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Local strain, as a small degree and single direction strain method, can effectively regulate the structures and electronic properties of armchair Janus MoSSe nanoribbon, so that the system can be transformed from the original 0.467 eV indirect band gap into 0.259 eV (3-zig), 0.117 eV (3-arm), 0.080 eV (6-arm) and 0.139 eV (9-zig) direct band gap semiconductor according to the different strain degrees and directions. Compared with traditional MoS2 and MoSe2 nanoribbons, Janus MoSSe nanoribbon shows relatively stable band structure under local strain. The structures and electronic properties of Janus MoSSe nanoribbon are anisotropic when the local strain along different directions. Due to the broken mirror symmetry of Janus system and the appearance of in-plane local polarization, the spin polarization effect of Janus nanoribbon under local strain is more remarkable. When the local strain degree C = 0.167 along the zigzag direction and the local strain C ≥ 0.056 along the armchair direction, the Janus nanoribbon exhibits half-metallic property and surprisingly induces magnetic moment. For the local strain along the direction of armchair, the total magnetic moment of the system can be up to 2.05 μB when C = 0.111. To sum up, a local strain method is applied to the nanoribbon system, which can effectively regulate the geometric configuration and electronic structure without external doping, and introduce magnetism, providing the possibility for expanding nanoribbons as potential nanoelectronics and spintronic material.

Electrocatalytic hydrogen evolution is an exercisable way to achieve large-scale application of hydrogen energy. It is of great significance to develop an effect, stable, and cost-effective electrocatalyst. Here, we applied the two-dimensional (2D) bismuth (Bi) to the electrocatalytic hydrogen evolution, and proposed the strategies to enhance the catalytic performance of the catalyst. Due to more active sites located along the edges of 2D structure, Bi nanosheets revealed a higher electrocatalytic activity (overpotential of −958 mV vs RHE at 10 mA cm−2, Tafel slope of 122 mV/dec) than the bulk counterpart. To further evaluate the electrocatalytic performance of Bi nanosheets, the typical parameters measured in different H+ concentration (C[H+]) are carried out. The improved catalytic activity obtained in 0.5 M H2SO4 is attributed to enhancing the hydrogen adsorption and accelerating the charge transport on the surface of catalyst. Moreover, the durability of Bi nanosheets has been texted, where the current is not evident fluctuation during the 40,000 s electrolysis measurement indicating its excellent stability. The present work expands the application of Bi in the catalysis and provides the simple strategies to improve its hydrogen evolution performance.

Germanium selenide attracts emerging attention for applications in high-performance field-effect transistors and photodetector, due to its unique photoelectric performances and tunable bandgap. Herein, the germanium selenide-reduced graphene oxide (GeSe-RGO) hybrid is successfully synthesized by loading liquid-phase exfoliated GeSe nanosheets on the 2D graphene via a hydrothermal reduction process. It is demonstrated that the photoresponse performance of the photoelectrochemical (PEC) device constructed by the synthesized GeSe-RGO hybrid is significantly enhanced in comparison to the one built by the sole GeSe nanosheets. The results of the PEC tests display the photocurrent density can reach to 8.45 μA/cm2 at the bias of 0.8 V, which is approximately 4 times that of sole GeSe nanosheets. Meanwhile, with the increase of illumination intensity, the photocurrent density of the GeSe-RGO photodetector almost presents a linear increase. When the illumination intensity is 90 mW/cm2, the photoresponsivity value is up to 116 μA/W. In addition, the GeSe-RGO hybrid shows a durable photoresponse capability under the bias of 0 V, revealing that such a hybrid has the excellent self-powered ability in the PEC system. There is no evident degradation on the photoresponsive performance of GeSe-RGO photodetector after 50 light on-off cycling, indicating the good stability of the hybrids. The enhanced performance of the GeSe-RGO hybrid is attributed to the outstanding photoresponsive capability of RGO and the effective separation of photo-generated electron-hole pairs. Our work indicates that the GeSe-RGO hybrid has great prospects for future applications in PEC-type photodetector devices.

Two-dimensional (2D) molybdenum disulfide (MoS2) nanomaterials have emerged as promising candidates for constructing excellent supercapacitors, but the lack of large-scale, efficient and low-cost methods for preparing MoS2 nanosheets severely hinders its practical application. This study demonstrates an accessible and efficient approach for electrochemical exfoliating bulk MoS2 into high-quality MoS2 nanosheets with size distribution in the range of 1–3 μm and a thickness of several nanometers in an easily available inorganic salt solution. Furthermore, we construct symmetric all-solid-state supercapacitors based on exfoliated MoS2 nanosheets. The 2D structure will provide stable channels to facilitate the intercalation/desorption of ions during charge and discharge, and to a certain extent can prevent deposition and agglomeration. Therefore, compared with the unexfoliated MoS2, as-prepared MoS2 nanosheets show great improvement in supercapacitor performance (the specific capacitance increases from the original 130 F g−1 to 215 F g−1 at 5 A g−1, for instance). In detail, the electrode possesses a specific capacitance of 285 F g−1 at a current density of 2 A g−1 and maintains the great capacitance retention of 83.8% at 8 A g−1. Moreover, the supercapacitor exhibits a high energy density of 136.8 Wh kg−1 at a power density of 2550 Wh kg−1. This work provides basic research on the preparation of 2D nanomaterials by electrochemical exfoliation.

Two-dimensional (2D) MoTe2 nanomaterials have emerged as a promising candidate for constructing excellent supercapacitors due to their high capacitive performance. Recent studies have revealed that MoTe2 has broad prospects as an active material in supercapacitors, although its strict requirements in terms of the external environment and complex preparation process remain serious obstacles to its practical application. Toward this end, MoTe2 nanosheets (NSs) were prepared by a facile and inexpensive liquid-phase exfoliation approach for the fabrication of MoTe2 electrodes. The results show that the MoTe2 NSs exhibit significantly improved electrochemical performance, with a specific capacitance (859 F g−1) more than three times that of bulk MoTe2 (271 F g−1) at a current density of 1 A g−1. In addition, the MoTe2-based electrode showed excellent cycle stability and maintained excellent specific capacitance (92.7% of the initial value) after 1000 cycles under the working condition of a current density of 10 A g−1. This study describes a fundamental investigation on the energy storage and conversion properties of 2D layered materials.

Van der Waals (vdW) heterostructure, vertically assembled by two kinds of two-dimensional layered materials with extraordinary electronic and optical properties, has emerged as an interesting candidate in the applications of electronics and optoelectronics. It is known that vacancies are crucial in determining the physical properties of materials, and always exist in the materials during the process of actual experimental preparations and can be artificially introduced. In the present work, the structures and electronic properties of a black phosphorus/molybdenum disulfide (BP/MoS2) vdW heterostructure with P atom vacancies are investigated via first principles calculations. Based on the structural symmetry, two types of heterostructures with single-atom vacancy and three types of heterostructures with diatomic vacancies are constructed. It is found that the presence of a single P atom vacancy leads to the transformation from semiconductor to metal in the BP/MoS2 heterostructure, which is mainly due to the contribution of the remaining P atomic p orbitals based on analyses of the partial density of states (PDOS). On the other hand, the heterostructures with diatomic P atom vacancies still maintain their pristine semiconductor features, along with a decrease in their bandgap value. In addition, the plane electrostatic potential indicates that the introduction of P atom vacancy defects causes a change in the electrostatic potential of the BP atomic layer, resulting in asymmetric electrostatic potential on both sides of the BP layer. Finally, it is interesting to note that the accumulation-depletion of electrons occurs around the vacancy, but also partially emerges at the MoS2 layer. Our results provide the possibility for the application of 2D-vacancy-defect heterostructure systems.

Inspired by potential application prospects of spintronics and valleytronics, a novel heterobilayer Janus structure is designed by replacing the chalcogenide atomic layers in the original bilayer MoS2. Based on first-principles calculations, it is found that the SMoS/SeMoS structure exhibits a direct band-gap semiconductor and a typical type-II band alignment with longer carrier lifetime. The transition metal (TM) atom represented by V/Cr/Mn can be stably adsorbed on the heterobilayer Janus SMoS/SeMoS sheet and effectively introduce magnetic moments (m). The calculation results demonstrate that the most stable adsorption site of the TM atom is CX(A), and the TM (V/Cr/Mn) adatom modified SMoS/SeMoS system is converted into metal (V-) or half-metal (Cr/Mn-), respectively. Under the coupling of different indirect exchange interactions, the structure exhibits stable intrinsic anti-ferromagnetic interactions for V-SMoS/SeMoS and ferromagnetic ground state for Cr/Mn-SMoS/SeMoS, respectively, and the magnetic transition temperature (T c) reaches a high temperature or even room temperature. Moreover, the robust out-of-plane magnetocrystalline anisotropy energy ensures stable long-range magnetic order. Specifically, the combination of spin injection and strong spin–orbit coupling interaction effectively breaks the time-reversal symmetry, which leads to valley polarization of the system. Based on this, the biaxial strain can effectively regulate the electronic structure, magnetic properties and valley polarization of TM-SMoS/SeMoS nanosheets with double breaking of spatial-inversion and time-reversal symmetry.

In this report, WS2-reduced graphene oxide (WS2-rGO) hybrid was successfully synthesized through a hydrothermal reduction process in which WS2 nanosheets (WS2 NSs) were prepared by a lithium-ion intercalation and exfoliation technique. The photodetection properties of as-synthesized samples have been systematically investigated using a photoelectrochemical (PEC) system, which presents a reproducible photoresponse of WS2-rGO under zero bias, indicating that such hybrid is a promising photoanode for self-powered photodetectors. At a bias of 0.8 V, the photocurrent density of WS2-rGO hybrid was 4.32 μA/cm2, which is approximately 800% of that of the bare WS2 photodetector. Meanwhile, the photoresponsivity of as-prepared WS2-rGO hybrid increases linearly with the irradiation intensity, up to 9.3 μA/W at power density of 30 mW/cm2. In addition, the stability test exhibits no conspicuous degradation after 100 cycles. The enhanced performance of the WS2-rGO hybrid benefits from the high carrier mobility of rGO and the efficient separation of photogenerated carriers at the WS2-rGO interface. This research demonstrates that the WS2-rGO hybrid has a good prospect in PEC-type photodetectors.

Tin disulfide/graphene composites were successfully synthesized by one-step hydrothermal method. A novel SnS2/graphene solid-state photoelectrochemical photodetector with the advantages of small size, light weight, easy portability, and easy storage was successfully constructed based on solid-state electrolytes. The SnS2/graphene composites with pleated flower-like structure were characterized by scanning electron microscope characterization. At the same time, X-ray diffraction and Raman spectroscopy were carried out to confirm the composition and inherent physical properties of SnS2/graphene. Photoelectrochemical tests show that the SnS2/graphene solid-state photoelectrochemical photodetector has excellent photoresponse characteristics, and its photocurrent density is about 9 nA/cm2 under sunlight irradiation without additional power. In addition, the SnS2/graphene solid-state photoelectrochemical photodetector exhibits a good stability and the photocurrent density is only slightly attenuated (77% of the initial value) after 2000 s (50 cycles). Experimental results that SnS2/graphene solid-state photoelectrochemical photodetector is a potential new type self-powered photodetector. We believe that solid-state electrolytes with the advantages of small size, light weight, easy portability, and easy storage can be extended to other fields, such as solar cells, and supercapacitors.

Molybdenum Telluride (MoTe2) is widely used in the field of optoelectronics because of its excellent electron mobility and good environmental stability. Recent advances have shown that the reduction in the thickness of two-dimensional (2D) layered materials allows for greater surface area and more active sites to enhance electrocatalytic performance. Here, we prepared MoTe2 nanosheets by liquid exfoliation. Characterization of the morphology and lattice structure of MoTe2 nanosheets by a series of characterization methods. A three-electrode electrochemical system test results demonstrated that the MoTe2 nanosheets have excellent electrocatalytic activity and stability in H2SO4 solution compared to bulk MoTe2. In addition, the MoTe2 nanosheets also exhibited optimal electrocatalytic properties for hydrogen evolution reaction (HER) with −309 mV overpotential at a current density of 10 mA/cm2 and a low Tafel slope of 118.9 mV/dec in a 0.5 mol/L (M) H2SO4 solution. Our work demonstrates that MoTe2 nanosheets have good prospects for use in electrocatalytic devices as high-performance electrocatalysts.

Tin disulfide (SnS2) has been attracted intensive attention in the field of photoelectric conversion due to its appropriate band gap and glorious electronic mobility. The hexagon SnS2 nanosheets has been successfully integrated through a facile one-pot hydrothermal method. SEM images, Raman spectra, atomic force microscope and X-ray diffraction patterns are measured to carry out to investigate the morphologies and microstructures of SnS2 nanosheetsm, confirming a good crystallized SnS2. Then, the photochemical activity of as-prepared SnS2 nanosheets were tested in the electrolyte of Na2SO4. Photoelectrochemical tests demonstrate that the photocurrent density of as-prepared hexagon SnS2 nanosheets (1.66 µA/cm2 at a light intensity of 140 mW/cm2) is hugely increased with increasing light intensity. Furthermore, after 50 cycles, the photocurrent density does not change significantly, indicating that the as-prepared SnS2 nanosheets possesses superior stabilities. The outstanding photocatalytic performances of SnS2 nanosheets are not only resulted from its huge specific surface area, which can harvest more light and provide more active sites, but also attributed to its superior charge mobility, which can facilitate the separation photogenerated electron–hole pairs and the charge transfer between SnS2 nanosheets and the electrode. The most important is that our work reveals the hexagonal SnS2 nanosheets not only possess superior photoelectrochemical properties, but also have great potential applications in energy conversion and photodetector fields.

Hybridization of WS 2 and TiO 2 by a facile hydrothermal method was realized to construct WS 2 - TiO 2 heterostructure photodetector which exhibits preferable photoresponse activity in association with structural robustness. The relationship between photocurrent density and applied bias potential has also been uncovered. Photoresponse measurements demonstrate the photocurrent density of WS 2 - TiO 2 hybrid nanosheets (HNs) has been greatly improved when compared to that of as-prepared TiO 2 , while the steady current density can achieve 130 nA ∕ cm 2 when applied potential is 1.0 V. Besides that, the stability test exhibits no detectable distinction after processing 15 cycles. The improved photoresponse activities can be attributed into the positive synergetic effect between the WS 2 and TiO 2 . We hope the present work can provide fundamental implementations about WS 2 - TiO 2 heterostructure photodetector, meanwhile, offering it potential availabilities for constructing high-performance photodetectors.

The exploration of high performance supercapacitors has received emerging the worldwide research interests in satisfying the gradually increased energy consumption. In this paper, we adopt a facile hydrothermal strategy to synthesize ternary FeCo2O4 directly on nickel foam. A series of structure such as nanowires, nanoflake@nanowire hetero-structure and hierarchical nanospheres have been achieved via modulating the synthetic time. The morphology and structure of the as-prepared samples are characterized by using scanning electron microscopy and X-ray diffraction spectroscopy. The relationship between the detail processing parameters and electrochemical performance are also revealed by cyclic voltammetry, galvanostatic charge-discharge measurements, cycle stability tests and electrochemical impedance spectroscopy. Notably, the as-prepared nanoflake@nanowire hetero-structure exhibits a high specific capacitance of about 969 F g−1 at 2 A g−1 in alkaline aqueous solution and a remarkable cycling stability (91% capacity retention after 2000 cycles). The excellent supercapacitors performance of nanoflake@nanowire hetero-structure can be attributed to the high conductivity, large active area as well as robust architectures that derive from structural synergetic effects. Furthermore, a symmetric all solid-state supercapacitor has been fabricated by using nanoflake@nanowire hetero-structure as both the anode and cathode electrodes. The as-fabricated supercapacitor delivers excellent electrochemical performance. It's anticipated that FeCo2O4 would be a promising material for electrochemical energy storage applications.

A novel P25/Black phosphorus/Graphene hybrid has been successfully prepared by loading two components [P25 and Black phosphorus (BP)] on graphene nanosheets via a simple one-step hydrothermal method. The P25/BP/Graphene hybrids are characterized by scanning electron microscopy (SEM),Raman spectra and X-ray diffraction patterns, which confirm a good crystallized P25 and BP hybridization with graphene. Photoelectrochemical tests verify that the photocurrent density of as-prepared P25/BP/Graphene ternary hybrid (9.32 μA/cm2) is greatly improved at 1 V, which is nearly 34 times higher than that of sole P25 and 4.8 times as much as that of P25/Graphene. The improved photocatalytic activity is proposed to be benefited from the higher carrier mobility and additional accessible sites derive from the special configurations of ternary hybrid, as well as the introduction of the visible and near-infrared-activated BP photocatalyst. More importantly, this work demonstrates that the as-prepared P25/BP/Graphene hybrid would be an attractive candidate as high-performance photocatalyst, and provide positive proof of concept for developing the practical applications of graphene and black phosphorus based composites.

Bismuth as an element of group VA (P, As, Sb, Bi), which is considered as beyond graphene materials, has attracted much attention because of its stable topological insulator properties. Herein, photoelectrochemical (PEC)-type photodetector based on two-dimensional bismuth nanosheets was designed and fabricated. By using a solid electrolyte to replace the traditional electrolyte, we have achieved a novel structure to make the device more portable. Besides that, due to the solid/liquid heterojunction, which generates an built-in electric field that can separate electron hole pairs effectively, this type of photodetector possess self-powered ability, and it exhibited preferable photoresponsivity which is about 0.5 μA W−1 without external bias potential; meanwhile, the rise time of the photodetector is about 3.3 s and decay time is about 1.8 s. Moreover, we used the flexible indium-tin oxide (ITO) as the substrate; the prepared device can work under the bending states. The novel structure and the excellent properties of the fabricated self-powered flexible PEC-type photodetector make it more promising in the optical detection field.

Metal atom adsorption is recently considered to be an efficient approach to achieve stability of black phosphorus required by practical devices with no damage to its pristine excellent properties. Using first-principles calculations, we studied the structures and electronic properties of monolayer black phosphorus with Fe atom adsorption under different biaxial strain. Monolayer BP becomes an indirect bandgap semiconductor due to the contribution of adsorbed Fe atom. Strain is considered as a promising way to turn the electronic structures of the adsorption systems. The compressive strain reduces the band gap value of the systems, and eventually results in a semiconductor-metal transition when the strain reaches −8%. The tensile strain would turn the value of band gap ranging from 0.96 eV to 0.60 eV, and an indirect-direct band gap transition would occur with the tensile strain of 4%. In addition, it is found that the charge density difference and charge transfer nearly unchanged under different strain, means that the Fe–P covalent bonds are very strong. The combination of adjustable electronic properties with stability makes black phosphorus an attractive material for fundamental physics studies.

Antimony phosphorus in the alpha phase (α-SbP) is a novel two-dimensional binary material with suitable band gap and environmental stability, it has attracted attention for its promising applications in the field of optoelectronics. In this work, the electronic and optical properties of α-SbP monolayer under biaxial strain have been studied by first principles calculation method based on density functional theory. It is found that when the tensile strain is applied, the band gap value of monolayer SbP increases firstly and then decreases under tensile strain, but the whole band gap value fluctuated is controlled within 0.08 eV. However, in the process of applying compressive strain, the band gap value decreases linearly with the strain value, and semiconductor-metal transition occurs at about −5% strain value. This is due to the difference in coupling between Sb and P atoms. Its optical properties under different strains are analyzed in detail, and it is found that the optical properties of SbP changed little under tensile strain, the light absorption peak is mainly concentrated in the ultraviolet region. In contrast, the compressive strain significantly adjust the optical properties of SbP. The innovation of this work is that the optoelectronic properties of SbP are studied by means of biaxial strain regulation. We find that the optoelectronic properties of SbP are robust to tensile strain. On the other hand, compressive strain has a significant effect on the photoelectric properties of SbP, and semiconductor-metal phase transition occurs. The research work in this paper provides theoretical support for the applications of monolayer α-SbP as a robust tensile and flexible compression material in optoelectronic nanodevices.

Designing a Z-scheme heterojunction is of great significance to achieve high separation of photogenerated carriers and strong photo-redox properties of two semiconductor materials. In photosynthesis, the effects of photocatalytic electrolytes (adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH)) on chemical energy has attracted numerous interests. In this case, developing photocatalytic electrolytes with more active site and efficient charge extraction and separation would be beneficial for superior photocatalytic activity in Z-scheme system. Herein, we synthesized a Black/Red (BP/RP) phosphorus Z-scheme hybrid via a feasible two-steps sonochemical method, and the adding photocatalytic electrolytes ATP and NADPH in KOH solution endow the system with new vitality in photocatalysis. Consequently, photoelectrochemical (PEC) tests demonstrated the as-prepared BP/RP Z-scheme hybrid exhibits enhanced photocurrent of 9 μA/cm2 at 0.5 V compared to the sole RP, while adding NADPH and ATP, the photocurrent of BP/RP Z-scheme hybrid shows dramatic increment of 30 μA cm−2 at a bias potential of 0.6 V. The improved photocatalytic activity is ascribed to the abundant active sites, higher carrier mobility of the BP/RP Z-scheme system, as well as the efficient photogenerated carrier separation and the prolonged lifetime of photocatalytic electrolytes. This work demonstrated the photocatalytic electrolytes can meet the unity of coordination and efficiency of achieving efficient PEC catalytic in the Z-Scheme system, and provides positive ideas for the possibility and superiority for other 2D materials in the field of ultrafast Photonics, photodetectors, etc.

A flexible Bi 2 Se 3 /Graphene (BSG) composite paper has been prepared through a simple vacuum filtration method and a thermal reduction together. The BSG composite paper was directly used as anode electrode for lithium-ion batteries, without using any polymer binders or conduction additives. In contrast to the pure Bi 2 Se 3 , the BSG exhibits high reversible lithium ion storage capacities and superior cyclic capacity retention. It proposed that the superior lithium storage performances would be attributed to the special construction of the as-prepared BSG paper, in which the graphene can not only act as conductive network for electrodes, but also act as a frame to alleviate volume expansion or aggregation of Bi 2 Se 3 nanosheets during lithiation/delithiation. The as-prepared BSG paper shows a great potential as an anode materials for flexible Li-ion batteries.

In this work, CuO nanoneedles have been in situ grown on Cu foam through simple thermal oxidation in the air. The morphologies and microstructures of as-prepared sample were characterized by using X-ray diffraction, Raman spectrum, scanning electron microscopy, transmission electron microscopes. It was found that the one-dimensional CuO nanoneedles with single crystalline were uniform distributed upon the layer of Cu foam’s skeleton. Directly using the as-prepared sample as the anode material for lithium-ion battery, the electrochemical performances of CuO nanoneedles on Cu foam were investigated by galvanostatic discharge–charge tests, cyclic voltammetry, as well as impedance spectroscopy measurement. The in situ growth electrode without binder realized an initial capacity as high as 940 and 446 mAh g−1 still retained even after 100 cycles of charging and discharging. The superior lithium storage performance may be attributed to the unique hierarchical architectured of nanoneedles on skeleton of porous foam, which offers excellent electro-conductivity for the intimate contact between CuO active material and Cu foam current collector, and provides a large surface to volume ratio that favors lithium-storage. The results propose that the as-prepared CuO nanoneedles on Cu foam would be a potential anode material for lithium-ion battery applications.

Novel TiO2/MoSe2 catalyst has been synthesized via a hydrothermal method. The morphologies, microstructures and optical properties were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, UV–Vis absorption spectroscopy, the result show that a large quantity of MoSe2 nanosheets (NSs) were obtained from MoSe2 bulks by lithium intercalatation way and TiO2 nanoparticles has been grown on the NSs successfully. According to the photoelectrochemical measurements, the TiO2/MoSe2 hybrid nanostructures show the photocurrent density of 15 μA/cm2, which is much higher than bare TiO2 of 8 μA/cm2 and bare MoSe2 of 10 μA/cm2. It is proposed that type-II heteroshtucture of TiO2/MoSe2 can efficiently promote photocatalytic activity.

Two-dimensional NiSe2 nanosheets arrange on three-dimensional carbon cloths (CC) have been synthesized through a facile two-step hydrothermal process. The as-prepared NiSe2/CC photoelectrode demonstrates outstanding photoelectrochamical (PEC) performance. Subsequently, a series of characterization techniques including X-ray diffraction and Raman spectra are carried out and confirm a well crystalline NiSe2/CC. Additional morphological and microstructural tests depict large-scale NiSe2 nanosheets are uniformly aligned on the basement of conductive carbon cloth. The PEC measurements show the steady photocurrent density can be effectively raised from 10 to 600 μA/cm2 when bias potential increases from 0 to 0.5 V, which is proposed to be attributed to the adequate exposure of active sites and reduction of surface contact resistance provided by carbon cloth. The structure and performances of hydrothermal synthesized NiSe2/CC suggest promising applications in the field of PEC hydrogen production.

We demonstrated that titanium dioxide (TiO2) significantly enhances the reversible capacity of silicon nanoparticles (SiNPs) used as the anode material for lithium ion batteries. The novel silicon and titanium dioxide core–shell nanoparticles (Si/TiO2) was prepared via a facile sol–gel method with the following heat-treatment process. The as-prepared materials were confirmed by X-ray diffraction, Raman spectra and transmission electron microscope. As an anode material for battery, the electrode was investigated by a series of electrochemical measurements. The as-prepared Si/TiO2 electrode exhibits superior electrochemical performance in comparison with pure SiNPs, which realizes an initial capacity as high as 2636.9 mAh/g and still retains 1010.7 mAh/g even after 100 cycles of charging and discharging. The excellent cycle stability and capacity retention of the as-prepared electrode would be attributed to the existence of TiO2 layers to accommodate the large volume changes of silicon and enhancement ability to minimizes loss of pulverization during the lithium insertion/desertion cycles. Therefore, the as-prepared Si/TiO2 is believed to be an potential anode material for lithium-ion battery applications.

In this work, SnS 2 nanoplates entrapped graphene aerogel has been successfully prepared by simple self-assembly of reduced graphene oxide obtained through mild chemical reduction. Structural and morphological investigations demonstrated that SnS 2 nanoplates are highly dispersed in the three dimensional (3D) porous graphene matrix. When served as anode material for lithium-ion batteries, the electrochemical properties of SnS 2 /graphene aerogel (SnS 2 /GA) were evaluated by galvanostatic discharge–charge tests, cyclic voltammetry and impedance spectroscopy measurement. Compared with pristine SnS 2 , the SnS 2 /GA nanocomposite achieved a much higher initial reversible capacity (1186 mAh g −1 ), superior cyclic stability (1004 mAh g −1 after 60 cycles, corresponding to 84.7% of the initial reversible capacity), as well as better rate capability (650 mAh g −1 at a current density of 1000 mA g −1 ). This significantly improved lithium storage performance can be attributed to the good integration of SnS 2 nanoplates with 3D porous graphene network, which can not only provide much more active sites and easy access for Li ions intercalation, but also prevent the aggregation of SnS 2 nanoplates and facilitate fast transportation of Li ions and surface electrons during the electrochemical process.

Here, novel graphene/TiO 2 nanocomposite has been successfully prepared by loading flocculent-like titanate nanostructure in graphene sheets via hydrothermal method plus a subsequent annealing process. The as-obtained hybrid was characterized by X-ray diffraction, scanning electron microscopy with an energy dispersive spectroscope (EDS), Raman, and UV–vis diffuse reflectance spectra, respectively. The photoelectrochemical activities and photocatalytic degradation performance of methyl orange under the illumination of ultraviolet light were investigated, and the flocculent-like TiO 2 /graphene composites was found to have a superior photocatalytic activity compared to flocculent-like titanate nanostructure and commercial anatase TiO 2 powder, which can be attributed to the improved light absorption and extremely efficient charge separation of the hybrid structure. The results suggest that the as-prepared flocculent-like TiO 2 /graphene composite is a promising photocatalyst for photoelectrochemical hydrogen production and pollution removal.

A novel graphene/MoS 2 hybrid structure composed of reduced graphene oxide and MoS 2 nanosheets has been successfully prepared via a facile one-step hydrothermal method. Under the hydrothermal treatment, pristine graphene oxide is reduced and tightly covered with liquid-exfoliated MoS 2 nanosheets. The microstructures and properties have been examined by X-ray diffraction, scanning electron microscopy and Raman spectra. It is found that ultrathin MoS 2 nanosheets with high crystallinity are located on the reduced graphene oxide. The obtained MoS 2 /graphene hybrid structure exhibits preferable photoresponse activity under the illumination of ultraviolet light compared to hybrid materials of MoS 2 bulk and reduced graphene oxide. The improved photoresponse can be attributed to the extremely efficient charge separation, as well as MoS 2 nanostructures of the hybrid structure.

Large-size 2D black phosphorus (BP) nanosheets have been successfully synthesized by a facile liquid exfoliation method. The as-prepared BP nanosheets are used to fabricate electrodes for a self-powered photodetector and exhibit preferable photoresponse activity as well as environmental robustness. Photoelectrochemical (PEC) tests demonstrate that the current density of BP nanosheets can reach up to 265 nA cm−2 under light irradiation, while the dark current densities fluctuate near 1 nA cm−2 in 0.1 M KOH. UV–vis and Raman spectra are carried out and confirm the inherent optical and physical properties of BP nanosheets. In addition, the cycle stability measurement exhibits no detectable distinction after processing 50 and 100 cycles, while an excellent on/off behavior is still preserved even after one month. Furthermore, the PEC performance of BP nanosheets-based photodetector is evaluated in various KOH concentrations, which demonstrates that the as-prepared BP nanosheets may have a great potential application in self-powered photodetector. It is anticipated that the present work can provide fundamental acknowledgement of the performance of a PEC-type BP nanosheets-based photodetector, offering extendable availabilities for 2D BP-based heterostructures to construct high-performance PEC devices.

We experimentally investigated the nonlinear optical response in few-layer oxidized black phosphorus (OBP) by the femtosecond Z-scan measurement technique, and found that OBP not only possesses strong ultrafast saturable absorption but also a nonlinear self-defocusing effect that is absent in black phosphorus (BP). The saturable absorption property originates mainly from the direct band structure, which is still maintained in OBP. The emergence of self-defocusing might originate from the combined consequences of the oxygen-induced defects in BP. Our experimental findings might constitute the first experimental evidence on how to dynamically tune its nonlinear property, offering an inroad in tailoring its optical properties through chemical modification (oxidation, introducing defects, etc.). The versatile ultrafast nonlinear optical properties (saturable absorption and self-defocusing) imply a significant potential of the layered OBP in the development of unprecedented optoelectronic devices, such as mode lockers, optical switches, laser beam shapers, and wavelength converters.

2D photocatalytic TiO2/MoS2 hybrid nanosheets (HNs) have been prepared via a facile hydrothermal process. X-ray diffraction patterns and Raman spectra are carried out and confirm a well crystalized anatase and 2H-MoS2 hybridization. Additional morphological and microstructural tests verify a distinct MoS2 framework, indicating the relatively stability of the MoS2 nanosheet platform with a high specific surface area. UV–vis spectra and electrochemical impedance spectra exhibit an enhanced light absorption ability and conductivity of TiO2/MoS2 compared to that of just TiO2. Photoelectrochemical (PEC) tests also demonstrate the photocurrent of 20 : 1 TiO2/MoS2 HNs is greatly improved compared to that of as-prepared TiO2. The saturation current density is about 33 µA cm−2 when the applied potential is 0.2 V, which is nearly twice that of pure TiO2 and four times as high as 5 : 1 TiO2/MoS2 HNs and 1 : 1 TiO2/MoS2 HNs. Besides that, the duration test exhibits no detectable distinction after processing 25 cycles. The improved photocatalytic activities are perhaps derived from the high conductivity and the increased active sites for the introduction of co-catalytic MoS2 nanosheets as well as the positive synergetic effect between the TiO2 and MoS2. This work demonstrates that the as-prepared TiO2/MoS2 HNs may have a great potential application in PEC hydrogen production.

Based on first-principles calculations in the framework of van der Waals density functional theory, we investigate the structural, electronic properties and band-gap tuning of the h-BN/MoS2/h-BN sandwich heterostructure under an external electric field. We find that, different from the suspended monolayer MoS2 with a direct band-gap, h-BN/MoS2/h-BN has an indirect band-gap. Particular attention has been focused on the engineering of the band-gap of the h-BN/MoS2/h-BN heterostructure via application of an external electric field. With the increase of electric field, the band-gap of the h-BN/MoS2/h-BN heterostructure undergoes an indirect-to-direct band-gap transition. Once the electric field intensity is larger than 0.1 V A−1, the gap value of direct band-gap shrinks almost linearly with the field-strength, which indicates that the h-BN/MoS2/h-BN heterostructure is a viable candidate for optoelectronic applications.

We have carried out first-principles calculations and theoretical analysis to explore the structural and electronic properties of MoS2/n-h-BN heterostructures consisting of monolayer MoS2 on top of h-BN substrates with one to five layers. We find that the MoS2/n-h-BN heterostructures show indirect bandgap features with both of CBM (in the K point) and VBM (in the ? point) localized on the monolayer MoS2. Difference charge density and surface bands indicate there is no obvious charge exchange in the heterostructure systems. We show that the changes from a direct bandgap in monolayer free-stranding MoS2 to an indirect bandgap in MoS2/n-h-BN heterostructure is induced by the strain. Moreover, we find that the bandgaps of MoS2/n-h-BN heterostructures decrease with increasing number of h-BN layers, which is proposed to result from the different strain distributions in MoS2 due to the varieties of lattice mismatch rates between MoS2 and h-BN layers. Our results suggest that the MoS2/n-h-BN heterostructure could serve as a prototypical example for band structure engineering of 2D crystals with atomic layer precision.