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Two-dimensional (2D) ZnSnO3 is a promising candidate for future gas sensors due to its high chemical response and excellent electronic properties. However, the preparation of 2D ZnSnO3 nanosheets by utilizing soluble inorganic salts and nonorganic solvents remains a challenge. In this work, 2D ZnSnO3 was synthesized via a facile graphene oxide (GO)-assisted co-precipitation method, in which inorganic salts in the aqueous phase replaced metal organic salts in a non-aqueous system. Meanwhile, a “dissolution and recrystallization” mechanism was proposed to explain the transformation from 3D nanocubes to 2D nanosheets. In comparison, the 2D ZnSnO3 nanosheets showed a higher response to formaldehyde (HCHO) at low operating temperature (100 °C). The response (Ra/Rg) of the 2D ZnSnO3 sensor to 10 ppm HCHO was as high as 57, which was approximately 5 times the response of the ZnSnO3 nanocubes sensor. However, the ZnSnO3 nanocubes sensor showed better gas sensing performance to ethanol at high temperature (200 °C). Different gas-sensitive properties were attributed to the different gas diffusion and adsorption processes caused by the morphology and nanostructure. Moreover, both sensors could detect either 0.1 ppm HCHO or ethanol at their optimum operating temperature. This work presents a relatively economical method to prepare 2D compound metal oxides, provides a novel “dissolution and recrystallization” mechanism for 2D multi-metal oxide preparation, and sheds light on the great potential of high-efficiency HCHO and/or ethanol gas sensors.

Biosafe wearable healthcare monitor has attracted significant attention owing to their applicability to wearable electronics. However, the narrow sensing range and poor response limit the application of flexible devices for comprehensive monitoring of human health-related physiological signals (i.e. pulse diagnosis). Critical challenges remain in the development of biocompatible materials and the design of flexible bio-integrated platforms for these purposes, targeting performance approaching those of conventional wafer-based technologies and long-term operational stability. In this context, this work presents a robust and flexible MXene/polydopamine (PDA)-composite-film-based pressure sensor in a portable/wearable fashion, which establishes a unique intercalated spherical-like PDA molecules structure, thereby resulting in excellent sensing performance. The MXene/PDA-based pressure sensor has sensitivity of up to 138.8 kPa-1 in the pressure range of 0.18-6.20 kPa with fast response and recovery speed (t1

Low-dimensional ternary copper iodide metal halide with strong quantum confinement effects has made great progress in optoelectronic fields. However, efficient regulation of anisotropic growth of metal halides single crystal still remains a great challenge. Herein, 2 cm size CsCu

Fully exploiting plasmonic coupling of nanostructured metals is an effective method to promote surface-enhanced Raman scattering (SERS) performance for trace detection of molecules. Herein, we prop...

Two-dimensional (2D) ZnSnO

g-C3N4/Cu2O p–n junction composites with different crystal facets were prepared by a simple one-step route, which showed strong facet-dependent photoactivity, where the degradation rate value k for 20% C3N4–Cu2O truncated cubes composites with {100} facets heterojunction was ∼2.5 times higher than that of pure Cu2O truncated cubes. Meanwhile, k value for 20% C3N4–Cu2O octahedra with {111} facets heterojunction exceeds that of pure Cu2O octahedra by a factor of ∼1.9. p–n heterojunctions with type II energy alignment are determined by XPS analysis. Larger band energy offset (0.96 eV for ΔECBO, 1.73 eV for ΔEVBO) was observed in 20% C3N4–Cu2O truncated cubes composites compared with that of 20% C3N4–Cu2O octahedra composites (0.85 eV for ΔECBO, 1.64 eV for ΔEVBO). The bigger band offset means stronger driving force of the electron transfer between Cu2O truncated cubes with {100} facets and C3N4, indicating band alignment of the heterojunction was facet-dependent, the properly larger band offsets between Cu2O...

Transition metal sulfides-based materials, as one type of promising oxygen reduction reaction (ORR) electrocatalysts have drawn increasing attention. Herein, we proposed a facile strategy to prepare iron-cobalt sulfides embedded in N,S-doped mesoporous carbon (FexCo1-xS-T@NS-MC) via in situ polymerization and pyrolysis. Various characterization methods (e.g., Raman, BET, XPS, and electrochemical tests) are used to explore the differences between the microstructure and catalytic activity of these electrocatalysts. Notably, the sample Fe0.5Co0.5S-1000@NS-MC pyrolyzed at 1000 °C with an optimal iron/cobalt molar ratio (x = 0.5) exhibits the best ORR performance, which has the positive onset potential of 0.947 V vs. RHE, half-wave potential of 0.842 V vs. RHE and a large limiting current density of 5.63 mA cm−2. Moreover, the results obtained from RRDE measurements indicate a four-electron process towards ORR for Fe0.5Co0.5S-1000@NS-MC catalyst. The combination and synergy of the controllable active centers (Fe-adjusted Co9S8/CoS with appropriate ratios) and hierarchical porous structures with large specific surface area render the outstanding ORR activity and electrochemical stability. Those results indicate that bimetallic sulfides-based materials are promising as ORR electrocatalysts.

Much effort has been made to develop the semiconductor photocatalysis, but it is still challenging to fabricate low-cost and high-activity photocatalysts. In this study, Hematite (α-Fe 2 O 3 ) with three kinds of morphologies including dodecahedron, tetrakaidecahedron and hexagonal nanoplates have been synthesized without any organic reagents. The photocatalytic performance reveals that the dodecahedron with exposed {1 0 1} facets is superior to the hexagonal nanoplates with predominant exposure of {0 0 1} facets in the case of similar BET surface area. For further enhancement of photocatalytic activity, carbon layer was coated on dodecahedral α-Fe 2 O 3 through the self-polymerization of dopamine and following pyrolysis at 400 °C under Ar flow. Compared with the pristine dodecahedral α-Fe 2 O 3 , the α-Fe 2 O 3 /C composites exhibit stronger visible absorption, lower photoexcited electron-hole pairs recombination rate and better photodegradation activity. The photocatalytic performance showed the degradation rate of α-Fe 2 O 3 -D/4.5C is nearly 6 times higher than pristine α-Fe 2 O 3 , which have great potential for photocatalysis applications.

N-doped porous Fe/Fe3C@C electrocatalysts were prepared by the pyrolysis of the hexamethylenetetramine (HMT)-incorporated MIL-100-Fe at different temperatures (700–1000 °C) under N2 atmosphere. Rotary evaporation of MIL-100-Fe and HMT solution could make more N-enriched HMT molecules enter into the pores of MIL-100-Fe, thus improving nitrogen contents of the final pyrolyzed samples. All pyrolyzed samples show porous textures with middle specific surface areas. The X-ray photoelectron spectroscopy (XPS) results demonstrate the successful introduction of N atoms into carbon framework. Sample Fe-N2-800 prepared by annealing the precursors with the HMT/MIL-100-Fe weight ratio of 2 at 800 °C exhibits the best electrocatalytic activity towards the oxygen reduction reaction (ORR) in terms of onset potential and current density because of high graphitic N and pyridinic N content. The enwrapped Fe/Fe3C nanoparticles and Fe-Nx active sites in these samples could also boost the ORR activity synergistically. Moreover, sample Fe-N2-800 demonstrates a dominant four electron reduction process, as well as excellent long-term operation stability and methanol crossover resistance. Thus, the N-doped Fe/Fe3C@C composites derived from the HMT-incorporated MIL-100-Fe are promising electrocatalysts to replace Pt/C for ORR in practical applications.

As the new display technology, Micro-LEDs are of the advantages of low power consumption, high brightness, high resolution and fast response time. However, the strong surface non-radiative recombination significantly reduces their efficiency. Some techniques such as epitaxial growth or wet sulfide have been introduced to inhibit the surface recombination, but these expensive or unstable methods ignore the operability of industrial production. Herein, we use an ion implantation method to modify the high-density surface defects on the sidewall, thereby improve the luminous efficiency effectively by inhibiting carrier surface non-radiative recombination. The photoelectric performances of GaN-based Micro-LEDs after N ion implantation were studied. The characterization results indicated that the photoluminescence intensity of Micro-LEDs was increased by 7 times after passivation, which was attributed to the significant elimination of sidewall damage. In addition, the removal of the surface dangling bonds and oxidized nitrides (Ga–N or Ga-OH bonds) after the passivation process were further proved by Auger electron spectroscopy characterization. As a result of the N ion implantation, the external quantum efficiency of packaged Micro-LEDs chip increased about 33%. Therefore, this manuscript will provide a new direction for improving the photoelectric performance of Micro-LEDs.

Remarkable bifunctional electrocatalysts for oxygen reaction reduction (ORR) and oxygen evolution reaction (OER) are the key for rechargeable metal-air batteries. In this work, a novel 3D Fe/N-based honeycomb-like carbon with uniformly-distributed active centers were synthesized by agarose and FeCl3 as the precursor, which display excellent ORR performance with large diffusion-limited current density (≈7.5 mA cm−2) and Tafel slope (≈88 mV/dev), significantly superior to the commercial Pt/C electrode. In addition, Fe-NPC-1000 as cathode catalyst in Zn-air battery owns higher power density and charge-discharge stability in comparison with commercial Pt/C catalyst, which shows excellent potential in the realistic application of energy devices.

The micro lighting-emitting diode (Micro-LED) array devices have attracted attention due to increasing demand in augmented reality (AR), virtual reality (VR), LIFI light source, and other micro-display applications. However, with the decrease of micro-LED diameter, the performance of micro-LED is severely limited due to the size effect. In the work, the AlGaInP based red micro-LED with diameter ranging from 2 to 16 μm was prepared to study the size effect of micro-LED array, the array with larger micro-LED diameter show higher external quantum efficiency (EQE), meanwhile, the carrier lifetime decrease with the decreasing of the diameter, which can be explained by more surface states in the micro-LED with smaller diameter. The enhancement of EQE by 2 times has been achieved after surface passivation in (NH4)2Sx solution.

Novel composites composed of α-Fe2O3 tetrakaidecahedrons and graphene oxide have been easily fabricated and demonstrated to be efficient photoelectrodes for photoelectrochemical water splitting reaction with superior photocurrent response. α-Fe2O3 tetrakaidecahedrons are facilely synthesized in a green manner without any organic additives and then modified with graphene oxide. The morphological and structural properties of α-Fe2O3/graphene composite are intensively investigated by several means, such as X-ray diffraction, field-emission scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, Fourier Transform infrared spectroscopy, and Raman spectroscopy. The tetrakaidecahedronal hematite particles have been indicated to be successfully coupled with graphene oxide. Systematical photoelectrochemical and impedance spectroscopy measurements have been carried out to investigate the favorable performance of α-Fe2O3/graphene composites, which are found to be effective photoanodes with rapid, steady, and reproducible feature. The coupling of graphene with α-Fe2O3 particles has greatly enhanced the photoelectrochemical performance, resulting in higher photocurrent and lower onset potential than that of pure α-Fe2O3. This investigation has provided a feasible method to synthesize α-Fe2O3 tetrakaidecahedron and fabricate an efficient α-Fe2O3/graphene photoelectrode for photoelectrochemical water oxidation, suggesting a promising route to design noble metal free semiconductor/graphene photocatalysts.

Photoelectrochemical (PEC) water splitting using solar energy has received widespread attention, and strong performance photocatalysts are highly desired. In this work, uniform carbon-coated CdS nanostructures have been fabricated using ascorbic acid as the carbon source by a facile hydrothermal method and characterized using transmission electron microscopy (TEM). The thickness of the carbon layer can be well controlled by the amount of ascorbic acid added during the reaction. Compared to pristine CdS, carbon-coated CdS nanostructures exhibit stronger light absorption and more efficient electron transfer as determined by absorption and photoluminescence (PL) spectroscopy. Ultrafast charge carrier dynamics in the composite CdS/C structures were studied using femtosecond transient absorption (TA) spectroscopy, which revealed direct evidence of effective charge transfer from CdS to the carbon layer. In addition, the CdS/C composites were employed as photoanodes for PEC hydrogen generation, which showed significant improvement in photoactivity over pristine CdS nanospheres. The photocurrent density (−1.0 V vs. Ag/AgCl) of one of the composite structures, CdS/7-C, exhibited ∼20 times enhancement compared with that of pristine CdS. The enhanced PEC property can be attributed to increased light scattering and consequently the light harvesting throughout the whole spectral wavelength, and the effective electron transfer from CdS to the carbon layer. Such carbon-coated semiconductor composites based on a simple and low-cost synthesis method should be useful in PEC as well as other applications such as photovoltaics, detectors and sensors.

Core–shell CdS/TiO2 structures are promising for solar-to-fuel conversion applications because their ideal type-II band alignment helps effective charge transfer to form the CdS+/TiO2− system. A better understanding of the charge carrier dynamics is critical to provide guiding principles for designing photoelectrochemical (PEC) devices. Hence, TiO2 shell-thickness dependent charge carrier dynamics and competition between electron relaxation in CdS (e.g. recombination and trapping) and electron transfer from CdS to TiO2 were investigated using ultrafast transient absorption (TA) spectroscopy. The results indicate that the CdS/TiO2 nanocomposite with a molar ratio of 2 : 1 exhibits the highest electron transfer rate constant of ET = 2.71 × 1010 s−1, along with an electron relaxation rate of CdS/TiO2 = 3.43 × 1010 s−1, resulting in an electron transfer quantum efficiency of QET = 79%, which also corresponds to the best PEC hydrogen generation in the CdS/TiO2 core–shell composites. However, the electron transfer rate decreases with increasing thickness of the TiO2 shell consisting of aggregated nanoparticles. One possible explanation is that the CdS and TiO2 form relatively larger, separate particles, or less conforming small particles, with poor interfaces with increasing TiO2, thereby reducing electron transfer from CdS to TiO2, which is supported by SEM, and TEM data and consistent with PEC results. The thickness and morphology dependence of electron transfer and relaxation provides new insight into the charge carrier dynamics in such composite structures, which is important for optimizing the efficiency of PEC for solar fuel generation applications.

Scientific Reports 7: Article number: 43599; published online: 08 March 2017; updated: 03 August 2017. The absorption maximum of MO changes upon adsorption to MoS2. Therefore, for calculations of the MO concentration from the absorption spectra shown in Figure 5C of the Article, the authors used λmax ~ 464 nm for time point 0 min and λmax ~ 475 nm for other time points.

Graphene nanodots (GNDs) are one of the most attractive graphene nanostructures due to their tunable optoelectronic properties. Fabricated by polystyrene‐nanosphere lithography, uniformly sized graphene nanodots array (GNDA) is constructed as an ultraviolet photodetector (PD) with ZnO nanofilm spin coated on it. The size of GNDA can be well controlled from 45 to 20 nm varying the etching time. It is revealed in the study that the photoelectric properties of ZnO/GNDA PD are highly GNDA size‐dependent. The highest responsivity (R) and external quantum efficiency of ZnO/GNDA (20 nm) PD are 22.55 mA W−1 and 9.32%, almost twofold of that of ZnO PD. Both ZnO/GNDA (20 nm) PD and ZnO/GNDA (30 nm) PD exhibit much faster response speed under on/off switching light and have shorter rise/decay time compared with ZnO PD. However, as the size of GNDA increase to 45 nm, the PD appears poor performance. The size‐dependent phenomenon can be explained by the energy band alignments in ZnO/GNDA hybrids. These efforts reveal the enhancement of GNDs on traditional photodetectors with tunable optoelectronic properties and hold great potential to pave a new way to explore the various remarkable photodetection performances by controlling the size of the nanostructures.

Herein we report superior dye-adsorption performance for flower-like nanostructure composed of two dimensional (2D) MoS2 nanosheets by a facile hydrothermal method, more prominent adsorption of cationic dye compared with anodic dye indicates the dye adsorption performance strongly depends on surface charge of MoS2 nanosheets. The adsorption mechanism of dye is analyzed, the kinetic data of dye adsorption fit well with the pseudo-second-order model, meanwhile adsorption capability at different equilibrium concentrations follows Langmuir model, indicating the favorability and feasibility of dye adsorption. The regenerable property for MoS2 with full adsorption of dye molecules by using alkaline solution were demonstrated, showing the feasibility of reuse for the MoS2, which is promising in its practical water treatment application.

There has been significant progress in the field of semiconductor photocatalysis, but it is still a challenge to fabricate low-cost and high-activity photocatalysts because of safety issues and nonsecondary pollution to the environment. Here, 2D hexagonal nanoplates of -Fe2O3/graphene composites with relatively good distribution are synthesized for the first time using a simple, one-step, template-free, hydrothermal method that achieves the effective reduction of the graphene oxide (GO) to graphene and intimate and large contact interfaces of the -Fe2O3 nanoplates with graphene. The - Fe2O3/graphene composites showed significantly enhancement in the photocatalytic activity compared with the pure -Fe2O3 nanoplates. At an optimal ratio of 5 wt% graphene, 98% of Rhodamine (RhB) is decomposed with 20 min of irradiation, and the rate constant of the composites is almost four times higher than that of pure -Fe2O3 nanoplates. The decisive factors in improving the photocatalytic performance are the intimate and large contact interfaces between 2D hexagonal -Fe2O3 nanoplates and graphene, in addition to the high electron withdrawing/storing ability and the highconductivity of reduced graphene oxide (RGO) formed during the hydrothermal reaction. The effective charge transfer from -Fe2O3 nanoplates to graphene sheets is demonstrated by the significant weakening of photoluminescence in -Fe2O3/graphene composites.

Changing the solvent and environmental conditions during the preparation of CdS nanoparticles have a marked effect on the crystal structure, size distribution, nanoparticle size, absorption and emission properties. X-ray investigations revealed that the CdS nanoparticles prepared with high surface tension solvent have clearly identified hexagonal structure. However, the nanoparticles prepared with high dipole moment solvent matched a cubic structure better than a hexagonal one. Optical absorption measurements proved that CdS nanoparticles prepared in aprotic solvent showed an increase in both size of nanoparticles and size polydispersity index (SPI) with a decrease of the dipole moment, viscosity and surface tension of the solvent, which are applicable to the nanoparticles prepared under argon and ambient atmospheres. Fluorescence spectroscopy showed that the CdS nanoparticles synthesized in aprotic solvent with high dipole moment revealed a high intensity band edge emission blue band with a small half width. Also, the increase of the dipole moment of the solvent leads to a decrease in the Stokes shift for CdS nanoparticles prepared under an argon atmosphere.

A novel type of hierarchical nanocomposites consisted of MoS2 nanosheet coating on the self-ordered TiO2 nanotube arrays is successfully prepared by a facile combination of anodization and hydrothermal methods. The MoS2 nanosheets are uniformly decorated on the tube top surface and the intertubular voids with film appearance changing from brown to black color. Anatase TiO2 nanotube arrays (NTAs) with clean top surfaces and the appropriate amount of MoS2 precursors are key to the growth of perfect compositing TiO2 @MoS2 hybrids with significantly enhanced photocatalytic activity and photocurrent response. These results reveal that the strategy provides a flexible and straightforward route for design and preparation nanocomposites based on functional semiconducting nanostructures with 1D self-ordered TiO2 NTAs, promising for new opportunities in energy/environment applications, including photocatalysts and other photovoltaic devices.

The treatment of environmental pollution has become one of the most critical issues in the world. Despite the progress made in the study of semiconductor photocatalysis, it is still a challenge to obtain photocatalysts with high activity through relatively simple fabrication processes. In this work, monodisperse CdS spherical nanoparticles (SNPs) of various sizes and good crystallinity are obtained by only adjusting the starting ratio of reactants and the reaction temperature, exhibiting high photocatalytic performances. The photocatalytic rate constant of the approximate to 100 nm CdS SNPs, especially, is more than double that of P25. Furthermore, 3-mercaptopropyltrimethoxysilane is used to assist the interaction between approximate to 200 nm CdS SNPs and citrate-stabilized Au nanoparticles (NPs). The significant increase of photocatalytic activity is confirmed by the degradation of Rodamine B (RhB) under Xe light irradiation. At the optimal Au concentration (0.5 wt%), the prepared nanohybrids show the highest photocatalytic activity, exceeding that of pure CdS two times. The superior photocatalytic performances of the CdS SNPs-Au nanohybrids can be attributed to the intimate interfacial contact between CdS SNPs and Au NPs, which is a contributing factor to the improvement of transfer and the fate of photogenerated charge carriers from CdS SNPs to Au NPs. Refereed/Peer-reviewed