Wenxia Yuan

Enhanced photocatalytic H2 evolution over micro-SiC by coupling with CdS under visible light irradiation

The rate of visible-light-driven photocatalytic hydrogen production from water splitting is greatly enhanced from zero to 555 μmol h−1 g−1 through hybridizing a suitable amount of CdS particles onto the micro-SiC surface. It suggests that the hybridization is responsible for lowering the surface activation energy of SiC and well-connected SiC/CdS interfaces serve as active sites for photocatalytic reactions, leading to this significant enhancement. The self-corrosion of CdS is simultaneously avoided and the composites show high stability. Our results demonstrate that SiC powder with high electron mobility, low cost, availability of large amounts and environmental friendliness has potential to become an efficient catalyst that might find practical applications.

Photocatalytic water splitting to hydrogen production of reduced graphene oxide/SiC under visible light

We report a method to realize the H2 production and graphene-oxide (GO) reduction simultaneously over GO/SiC composite under visible light irradiation with KI as sacrifice reagent. The weight content of GO is regulated in the reaction system. The rate of H2 production reaches to 95u2009μL/h with 1% GO content in GO/SiC composite system, which is 1.3 times larger compared to the case in pure SiC NPs under visible light. The reduced-GO sheet can serve as an electron collector and transporter to efficiently separate the photo-generated electron-hole pairs, lengthening the lifetime of the charge carriers effectively.

Preparation of single- and few-layer graphene sheets using co deposition on SiC substrate

Single- and few-layer graphene sheets were fabricated by selective chemical reactions between Co film and SiC substrate. A rapid cooling process was employed. The number of layers and crystallinity of graphene sheets were controlled by process parameters. The formation mechanism of graphene was highly sensitive to carbon diffusion. Free carbon precipitated and then moved across the product layer that was composed mainly of cobalt-silicides. The graphene layer formed homogeneously on the surface and then transferred to the other substrate. This could provide a method for high-quality fabrication of wafer-sized graphene sheets.

Syntheses and crystal structures of trigonal rare-earth dioxymonocyanamides, Ln(2)O(2)CN(2) (Ln = Dy, Ho, Er, Tm, Yb)

Trigonal rare-earth dioxymonocyanamides Ln(2)O(2)CN(2) (Ln=Dy,Ho,Er,Tm,Yb) were synthesized by the modified solid-state metathesis (SSM) method, in which Ln(2)O(3) and melamine C3N6H6 were mixed and heated at 850 degrees C in vacuumed silica ampoules. Possible chemical reaction pathways are proposed. X-ray diffraction (XRD) patterns of Ln(2)O(2)CN(2) were refined using the Rietveld method. Compounds Ln(2)O(2)CN(2) crystallize in the trigonal system with space group P(3) over bar m1, Z=1, and cell parameters of a and c varying from 3.7267(1) to 3.6407(1) angstrom and from 8.1848(3) to 8.1152(3) angstrom, respectively, as Ln atoms change from Dy to Yb. These compounds have stacking structures of Ln(2)O(2)(2+) and CN22- layers, similar to those of previously reported compounds Ln(2)O(2)CN(2) (Ln = Ce, Pr, Nd, Sm, Eu, Gd). The presence of CN22- ions has been confirmed by infrared spectroscopy, with two characteristic peaks in the vicinity of 651 and 2075 cm(-1)

Investigation of Ta/Ni bilayered ohmic contacts on n-type SiC single-crystal substrate

The interfacial reactions between a Ta/Ni bilayered film and SiC single-crystal substrate during annealing at 650–1,100xa0°C were investigated. It was found that H-Ni2Si (hexagonal Ni2Si) and TaC formed at the interface as a result of thermal annealing. A small amount of free C atoms diffused outwards the surface, leading to the formation of carbon vacancies that could act as electron donors. The electrical properties of the contacts showed that ohmic behavior was observed for the sample annealed above 800xa0°C. The specific contact resistivity was determined to be as low as 4.4xa0×xa010−4xa0Ωxa0cm2 at 1,100xa0°C.Graphical abstract

Synthesis and structure of the ternary nitride Li6WN4

The ternary nitridotungstate Li6WN4 has been synthesized via the solid state reaction of lithium subnitride, Li3N, with W under nitrogen. High quality X-ray powder diffraction data were collected for the crystal-structure determination. Li6WN4 crystallizes in the tetragonal system, space group P4(2)/nmc, with cell parameters a = 6.6759(3) angstrom and c = 4.9280(3) angstrom, Z = 2. Preliminary thermal stability measurements of Li6WN4 show that it is sensitive to moisture, even at room temperature, and decomposes at high temperatures below 1000 degrees C under flowing nitrogen. (c) 2005 International Centre for Diffraction Data.

Investigation on solid solubility and magnetism of the non-stoichiometric compound Fe3Se4

In order to complete the research on the Fe-Se binary system, the phase structures with selenium contents from 50 to 60 at.% have been studied. Fe-Se binary samples used in this study were prepared by the high-temperature solid-state reaction method, and the phase structure of each sample was determined by powder X-ray diffraction. The solid solubility of the Fe3Se4 phase was determined to be from 56.1 to 57.6 at.% Se based on the values of unit-cell parameters. Magnetic properties of the samples were also studied

Erratum: “Photocatalytic water splitting to hydrogen production of reduced graphene oxide/SiC under visible light” [Appl. Phys. Lett. 102, 083101 (2013)]

(1) Department of Chemistry, School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing 100083, China

Chemical reactions in the Co-Si-C system

K2Zn3(P2O7)(2) was synthesized by solid state reaction and its crystal structure was determined by ab initio method from powder X-ray diffraction (XRD) data. The title compound was determined to be orthorhombic with space group P2(1)2(1)2(1), Z=4, and lattice parameters a=12.901(8) angstrom, b=10.102(6) angstrom, and c=9.958(1) angstrom. Values of lattice parameters from 303 to 573 K were measured by temperature-dependent XRD. Thermal expansion coefficients alpha(0), lattice parameters, and cell volume at 0 K were determined to be alpha(0)(a)=1.62327X 10(-4)/K, a(0)=12.855(4) angstrom, alpha(0)(b) = 1.17921 X 10(-4)/K, b(0)=10.070(8) angstrom, alpha(0)(c)=2.62364X 10(-4)/K, c(0)=9.880(4) angstrom, and alpha(0)(V) = 6.599 X 10(-2) /K, V-0 = 1278.967(0) angstrom(3). The specific heat equation as a function of temperature was determined to be C-p=0.77115 +0.00231 T-1241.60027T(-2)- 1.4133 X 10(-6)T(2) (J/K g), for temperatures from 198 to 710 K. The melting point estimated from the mu-DTA heating curve is 795 degrees C

Homogeneous dispersion of high-conductive reduced graphene oxide sheets for polymethylmethacrylate nanocomposites

The high cohesive interaction between reduced graphene oxide (RGO) sheets usually makes them difficult to disperse, which limits their utilization in achieving effective hybridization with polymers. We report here a new two-step route for preparing non-aggregated and high-conductive RGO powders. Graphene oxide precursor was first reduced by hydrazine hydrate in presence of a thermal unstable surfactant of cetyltrimethylammonium chloride (CTAC). Then a thermal annealing process under H 2 /Ar atmosphere was further used to remove the non-conductive CTAC molecules. The prepared RGO powder exhibited an electrical conductivity of 2.23xa0×xa010 4 xa0Sxa0m −1 – about ten times higher than the one (N-RGO) simply reduced by hydrazine hydrate. After incorporating into polymethylmethacrylate with a 5xa0wt% loading, the composite showed a conductivity of 4.11xa0Sxa0m −1 , which was 60 times as high as that of the same composite based on N-RGO powder. The addition and subsequent removal of CTAC molecules is an effective method for preparing non-aggregated and highly conductive graphene powder and obtaining good incorporation into polymer matrices.