 nanosheets, which may be beneficial to further electronic and spintronics applications.