Zhongnan Guo

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.

High-efficient photo-electron transport channel in SiC constructed by depositing cocatalysts selectively on specific surface sites for visible-light H2 production

Control cocatalyst location on a metal-free semiconductor to promote surface charge transfer for decreasing the electron-hole recombination is crucial for enhancing solar energy conversion. Based on the findings that some metals have an affinity for bonding with the specific atoms of polar semiconductors at a heterostructure interface, we herein control Pt deposition selectively on the Si sites of a micro-SiC photocatalyst surface via in-situ photo-depositing. The Pt-Si bond forming on the interface constructs an excellent channel, which is responsible for accelerating photo-electron transfer from SiC to Pt and then reducing water under visible-light. The hydrogen production is enhanced by two orders of magnitude higher than that of bare SiC, and 2.5 times higher than that of random-depositing nano-Pt with the same loading amount.

Heterogeneous nucleation of CdS to enhance visible-light photocatalytic hydrogen evolution of SiC/CdS composite

Synthesis of composite photocatalyst is one of the most important strategies to enhance the yield of hydrogen produced by water splitting. However, one photocatalyst usually tends to randomly aggregate on the others surface, which weakens the electron transport of the heterogeneous interface. Herein, we developed a hydrothermal reaction to synthesize the SiC/CdS composite with a feasible Z-scheme and well-controlled dispersion of CdS on SiC surface. Heterogeneous structure on the catalyst interface is obtained, leading to more light-absorption and effective electron-hole separation between the well-contacted components, which contribute to the doubly enhanced photocatalytic performance of the composite. This work provides a simple and practical route to improve the catalytic activity by optimizing the intrinsic contact of Z-scheme composite semiconductors.

Kx(C2H8N2)yFe2−zS2: synthesis, phase structure and correlation between K+ intercalation and Fe depletion

We report a new layered FeS compound Kx(C2H8N2)yFe2−zS2 synthesized by intercalating K and C2H8N2 into tetragonal FeS via a simple sonochemical route. This new compound crystallizes in a body-centered tetragonal unit cell, with the [K(C2H8N2)] and [FeS] layers alternately stacking along the c direction. The nominal concentration of K, x, can be adjusted from 0.25 to 0.45, and the lattices a and c contract from 3.6971(9) and 20.667(5) A to 3.691(1) and 20.566(7) A, respectively. When x 0.45, K reacts with FeS directly to form K2Fe4S5 impurity. It is found that the C2H8N2 molecule has been co-intercalated in between the [FeS] layers along with K, evidenced by its content, y, having a linear dependence with x. Measurements indicate that Kx(C2H8N2)yFe2−zS2 is a semiconductor and it shows a weak ferrimagnetism below 50 K. More importantly, Fe depletion resulting from the charged K+ intercalation was revealed by composition analysis, which leads to the formation of disordered Fe vacancies in the [FeS] layers and hence hinders the enhancement of original superconductivity in the FeS parent.

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

Density and surface tension of liquid Bi–Cu–Sn alloys

The surface tension and density of the ternary Bi–Cu–Sn alloys have been measured by the sessile-drop method. Measurements were carried out for three cross sections with the constant bismuth-to-copper ratios of 2:1, 1:1, and 1:2. The density of all the investigated alloys decreases with rising temperature. A decrease of the surface tension is also observed when the temperature increases, except at two compositions on the copper-rich side. An increase of copper content could slightly decrease the density in the Bi–Cu–Sn system and significantly increase the surface tension as well. Experimental values of the surface tension were also compared with those calculated from Butler’s equation.Graphical Abstract

Cs0.9Ni3.1Se3: A Ni-Based Quasi-One-Dimensional Conductor with Spin-Glass Behavior

In this work, we report the discovery of a new Ni-based quasi-one-dimensional selenide: Cs0.9Ni3.1Se3. This compound adopts the TlFe3Te3-type structure with space group P63/ m, which consists of infinite [Ni3Se3] chains with face-sharing Ni6 octahedra along the c direction. The lattice parameters are calculated as a = 9.26301(4) Å and c = 4.34272(2) Å, with the Ni-Ni distance in the ab plane as 2.582(3) Å, suggesting the formation of a Ni-Ni metallic bond in this compound. Interestingly, it has been found that Cs0.9Ni3.1Se3 is nonstoichiometric, which is different from the other TlFe3Te3-type phases reported so far. Structure refinement shows that the extra Ni atom in the structure may occupy the 2c site, together with Cs atoms. Cs0.9Ni3.1Se3 shows metallic behavior with monotonously decreased resistivity with temperatures from 300 to 0.5 K. Measurements on the magnetic susceptibility display a spin-glass state below 7 K. The specific heat curve gives a Sommerfeld coefficient of 14.6 mJ·K-2·mol-1 and a Debye temperature of 143.6 K. The discovery of this new compound enriches the diversity of low-dimensional materials in a transition-metal-based family and also sheds light on the structure-property relationship of this system.

Different effect of quenching temperature on Fe1+σTe0.5Se0.5 and β-FeSe

In this work, we have demonstrated a different effect on Fe1+σTe0.5Se0.5 and β-FeSe by changing the quenching temperature. Tc is clearly reduced in Fe1+σTe0.5Se0.5 after increasing the quenching temperature from 300 °C to 500 °C, while that of β-FeSe is almost unchanged. Structure refinement indicates that after quenched at 500 °C, FeTe4 tetrahedron exhibits an expansion with the stretched Fe-Te bond, together with the increased amount of interstitial iron. These particular changes on structure are believed to be responsible for the suppression of superconductivity in Fe1+σTe0.5Se0.5.