Constructing efficient HCSs/Nb3O7F hybrids based on bonding interaction to boost simulated-sunlight photocatalytic performance.

Recently, Nb3O7F (NOF) semiconductor has been intensively studied owing to its excellent ultraviolet activity, good thermal stability and low carrier recombination. In this work, we report a five-step technique to synthesize hollow carbon spheres (HCSs)/NOF hybrids. Activating the surface of HCSs by creating oxyfluorinated functionalization can easily trigger an interaction between oxyfluorinated HCSs and NOF intermediates, finally resulting in the formation of HCSs/NOF hybrids. By manipulating the contents of HCSs with unexceptionable electron mobility, the hybrids can simultaneously achieve narrower band gap, stronger light absorption and rapider charge transfer. As a consequence, HCSs/NOF hybrids exhibit enhanced photodegradation performance towards RhB solutions under simulated sunlight irradiation. Specially, HCSs/NOF-1.0 catalysts with 95.7% degradation efficiency within 40 min demonstrate approximately four times higher photocatalytic activity than that of pure NOF catalysts. The results may offer new inspirations for a design of novel catalysts with higher photoactivity.

In†Situ Corrosion Fabrication of NaNbO3 /Nb3 O7 F Heterojunctions with Optimized Band Realignment for Enhanced Photocatalytic Hydrogen Evolution.

Heterostructured photocatalysis is a significant issue owing to the unique band alignment, improved spectrum absorption, and enhanced photocatalytic activity. However, the construction of uniform, controllable, and effective heterojunctions is still a huge challenge. Herein, NaNbO3 /Nb3 O7 F heterojunctions are fabricated through an in situ corrosion technique for the first time. The influence of phase transformation on the hydrogen evolution reaction (HER) activity is investigated systematically in terms of photocatalytic water splitting for H2 production. Interestingly, the band realignment and good interfacial contact endow the NaNbO3 /Nb3 O7 F heterojunctions with a high HER activity (43.3 mmol g-1 h-1 ), which is about 2.4 times that of pure Nb3 O7 F and 1.36 times that of pure NaNbO3 . The results may provide some new insights into the corrosion technique and HER activity of novel heterostructured catalysts.

Boosted visible-light photocatalytic activity and retarded carrier recombination of Eu3+-doped Nb3O7F nanomaterials prepared by hydrothermal method.

Novel trivalent europium (Eu3+)-doped niobium oxyfluoride (Nb3O7F) nanomaterials with retarded carrier recombination and enhanced photocatalytic activity were successfully synthesized by a facile hydrothermal method. Through changing the doping ratio of Eu3+ ions, the phase, composition, morphology, absorption spectra and photocatalytic properties were investigated in detail. The results showed that Eu3+ ions were successfully incorporated into the interstitial sites of Nb3O7F crystal lattice. With the increase of Eu3+ amounts, the morphology gradually changed from nanowall to irregular nanoparticle. Meanwhile, incorporation of Eu3+ ions had a slight influence on the light absorption. However, Eu3+-doped samples exhibited excellent photodegradation activity towards Rhodamine B dyes. The improvement may be ascribed to higher specific surface area, and lower carrier recombination prohibited by forming Eu3+/Eu2+ self-redox centers. This work envisages that Eu3+-doped Nb3O7F nanomaterials may be a promising kind of photocatalysts.

Emission of terahertz plasmons from driven electrons in grated graphene.

Terahertz plasmon emission is the key to getting terahertz radiation, which has resulted in numerous studies on it. In this paper, we present the results of a theoretical investigation of terahertz plasmon emission by drifting electrons in a grated graphene system driven by an electric field by applying the Boltzmann's equilibrium equation method. The results show that plasmon frequencies from terahertz to infrared are generated by drifting electrons through the interaction between plasmons and electrons. Obvious increase of the plasmon emission strength with the driving electric field can be seen when the electric field is more than a certain strength (e.g. 1.0 kV/cm). The effects of electron density and the grating period on the emission strength of plasmons were also investigated. It was found that terahertz plasmons can be obtained by applying a grating with appropriate period. The plasmon frequencies can be tuned using either the driving electric field or the electron density controlled by the gate voltage or the grating parameters. This work may help to gain insight into graphene plasmonics and be pertinent to the application of graphene-based structures as electrically tunable terahertz plasmonic devices.

Unexpected stable phases of tungsten borides.

Tungsten borides are a unique class of compounds with excellent mechanical properties comparable to those of traditional superhard materials. However, the in-depth understanding of these compounds is hindered by the uncertainty of their phase relations and complex crystal structures. Here, we explored the W-B system systematically by ab initio variable-composition evolutionary simulations at pressures from 0 to 40 GPa. Our calculations successfully found all known stable compounds and discovered two novel stable phases, P4[combining macron]21m-WB and P21/m-W2B3, and three nearly stable phases, R3m-W2B5, Ama2-W6B5, and Pmmn-WB5, at ambient pressure and zero Kelvin. Interestingly, P4[combining macron]21m-WB is much harder than the known α and ß phases, while Pmmn-WB5 exhibits the highest hardness. Furthermore, it is revealed that the much debated WB4 becomes stable as the P63/mmc (2 f.u. per unit cell) phase at pressures above ∼1 GPa, not at ambient pressure as reported previously. Our findings provide important insights for understanding the rich and complex crystal structures of tungsten borides, and indicate WB2, WB4, and WB5 as compounds with the most interesting mechanical properties.

Tunable band alignment in two-phase-coexistence Nb3O7F nanocrystals with enhanced light harvesting and photocatalytic performance.

A two-phase-coexistence technique offers intriguing variables to maneuver novel and enhanced functionality in a single-component material. Most importantly, new band alignment and perfect interfaces between two phases can strongly affect local photoelectronic properties. However, previous efforts to achieve two-phase coexistence were mainly restricted to specific systems and methods. Here we demonstrate a phase-transition route to acquire two-phase-coexistence niobium oxyfluoride (Nb3O7F) nanocrystals for the first time. Based on key distinguishing features of the experimental results and theoretical analysis, the phase transition of Nb3O7F involves an organic/inorganic hybrid, heat treating, Al-doping, lattice deformation and structural rearrangement. The band gap can be effectively tuned from 3.03 eV to 2.84 eV, and the VBM can be tuned from 1.49 eV to 1.69 eV according to the phase proportion. Benefiting from uniform nanocrystal size, tunable band alignment and an optimized interfacial structure, the two-phase coexistence markedly enhances visible-light harvesting and the photocatalytic performance of Nb3O7F nanocrystals. The results not only demonstrate an opportunity to explore two-phase coexistence of novel nanocrystals, but also illustrate the role of two-phase coexistence in achieving enhanced photoelectronic properties.

A Simple Approach for Synthesizing of Fluorescent Carbon Quantum Dots from Tofu Wastewater.

We present an investigation on carbon quantum dots (CQDs) synthesized from wastewater induced during the production of tofu. We find that tofu wastewater is a good source of raw material in making fluorescent CQDs. The corresponding CQDs can be fabricated simply via hydrothermal reaction to carbonize the organic matter in the yellow serofluid of tofu wastewater. Two sorts of CQDs can be obtained within the deionized water and NaOH solution, respectively, where the CQDs in water (NaOH solution) can emit blue (green) light under the UV irradiation. It is found from X-ray photoelectron spectroscopy (XPS) that the basic difference between these two sorts of CQDs is the contents of C-O and C=O bonds on the surface of the CQDs. This difference can cause different features of the photoluminescence (PL) spectra of the CQDs. On the basis of the obtained results from the XPS and PL measurements, we propose a mechanism in understanding and explaining the photon-induced light emission from CQDs. This study is relevant to the fabrication and application of fluorescent CQDs as, e.g., light display materials.