Kai Dai

Composition dependent metal-semiconductor transition in transparent and conductive La-doped BaSnO3 epitaxial films

Perovskite-structured (LaxBa1−x)SnO3 (x = 0–0.20) (LBSO) films were epitaxially grown on MgO substrates by pulsed laser deposition, and the structural, electrical, and optical properties of the films were investigated. Results show that these films exhibit a high transmittance of more than 90% in the visible region and dopant concentration-dependent metal-semiconductor transition (MST). With increasing La content from 0 to 0.20 in LBSO films, the MST temperatures decrease from 105 to 32 K and then increase again regularly. The semiconducting behaviors at low temperatures of the films with different La doping concentrations were explained by two different conductive models based on weak localization and Anderson localization.

Z-机制磷酸银/钨酸铋复合物的构建及其可见光催化降解有机污染物

Abstract Ag3PO4 has good potential for use in photocatalytic degradation of organic contaminants. However, the activity and stability of Ag3PO4 is hard to sustain because of photocorrosion and the positive potential of the conduction band of Ag3PO4. In this study, A composite consisting of Bi2WO6 nanosheets and Ag3PO4 was developed to curb recombination of charge carriers and enhance the activity and stability of the catalyst. Formation of a Ag3PO4/Bi2WO6 composite was confirmed using X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Photoluminescence spectroscopy provided convincing evidence that compositing Bi2WO6 with Ag3PO4 effectively reduced photocorrosion of Ag3PO4. The Ag3PO4/Bi2WO6 composite gave a high photocatalytic performance in photodegradation of methylene blue. A degradation rate of 0.61 min−1 was achieved; this is 1.3 and 6.0 times higher than those achieved using Ag3PO4 (0.47 min−1) and Bi2WO6 (0.10 min−1), respectively. Reactive species trapping experiments using the Ag3PO4/Bi2WO6 composite showed that holes, ·OH, and ·O2− all played specific roles in the photodegradation process. The photocatalytic mechanism was investigated and a Z-scheme was proposed as a plausible mechanism.

Structure and band gap tuning of transparent (Ba1-xSrx)SnO3 thin films epitaxially grown on MgO substrates

(Ba1-xSrx)SnO3 (x=0–1) (BSSO) films were epitaxially grown on MgO substrates by pulsed laser deposition. X-ray diffraction, atomic force microcopy, and optical transmittance investigations reveal that the lattice and band structure properties of the BSSO films can be modified significantly by changing the Sr content. With increasing Sr content from 0 to 1 in films, the lattice parameters decrease from 4.123 to 4.037 A gradually, while the optical band gaps energy increases from 3.50 to 4.27 eV linearly, which was attributed to the octahedral tilting distortion pushing up the minimum of conduction band. This large structure and band gap tuning of BSSO films are promising for desired applications in the thin-film architecture.

Facile synthesis of a reduced graphene oxide/cobalt sulfide hybrid and its electrochemical capacitance performance

In this work, reduced graphene oxide (RGO) in situ composites with cobalt sulfide (CoS) are achieved through a facile hydrothermal approach. The morphology and structure of the composite materials have been investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and X-ray diffraction (XRD). The results have shown that the composites consist of CoS nanoparticles with a diameter of 30–50 nm uniformly dispersed on the basal plane of RGO. The maximum specific capacitance of 1130 F g−1 measured by chronopotentiometry at a current density of 0.5 A g−1 is obtained in a 6 M KOH aqueous solution, which is 2.4 times higher than that of pure CoS nanoparticle electrodes (473 F g−1). Furthermore, RGO/CoS nanocomposite exhibits good cycling stability with 92.1% capacitance retention over 1000 cycles.

Construction of organic–inorganic cadmium sulfide/diethylenetriamine hybrids for efficient photocatalytic hydrogen production

The design and control of effective, sustainable, cheap, and reusable photocatalysts are crucial to the development of solar energy conversion to hydrogen (H2) for solving environmental problems. The cadmium sulfide/diethylenetriamine (CdS/DETA) hybrid in a single crystalline structure was achieved by a solvothermal approach. The organic-inorganic CdS/DETA hybrid shows high performance and satisfactory stability for H2 production under visible-light irradiation. The synergetic chemical coupling effect between CdS and DETA leads to a marked increase in the H2 generation rate and the apparent quantum yield. H2-production rate of CdS/DETA24 under visible light illumination are 31.7% and 8059.5μmolg-1h-1, respectively, which is 3.5 times more than CdS nanorods without DETA. Our findings may give a promising method to improve CdS for efficient electron-hole separation, electron transferring and anticorrosion in photocatalytic process, which reforms the conventional organic-inorganic hybrid system.

Advance ternary surface-fluorinated TiO2 nanosheet/Ag3PO4/Ag composite photocatalyst with planar heterojunction and island Ag electron capture center

Morphology, phase structure and optical performance of ternary surface-fluorinated TiO2 nanosheet/Ag3PO4/Ag composite photocatalysts were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectroscopy (DRS). Wide band-gap TiO2 crystal nanosheets were synthesized while stabilizing the {001} facet, which is highly active for oxidation reactions, with fluorination. Narrow band-gap Ag3PO4 crystal was then uniformly grown on a fluorinated-TiO2 nanosheet {001} facet, forming a planar heterojunction between two nanosheet semiconductors. Ag particles were in situ reduced by visible light irradiation from Ag3PO4, forming island-distributed Ag on the Ag3PO4 surface. TiO2/Ag3PO4/Ag exhibited excellent photocatalytic activity and high stability for methylene blue degradation under 410 nm LED light irradiation. The enhanced activities of TiO2/Ag3PO4/Ag could be attributed to effective electron–hole separation, fast hole transportation and the Schottky barrier. This novel ternary TiO2/Ag3PO4/Ag structure material is an ideal candidate in environmental treatment and cleaning applications.

Green synthesis of monodispersed LaCO3OH microgears with novel plum blossom-like structure via a glycerol-mediated solvothermal method

Monodispersed LaCO3OH microgears with a novel plum blossom-like structure are prepared by a simple, reliable, environmentally-friendly and glycerol-mediated solvothermal method for the first time. By studying the effect of the experimental parameters on the morphology of LaCO3OH structures, we find that urea and glycerol at high concentration play a significant role in the formation of the plum blossom-like LaCO3OH microgears. In addition, we observe that the morphology evolution of the LaCO3OH microgears is from wires, spheres composed of rods, to plum blossom-like products with the increase of reaction time. More importantly, PL results demonstrate that the LaCO3OH microgears show a stronger PL than that of other structures, such as wires and spheres.

A facile and novel approach for preparing monodispersed hollow aluminosilica microspheres with thin shell structures

Monodispersed hollow aluminosilica microspheres (HAMs) with thin shell structures have been successfully synthesized via a novel method. The facile strategy is simple, efficient, and highly controllable. A NaAlO2 aqueous solution is firstly employed as an alkaline solution to directly etch silica microspheres hard templates without additional surfactants to form monodispersed hollow microspheres. On the basis of the proposed formation mechanism of etching followed by co-assembly, the size of HAMs is fully dependent on the size of silica sphere hard templates.

Composition dependence of structural and optical properties in epitaxial Sr(Sn1?xTix)O3 films

Epitaxial Sr(Sn1?xTix)O3 (SSTO, x = 0?1) thin films were grown on MgO substrates by a pulsed laser deposition technique. The effects of composition on the structural and optical properties of SSTO films were investigated. X-ray diffraction studies show that the lattice parameter decreases from 4.041 to 3.919 ? gradually with increasing Ti content from 0 to 1 in SSTO films. Optical spectra analysis reveals that the band gap energy Eg decreases continuously from 4.44 to 3.78 eV over the entire doping range, which is explained by the decreasing degree of octahedral tilting distortion and thus the increasing tolerance factor caused by the increasing small-Ti-ion doping concentration.

Morphology dependent adsorption of methylene blue on trititanate nanoplates and nanotubes prepared by the hydrothermal treatment of TiO2

The adsorption properties of two nanomorphologies of trititanate, nanotubes (TiNT) and plates (TiNP), prepared by the hydrothermal reaction of concentrated NaOH with different phases of TiO2, were examined. It was found that the capacity for both morphologies towards methylene blue (MB), an ideal pollutant, was extremely high, with the TiNP having a capacity of 130 mg/g, higher than the TiNT, whose capacity was 120 mg/g at 10 mg/L MB concentration. At capacity, the well-dispersed powders deposit on the floor of the reaction vessel. The two morphologies had very different structural and adsorption properties. TiNT with high surface area and pore volume exhibited exothermic monolayer adsorption of MB. TiNP with low surface area and pore volume yielded a higher adsorption capacity through endothermic multilayer adsorption governed by pore diffusion. TiNP exhibited a higher negative surface charge of -23 mV, compared to -12 mV for TiNT. The adsorption process appears to be an electrostatic interaction, with the cationic dye attracted more strongly to the nanoplates, resulting in a higher adsorption capacity and different adsorption modes. We believe this simple, low cost production of high capacity nanostructured adsorbent material has potential uses in wastewater treatment.