In-plane symmetry is an important contributor to the physical properties of two-dimensional layered materials, as well as atomically thin heterojunctions. Here, we demonstrate anisotropic/isotropic van der Waals (vdW) heterostructures of ReS2 and MoS2 monolayers, where interlayer coupling interactions and charge separation were observed by in situ Raman-photoluminescence spectroscopy, electrical, and photoelectrical measurements. We believe that these results could be helpful for understanding the fundamental physics of atomically thin vdW heterostructures and creating novel electronic and optoelectronic devices.
Bismuth telluride (Bi2Te3) is one of the most important commercial thermoelectric materials. In recent years, the discovery of topologically protected surface states in Bi chalcogenides has paved the way for their application in nanoelectronics. Determination of the fracture toughness plays a crucial role for the potential application of topological insulators in flexible electronics and nanoelectromechanical devices. Using depth-sensing nanoindentation tests, we investigated for the first time the fracture toughness of bulk single crystals of Bi2Te3 topological insulators, grown using the Bridgman-Stockbarger method. Our results highlight one of the possible pitfalls of the technology based on topological insulators.
The size and density of Ag nanoparticles on n-layer MoS2 exhibit thicknessdependent behavior. The size and density of these particles increased and decreased, respectively, with increasing layer number (n) of n-layer MoS2. Furthermore, the surface-enhanced Raman scattering (SERS) of Ag on this substrate was observed. The enhancement factor of this scattering varied with the thickness of MoS2. The mechanisms governing the aforementioned thickness dependences are proposed and discussed.
The construction of metal sulfides-carbon nanocomposites with a hollow structure is highly attractive for various energy storage and conversion technologies. Herein, we report a facile two-step method for preparing a nanocomposite with CoS2 nanoparticles in N-doped carbon nanotube hollow frameworks (NCNTFs). Starting from zeolitic imidazolate framework-67 (ZIF-67) particles, in situ reduced metallic cobalt nanocrystals expedite the formation of the hierarchical hollow frameworks from staggered carbon nanotubes via a carbonization process. After a follow-up sulfidation reaction with sulfur powder, the embedded cobalt crystals are transformed into CoS2 nanoparticles. Benefitting from the robust hollow frameworks made of N-doped carbon nanotubes and highly active CoS2 ultrafine nanoparticles, this advanced nanocomposite shows greatly enhanced lithium storage properties when evaluated as an electrode for lithium-ion batteries. Impressively, the resultant CoS2/NCNTF material delivers a high specific capacity of ～937 mAh·g–1 at a current density of 1.0 A·g–1 with a cycle life longer than 160 cycles.
Manipulating the alignment of liquid crystals (LCs) is a hot and fundamental issue for their applications in block copolymers, photonics, actuators, biosensors, and liquid-crystal displays. Here, the surface characteristic of Cu2O nanocrystals was well controlled to manipulate the orientation of the LCs. The mechanism of the orientation of the LCs induced by Cu2O nanocrystals was elucidated based on the interaction between the LCs and Cu2O nanocrystals. To comprehensively prove our assumption, different types of LCs (nematic, cholesteric, and smectic) as well as the same type of LCs with different polarities were selected in our system. Moreover, the photomechanical behaviors of the LC polymer composites demonstrated that the alignment of LCs can be effectively manipulated using Cu2O nanocrystals.
Two-dimensional ZrS2 materials have potential for applications in nanoelectronics because of their theoretically predicted high mobility and sheet current density. Herein, we report the thickness and temperature dependent transport properties of ZrS2 multilayers that were directly deposited on hexagonal boron nitride (h-BN) by chemical vapor deposition. Hysteresis-free gate sweeping, metalinsulator transition, and T–γ (γ ~ 0.82–1.26) temperature dependent mobility were observed in the ZrS2 films.
Nanomaterials with unique edge sites have received increasing attention due to their superior performance in various applications. Herein, we employed an effective ethylenediaminetetraacetic acid (EDTA)-assisted method to synthesize a series of exotic Bi2Se3 nanostructures with distinct edge sites. It was found that the products changed from smooth nanoplates to half-plate-containing and crown-like nanoplates upon increasing the molar ratio of EDTA to Bi3+. Mechanistic studies indicated that, when a dislocation source and relatively high supersaturation exist, the step edges in the initially formed seeds can serve as supporting sites for the growth of epilayers, leading to the formation of half-plate-containing nanoplates. In contrast, when the dislocation source and a suitably low supersaturation are simultaneously present in the system, the dislocation-driven growth mode dominates the process, in which the step edges form at the later stage of the growth responsible for the formation of crown-like nanoplates.
A facile approach for the heterogenization of transition metal catalysts using non-covalent interactions in hollow click-based porous organic polymers (H-CPPs) is presented. A catalytically active cationic species, [Ru(bpy)3]2+ (bpy = 2,2’-bipyridyl), was immobilized in H-CPPs via electrostatic interactions. The intrinsic properties of [Ru(bpy)3]2+ were well retained. The resulting Rucontaining hollow polymers exhibited excellent catalytic activity, enhanced stability, and good recyclability when used for the oxidative hydroxylation of 4-methoxyphenylboronic acid to 4-methoxyphenol under visible-light irradiation. The attractive catalytic performance mainly resulted from efficient mass transfer and the maintenance of the chemical properties of the cationic Ru complex in the H-CPPs.
Recently, the electrochemical N2 reduction reaction (NRR) in aqueous electrolytes at ambient temperature and pressure has demonstrated its unique advantages and potentials. The reactants are directly derived from gaseous N2 and water, which are naturally abundant, and NH3 production is important for fertilizers and other industrial applications. To improve the conversion yield and selectivity (mainly competing with water reduction), electrocatalysts must be rationally designed to optimize the mass transport, chemisorption, and transduction pathways of protons and electrons. In this review, we summarize recent progress in the electrochemical NRR. Studies of electrocatalyst designs are summarized for different categories, including metal-based catalysts, metal oxide-derived catalysts, and hybrid catalysts. Strategies for enhancing the NRR performance based on the facet orientation, metal oxide interface, crystallinity, and nitrogen vacancies are presented. Additional system designs, such as lithium-nitrogen batteries, and the solvent effect are introduced. Finally, existing challenges and prospects are discussed.
Nanosized metal (Pt or Pd)-decorated TiO2 nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO2 NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO2 under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO2 NFs were found to exhibit enhanced performance compared to Pt-decorated TiO2 NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO2 NFs exhibited higher selectivity for methanol, typically producing ～90 ppmg?1·h?1 methanol. The CO2 photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.
In this paper, we describe the facile and effective preparation of a series of cobalt-doped Fe3O4 nanocatalysts via chemical coprecipitation in an aqueous solution. The catalyst allowed the hydrogenation of chloronitrobenzenes to chloroanilines (CAs) to proceed at low temperatures in absolute water and at atmospheric pressure, resulting in approximately 100% yield and selectivity. Several factors that influence the yield of CAs were investigated. The results showed that the suitable dosage of the catalyst was ~10 mol.% of the substrate, and the optimal reaction time, reaction temperature, and reaction pressure were 20 min, 80 °C, and atmospheric pressure, respectively. Under the optimal reaction conditions, the CA yield was as high as 98.4%, and the nitro reduction rate reached 100%, which indicates the excellent selectivity of the homemade catalyst. This process also overcomes the environmental pollution harms associated with the traditional process.
A facile inside-out Ostwald ripening route to the morphology-controlled preparation of TiO2 microspheres is developed. Here, TiO2 hollow microspheres (HM) and solid microspheres (SM) are prepared by adjusting the volume ratio of isopropanol (IPA) to acetylacetone (Acac) in the solvothermal process. During the formation process of HM, precipitation of solid cores, subsequent deposition of outer shells on the surface of cores, and simultaneous core dissolution and shell recrystallization are observed, which validate the inside-out Ostwald ripening mechanism. Design and optimization of the properties (pore size, surface area, and trap state) of TiO2 microspheres are vital to the high performance of dyesensitized solar cells (DSSCs). The optimized TiO2 microspheres (rHM and rSM) obtained by post-processing on recrystallization, possess large pore sizes, high surface areas and reduced trap states (Ti3+ and oxygen vacancy), and are thus ideal materials for photovoltaic devices. The power conversion efficiency of DSSCs fabricated using rHM photoanode is 11.22%, which is significantly improved compared with the 10.54% efficiency of the rSM-based DSSC. Our work provides a strategy for synthesizing TiO2 microspheres that simultaneously accommodate different physical properties, in terms of surface area, crystallinity, morphology, and mesoporosity.
We systematically investigated the development of film morphology and crystallinity of methyl-ammonium bismuth (III) iodide (MA3Bi2I9) through onestep spin-coating on TiO2-deposited indium tin oxide (ITO)/glass. The precursor solution concentration and substrate structure have been demonstrated to be critically important in the active-layer evolution of the MA3Bi2I9-based solar cell. This work successfully improved the cell efficiency to 0.42% (average: 0.38%) with the mesoscopic architecture of ITO/compact-TiO2/mesoscopic-TiO2 (meso-TiO2)/MA3Bi2I9/2,2′,7,7′-tetrakis(N,N-di-4-methoxyphenylamino)-9,9′spiro-bifluorene (spiro-MeOTAD)/MoO3/Ag under a precursor concentration of 0.45 M, which provided the probability of further improving the efficiency of the Bi3+-based lead-free organic–inorganic hybrid solar cells.
Nanomaterials with electrochemical activity are always suffering from aggregations, particularly during the high-temperature synthesis processes, which will lead to decreased energy-storage performance. Here, hierarchically structured lithium titanate/nitrogen-doped porous graphene fiber nanocomposites were synthesized by using confined growth of Li4Ti5O12 (LTO) nanoparticles in nitrogen-doped mesoporous graphene fibers (NPGF). NPGFs with uniform pore structure are used as templates for hosting LTO precursors, followed by high-temperature treatment at 800 °C under argon (Ar). LTO nanoparticles with size of several nanometers are successfully synthesized in the mesopores of NPGFs, forming nanostructured LTO/NPGF composite fibers. As an anode material for lithium-ion batteries, such nanocomposite architecture offers effective electron and ion transport, and robust structure. Such nanocomposites in the electrodes delivered a high reversible capacity (164 mAh·g–1 at 0.3 C), excellent rate capability (102 mAh·g–1 at 10 C), and long cycling stability.
Yolk/shell nanoparticles (NPs), which integrate functional cores (likes Fe3O4) and an inert SiO2 shell, are very important for applications in fields such as biomedicine and catalysis. An acidic medium is an excellent etchant to achieve hollow SiO2 but harmful to most functional cores. Reported here is a method for preparing sub-100 nm yolk/shell Fe3O4@SiO2 NPs by a mild acidic etching strategy. Our results demonstrate that establishment of a dissolution–diffusion equilibrium of silica is essential for achieving yolk/shell Fe3O4@SiO2 NPs. A uniform increase in the silica compactness from the inside to the outside and an appropriate pH value of the etchant are the main factors controlling the thickness and cavity of the SiO2 shell. Under our “standard etching code”, the acid-sensitive Fe3O4 core can be perfectly preserved and the SiO2 shell can be selectively etched away. The mechanism of regulation of SiO2 etching and acidic etching was investigated.
Catalytic hydrogenation is an important process in the chemical industry. Traditional catalysts require the effective cleavage of hydrogen molecules on the metal-catalyst surface, which is difficult to achieve with non-noble metal catalysts. In this work, we report a new hydrogenation method based on water/proton reduction, which is completely different from the catalytic cleavage of hydrogen molecules. Active hydrogen species and photo-generated electrons can be directly applied to the hydrogenation process with Cu1.94S-Zn0.23Cd0.77S semiconductor heterojunction nanorods. Nitrobenzene, with a variety of substituent groups, can be efficiently reduced to the corresponding aniline without the addition of hydrogen gas. This is a novel and direct pathway for hydrogenation using non-noble metal catalysts.
Because of the coupling between semiconducting and piezoelectric properties in wurtzite materials, strain-induced piezo-charges can tune the charge transport across the interface or junction, which is referred to as the piezotronic effect. For devices whose dimension is much smaller than the mean free path of carriers (such as a single atomic layer of MoS2), ballistic transport occurs. In this study, transport in the monolayer MoS2 piezotronic transistor is studied by presenting analytical solutions for two-dimensional (2D) MoS2. Furthermore, a numerical simulation for guiding future 2D piezotronic nanodevice design is presented.
Hollow nanostructures have attracted considerable attention owing to their large surface area, tunable cavity, and low density. In this study, a unique flower-like C@SnOX@C hollow nanostructure (denoted as C@SnOX@C-1) was synthesized through a novel one-pot approach. The C@SnOX@C-1 had a hollow carbon core and interlaced petals on the shell. Each petal was a SnO2 nanosheet coated with an ultrathin carbon layer ~2 nm thick. The generation of the hollow carbon core, the growth of the SnO2 nanosheets, and the coating of the carbon layers were simultaneously completed via a hydrothermal process using resorcinol-formaldehyde resin-coated SiO2 nanospheres, tin chloride, urea, and glucose as precursors. The resultant architecture with a large surface area exhibited excellent lithium-storage performance, delivering a high reversible capacity of 756.9 mA·h·g–1 at a current density of 100 mA·g–1 after 100 cycles.
The assembly of hybrid nanomaterials has opened up a new direction for the construction of high-performance anodes for lithium-ion batteries (LIBs). In this work, we present a straightforward, eco-friendly, one-step hydrothermal protocol for the synthesis of a new type of Fe2O3-SnO2/graphene hybrid, in which zero-dimensional (0D) SnO2 nanoparticles with an average diameter of 8 nm and one-dimensional (1D) Fe2O3 nanorods with a length of ~150 nm are homogeneously attached onto two-dimensional (2D) reduced graphene oxide nanosheets, generating a unique point-line-plane (0D-1D-2D) architecture. The achieved Fe2O3-SnO2/graphene exhibits a well-defined morphology, a uniform size, and good monodispersity. As anode materials for LIBs, the hybrids exhibit a remarkable reversible capacity of 1,530 mA·g?1 at a current density of 100 mA·g?1 after 200 cycles, as well as a high rate capability of 615 mAh·g?1 at 2,000 mA·g?1. Detailed characterizations reveal that the superior lithium-storage capacity and good cycle stability of the hybrids arise from their peculiar hybrid nanostructure and conductive graphene matrix, as well as the synergistic interaction among the components.
Triangular Ni(HCO3)2 nanosheets were synthesized via a template-free solvothermal method. The phase transition and formation mechanism were explored systematically. Further investigation indicated that the reaction time and pH have significant effects on the morphology and size distribution of the triangular Ni(HCO3)2 nanosheets. More interestingly, the resulting product had an ultra-thin structure and high specific surface area, which can effectively accelerate the charge transport during charge–discharge processes. As a result, the triangular Ni(HCO3)2 nanosheets not only exhibited high specific capacitance (1,797 F·g-1 at 5 A·g-1 and 1,060 F·g-1 at 50 A·g-1), but also showed excellent cycling stability with a high current density (~80% capacitance retention after 5,000 cycles at the current density of 20 A·g-1).
