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.
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.
Superexchange effects play an important role in the determination of crystal structures; however, there has been much less reported on how they determine the stability of clusters. Using evolutionary search strategies and DFT+U (density functional theory with the Hubbard U correction) calculations, we investigate the global minimum-energy structures of Fe12On clusters. Among predicted Fe12On clusters, a cage-shaped Fe12O12 cluster with unexpected stability was observed. In addition, the bare Fe12O12 cluster is shown to possess an extremely large energy gap (2.00 eV), which is greater than that of C60, Au20 and Al13?clusters. Using a Heisenberg model, we traced the origin of the unexpected stability of the bare Fe12O12 cluster to magnetic competition between the nearest-neighbor exchange constant J1 and the next-nearest neighbor exchange constant J2 that was induced by the superexchange interactions. The bare Fe12O12 cluster is thus a unique molecule that is stable and chemically inert.
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.
Iron oxides have attracted considerable interest as abundant materials for high-capacity Li-ion battery anodes. However, their fast capacity fading owing to poorly controlled reversibility of the conversion reactions greatly hinders their application. Here, a sandwich-structured nanocomposite of N-doped graphene and nearly monodisperse Fe3O4 nanoparticles were developed as high-performance Li-ion battery anode. N-doped graphene serves as a conducting framework for the self-assembled structure and controls Fe3O4 nucleation through the interaction of N dopants, surfactant molecules, and iron precursors. Fe3O4 nanoparticles were well dispersed with a uniform diameter of ~15 nm. The unique sandwich structure enables good electron conductivity and Li-ion accessibility and accommodates a large volume change. Hence, it delivers good cycling reversibility and rate performance with a capacity of ~1,227 mA·h·g–1 and 96.8% capacity retention over 1,000 cycles at a current density of 3 A·g–1. Our work provides an ideal structure design for conversion anodes or other electrode materials requiring a large volume change.
One-dimension carbon self-doping g-C3N4 nanotubes (CNT) with abundant communicating pores were synthesized via thermal polymerization of saturated or supersaturated urea inside the framework of a melamine sponge for the first time. A ～16% improvement in photoelectric conversion efficiency (η) is observed for the devices fabricated with a binary hybrid composite of the obtained CNT and TiO2 compared to pure TiO2 device. The result of EIS analysis reveals that the interfacial resistance of the TiO2-dye|I3?/I? electrolyte interface of TiO2-CNT composite cell is much lower than that of pure TiO2 cell. In addition, the TiO2-CNT composite cell exhibits longer electron recombination time, shorter electron transport time, and higher charge collection efficiency than those of pure TiO2 cell. Systematic investigations reveal that the CNT boosts the light harvesting ability of the photovoltaic devices by enhancing not only the visible light absorption but also the charge separation and transfer.
Systemic thrombolysis with intravenous tissue plasminogen activator (tPA) remains the only proven treatment that is effective in improving the clinical outcome of patients with acute ischemic stroke. However, thrombolytic therapy has some major limitations such as hemorrhage, neurotoxicity, and the short time window for the treatment. In this study, we designed iron oxide (Fe3O4) nanorods loaded with 6% tPA, which could be released within ~30 min. The Fe3O4 nanorods could be targeted to blood clots under magnetic guidance. In addition, the release of tPA could be significantly increased using an external rotating magnetic field, which subsequently resulted in a great improvement in the thrombolytic efficiency. Systematic and quantitative studies revealed the fundamental physical processes involved in the enhanced thrombolysis, while the in vitro thrombolysis assay showed that the proposed strategy could improve thrombolysis and recanalization rates and reduce the risk of tPA-mediated hemorrhage in vivo. Such a strategy will be very useful for the treatment of ischemic stroke and other deadly thrombotic diseases such as myocardial infarction and pulmonary embolism in clinical settings.
Multi-shelled CoFe2O4 hollow microspheres with a tunable number of layers (1–4) were successfully synthesized via a facile one-step method using cyclodextrin as a template, followed by calcination. The structural features, including the shell number and shell porosity, were controlled by adjusting the synthesis parameters to produce hollow spheres with excellent capacity and durability. This is a straightforward and general strategy for fabricating metal oxide or bimetallic metal oxide hollow microspheres with a tunable number of shells.
Artificial photosynthesis uses a catalyst to convert CO2 into valuable hydrocarbon products by cleaving the C=O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide (SnO2) nanoparticles and edge-oxidized graphene oxide (eo-GO) sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO2 reduction compared to SnO2 and commercialized TiO2 (P25), respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts.
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.
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.
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.
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.
We report the preparation of nanocomposites of reduced graphene oxide with embedded Fe3O4/Fe nanorings (FeNR@rGO) by chemical hydrothermal growth. We illustrate the use of these nanocomposites as novel electromagnetic wave absorbing materials. The electromagnetic wave absorption properties of the nanocomposites with different compositions were investigated. The preparation procedure and nanocomposite composition were optimized to achieve the best electromagnetic wave absorption properties. Nanocomposites with a GO:α-Fe2O3 mass ratio of 1:1 prepared by annealing in H2/Ar for 3 h exhibited the best properties. This nanocomposite sample (thickness = 4.0 mm) showed a minimum reflectivity of–23.09 dB at 9.16 GHz. The band range was 7.4–11.3 GHz when the reflectivity was less than–10 dB and the spectrum width was up to 3.9 GHz. These figures of merit are typically of the same order of magnitude when compared to the values shown by traditional ferric oxide materials. However, FeNR@rGO can be readily applied as a microwave absorbing material because the production method we propose is highly compatible with mass production standards.
The geometric size and distribution of magnetic nanoparticles are critical to the morphology of graphene (GN) nanocomposites, and thus they can affect the capacity and cycling performance when these composites are used as anode materials in lithium-ion batteries (LiBs). In this work, Fe3O4 nanorods were deposited onto fully extended nitrogen-doped GN sheets from a binary precursor in two steps, a hydrothermal process and an annealing process. This route effectively tuned the Fe3O4 nanorod size distribution and prevented their aggregation. The transformation of the binary precursor was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). XPS analysis indicated the presence of N-doped GN sheets, and that the magnetic nanocrystals were anchored and uniformly distributed on the surface of the flattened N-doped GN sheets. As a high performance anode material, the structure was beneficial for electron transport and exchange, resulting in a large reversible capacity of 929 mA·h·g–1, high-rate capability, improved cycling stability, and higher electrical conductivity. Not only does the result provide a strategy for extending GN composites for use as LiB anode materials, but it also offers a route for the preparation of other oxide nanorods from binary precursors.
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.
Solar-to-H2 conversion is attracting much research attention as a potential approach to meet global renewable energy demands. Although significant advances have been made using metal-tipped colloidal cadmium chalcogenide zero-dimensional (0D) quantum dots and one-dimensional (1D) nanorod heterostructures in solar-to-H2 conversion, their efficiency may be further enhanced using an emerging class of colloidal cadmium chalcogenide nanocrystals, namely two-dimensional (2D) nanoplatelets (NPLs), because of their unique properties. In this review, we summarize the recent advances on exciton dissociation dynamics and light-driven H2 generation performance of colloidal nanoplatelet heterostructures. Following an introduction on the electronic structure of 2D NPLs, we discuss the dynamics of exciton dissociation by electron transfer to molecular acceptors. The exciton quenching dynamics of CdS NPL-Pt and CdSe NPL-Pt heterostructures are compared to highlight the effect of material properties on the relative contributions of the energy-transfer and electron-transfer pathways. Representative solar-to-H2 conversion performances of 2D NPL-metal heterostructures are discussed and compared with those of 1D nanorod-metal heterostructures. Finally, we discuss the challenges in further improving the solar-to-fuel conversion efficiencies of these systems.
Micro-supercapacitors (MSCs) as important on-chip micropower sources have attracted considerable attention because of their unique and advantageous design for optimized maximum functionality within a minimized sized chip and excellent mechanical flexibility/stability in miniaturized portable electronic device applications. In this work, we report a novel, high-performance flexible integrated on-chip MSC based on hybrid nanostructures of reduced graphene oxide/Fe2O3 hollow nanospheres using a microelectronic photo-lithography technology combined with plasma etching technique. The unique structural design for on-chip MSCs enables high-performance enhancements compared with graphene-only devices, exhibiting high specific capacitances of 11.57 F·cm-3 at a scan rate of 200 mV·s-1 and excellent rate capability and robust cycling stability with capacitance retention of 92.08% after 32,000 charge/discharge cycles. Moreover, the on-chip MSCs exhibit superior flexibility and outstanding stability even after repetition of charge/discharge cycles under different bending states. As-fabricated highly flexible on-chip MSCs can be easily integrated with CdS nanowire-based photodetectors to form a highly compacted photodetecting system, exhibiting comparable performance to devices driven by conventional external energy storage units.
We developed a strategy based on coordination polymer to synthesize singleatom site Fe/N and S-codoped hierarchical porous carbon (Fe1/N,S-PC). The as-obtained Fe1/N,S-PC exhibited superior oxygen reduction reaction (ORR) performance with a half-wave potential (E1/2, 0.904 V vs. RHE) that was better than that of commercial Pt/C (E1/2, 0.86 V vs. RHE), single-atom site Fe/N-doped hierarchical porous carbon (Fe1/N-PC) without S-doped (E1/2, 0.85 V vs. RHE), and many other nonprecious metal catalysts in alkaline medium. Moreover, the Fe1/N,S-PC revealed high methanol tolerance and firm stability. The excellent electrocatalytic activity of Fe1/N,S-PC is attributed to the synergistic effects from the atomically dispersed porphyrin-like Fe-N4 active sites, the heteroatom codoping (N and S), and the hierarchical porous structure in the carbon materials. The calculation based on density functional theory further indicates that the catalytic performance of Fe1/N,S-PC is better than that of Fe1/N-PC owing to the sulfur doping that yielded different rate-determining steps.
Spinel LiMn2O4 is a widely utilized cathode material for Li-ion batteries. However, its applications are limited by its poor energy density and power density. Herein, a novel hierarchical porous onion-like LiMn2O4(LMO) was prepared to shorten the Li+ diffusion pathway with the presence of uniform pores and nanosized primary particles. The growth mechanism of the porous onion-like LiMn2O4 was analyzed to control the morphology and the crystal structure so that it forms a polyhedral crystal structure with reduced Mn dissolution. In addition, graphene was added to the cathode (LiMn2O4/graphene) to enhance the electronic conductivity. The synthesized LiMn2O4/graphene exhibited an ultrahigh-rate performance of 110.4 mAh·g–1 at 50 C and an outstanding energy density at a high power density, maintaining 379.4 Wh·kg–1 at 25,293 W·kg–1. Besides, it shows durable stability, with only 0.02% decrease in the capacity per cycle at 10 C. Furthermore, the (LiMn2O4/graphene)/graphite full-cell exhibited a high discharge capacity. This work provides a promising method for the preparation of outstanding, integrated cathodes for potential applications in lithium ion batteries.
