Mingxia Li

Phosphorus‐Doped Carbon Nitride Tubes with a Layered Micro‐nanostructure for Enhanced Visible‐Light Photocatalytic Hydrogen Evolution

Phosphorus-doped hexagonal tubular carbon nitride (P-TCN) with the layered stacking structure was obtained from a hexagonal rod-like single crystal supramolecular precursor (monoclinic, C2/m). The production process of P-TCN involves two steps: 1) the precursor was prepared by self-assembly of melamine with cyanuric acid from in situ hydrolysis of melamine under phosphorous acid-assisted hydrothermal conditions; 2) the pyrolysis was initiated at the center of precursor under heating, thus giving the hexagonal P-TCN. The tubular structure favors the enhancement of light scattering and active sites. Meanwhile, the introduction of phosphorus leads to a narrow band gap and increased electric conductivity. Thus, the P-TCN exhibited a high hydrogen evolution rate of 67 μmol h(-1) (0.1 g catalyst, λ >420 nm) in the presence of sacrificial agents, and an apparent quantum efficiency of 5.68 % at 420 nm, which is better than most of bulk g-C3 N4 reported.

Fabrication of noncovalently functionalized brick-like β-cyclodextrins/graphene composite dispersions with favorable stability

Noncovalently functionalized β-cyclodextrins (β-CDs)/graphene composite dispersions have been fabricated through layer-by-layer self-assembly. Scanning electron microscope and transmission electron microscopy characterization confirm that the β-CDs/graphene composites possess brick-like sandwich-type structure. X-ray diffraction results illustrate that β-CDs covering on the surface of graphene possess channel-type structures. Moreover, the obtained β-CDs/graphene composites exhibit good dispersibility in common polar solvents and could exist for several weeks. In particular, the composites could be dispersed well in water at concentrations up to 2 mg mL−1 and stably exist at pH values from 4 to 12. The facts indicate that there exist certain forces between graphene and β-CDs. In order to clarify the interaction between them, we adopt a molecular mechanics (MM) method to evaluate the driving force. According to MM simulations, van der Waals forces should be the driving force for the formation of the well-defined β-CDs/graphene composites, and hydrogen-bonding interaction between adjacent β-CD molecules is another driving force for the formation of this stable graphene dispersion, which is similar to that of the β-CDs/carbon nanotubes composite. But the binding energy of the β-CDs/graphene composite is larger than that of the latter, suggesting much stronger interaction between graphene and β-CD molecules due to the two-dimensional flat-structure of graphene offering more and efficient sites to interact with β-CD molecules compared to carbon nanotubes with large interfacial curvature. These theoretical data for the existence of these interactions are further confirmed by experimental results from Raman and thermogravimetric analysis-differential scanning calorimetry.

Large-scale synthesis of stable mesoporous black TiO2 nanosheets for efficient solar-driven photocatalytic hydrogen evolution via an earth-abundant low-cost biotemplate

Stable mesoporous black anatase TiO2 nanosheets (MBTNs) are synthesized via an earth-abundant low-cost biotemplate method combined with an ethanediamine encircling process, and subsequent high-temperature calcinations and surface hydrogenation. The MBTNs, which can be synthesized on a large scale with a low cost, are composed of Ti3+ in frameworks and surface disorders. In this case, the employment of ethanediamine encircling plays a vital role in fabricating the stable MBTNs, and not only favors high-temperature hydrogenation (600 °C), but also retains the mesoporous network as well as inhibiting the anatase-to-rutile phase transformation and grain growth. The resultant MBTNs possess a relatively high surface area of ∼74 m2 g−1, and large pore size and pore volume of ∼10 nm and 0.15 cm3 g−1, respectively. The MBTNs, with a narrow bandgap of ∼2.85 eV, can extend the photoresponse from the ultraviolet to visible light region, and exhibit an excellent solar-driven photocatalytic hydrogen evolution rate (∼165 μmol h−1 0.05 g−1), which is about twice as high as that of pristine mesoporous TiO2 nanosheets (∼82 μmol h−1 0.05 g−1). This efficient solar-driven photocatalytic hydrogen evolution is ascribed to the synergistic effects of the highly crystalline, ultrathin 2D mesoporous structure of Ti3+ in frameworks and surface disorders.

The fabrication and the characterization of a TiO2/titanate nanohybrid for efficient hydrogen evolution

A TiO2/titanate nanojunction photocatalyst was synthesized by a one-step hydrothermal process. Scanning electron microscopy and transmission electron microscopy were employed to characterize the morphology and structure, and to further elucidate the morphological evolution of the resulting products. X-ray diffraction and X-ray photoelectron spectroscopy were used to generally assess the crystallite phase composition of the samples and the phase transition behaviour. The TiO2/titanate nanojunction with excellent structure is of benefit for mass transfer and especially for photon-generated electron–hole separation. As a result, the nanojunction is anticipated to exhibit good photocatalytic activities for hydrogen evolution. The H2 evolution of TiO2/titanate achieves a production rate of 230.1 μmol h−1. Moreover, this report will offer a new promising strategy to improve photocatalytic hydrogen evolution efficiency with low-cost.

In situ synthesis, enhanced luminescence and application in dye sensitized solar cells of Y 2 O 3 /Y 2 O 2 S:Eu 3+ nanocomposites by reduction of Y 2 O 3 :Eu 3+

Y2O3/Y2O2S:Eu3+ nanocomposites were successfully prepared by reducing Y2O3:Eu3+ nanocrystals. The obtained Y2O3/Y2O2S:Eu3+ nanocomposites not only can emit enhanced red luminescence excited at 338 nm, but also can be used to improve the efficiency of the dye sensitized solar cells, resulting an efficiency of 8.38%, which is a noticeable enhancement of 12% compared to the cell without Y2O3/Y2O2S:Eu3+ nanocomposites. The results of the incident photon to current, dynamic light scattering, and diffuse reflectance spectra indicated that the enhancement of the cell efficiency was mainly related to the light scattering effect of Y2O3/Y2O2S:Eu3+ nanocomposites. As a phosphor powder, the emission at ~615 nm of Y2O3/Y2O2S:Eu3+ was split into two sub-bands. Compared with Y2O3:Eu3+, the 5D0 → 7F0 and 5D0 → 7F1 emissions of Y2O3/Y2O2S:Eu3+ showed a little red-shift.

A New Combustion Route to Synthesize Mixed Valence Vanadium Oxide Heterojunction Composites as Visible-Light-Driven Photocatalysts

The fabrication of a semiconductor heterojunction photocatalyst is a key aim of the visible light photocatalytic field owing to its central role in the enhancement of photogenerated charge separation and quantum efficiency. Herein, a new mixed valence vanadium oxide composite with the VO2@V6O13 heterojunction is fabricated through the facile and direct combustion of an ethanol solution composed of ammonium metavanadate and diethyl imidazole. XRD and TEM analyses reveal the structural evolution at the interface between VO2 and V6O13, which manipulates the electronic structure of the composites. The composition and chemical state of the composites are obtained by using X‐ray photoelectron spectroscopy. In addition, the detailed energy band structure has been confirmed by the analysis of the UV/Vis absorption spectra and X‐ray photoelectron spectroscopy valence band spectra. The mixed valence vanadium oxides readily narrow their energy gap (1.4–2.5 eV), which enables the efficient utilization of visible light and the improvement in charge separation rate. Thus, the photocatalysts with the VO2@V6O13 heterojunction demonstrate improved photocatalytic activity and structural stability in the degradation of atrazine pesticide under visible light irradiation, which is an effective solution for the problem of remnant pesticides for future agriculture. Furthermore, this facile and straightforward method has promising applications in the fabrication of other heterostructure photocatalysts.