Changmin Hou

Porous carbon-coated cobalt sulfide nanocomposites derived from metal organic frameworks (MOFs) as an advanced oxygen reduction electrocatalyst

Porous carbon-coated CoS1.097 nanocomposites (PC-CoS1.097 NCs) were synthesized by a one-step controlled pyrolysis of the zeolitic imidazolate framework ZIF-9 with sulfur powder. The resulting porous composites contained a high level of nanoparticles of CoS1.097 and exhibited considerable mesoporosity. With remarkable electrocatalytic activity, the nanocomposites provided a four-electron pathway for the oxygen reduction reaction (ORR) in alkaline medium. The advantages of the synthesized composites over commercial Pt/C include a high methanol crossover resistance and superior long-term stability lasting for 10 000 s cycles. The cost-effective, stable and highly active PC-CoS1.097 NC electrodes have great potential for application in direct methanol fuel cells (DMFCs). This study lays a foundation for the future development of new cost-effective electrocatalysts.

Hydrothermal synthesis and magnetic properties of REFe0.5Cr0.5O3 (RE = La, Tb, Ho, Er, Yb, Lu and Y) perovskite

A low temperature, one-pot route to iron-doped rare-earth chromite perovskite was proposed. Fe half-doped rare-earth chromites, REFe0.5Cr0.5O3 (RE = La, Tb, Ho, Er, Yb, Lu and Y) were prepared via a mild hydrothermal method and their magnetic properties were studied. All of these materials are well-crystallized and the profile refinement of powder X-ray diffraction (XRD) data showed that each of them adopts an orthorhombic distorted (Pbnm) perovskite structure. The temperature dependence of the magnetization curves indicate an improved order of arrangement of Fe3+ and Cr3+ at the B-site in some samples. Hysteresis measurements of YFe0.5Cr0.5O3 indicate that saturated and remnant magnetization were improved greatly compared to that prepared via the solid state method.

Electrochromic response of pulsed laser deposition prepared WO3–TiO2 composite film

Electrochromic films of WO3 with varying content of TiO2, as a composite, were prepared via pulsed laser deposition method. The composite films exhibited cathodic electrochromism, which changed the original colorless appearance to a deep blue color. The films were examined for their structure, morphology, ultraviolet to visible photon absorption and chromic changes in electric fields. Pure WO3 film showed stronger absorption at 600–800 nm wavelength of light than the composite films, which corresponds to blue color. The most intensive absorption wavelength of light could be modulated with TiO2 inclusion, leading to a respective color change from dark blue to gem blue of the as-deposited WO3–TiO2–ITO glass. This work may serve as a basis for electrochromic windows and display device applications.

Hydrothermal synthesis, influencing factors and excellent photocatalytic performance of novel nanoparticle-assembled Bi25FeO40 tetrahedrons

Novel nanoparticle-assembled Bi25FeO40 (BFO) tetrahedrons with relatively good dispersion were successfully synthesized through a facile, mild and rapid hydrothermal process. The phases and morphologies of the samples were characterized by powder X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). Such sillenite-type BFO tetrahedrons were found to be fabricated by abundant nanoparticles with single crystalline nature. Some influencing factors including reaction time, temperature and the amount of additives (e.g., polyacrylamide, sodium citrate and sodium hydroxide) were revealed to play crucial roles in the generation of this BFO nanoarchitecture. Moreover, the visible light-driven photocatalytic activities of the BFO products were investigated.

Novel Bi12ZnO20–Bi2WO6 heterostructures: facile synthesis and excellent visible-light-driven photocatalytic activities

Novel sillenite-type Bi12ZnO20–Bi2WO6 heterostructure photocatalysts were successfully prepared via a controllable partial precipitate conversion strategy, employing previously-prepared Bi2WO6 nanosheets as precursors of Bi3+. The phases and morphologies of the products were characterized by powder X-ray diffraction, energy dispersive spectrometry, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and scanning electron microscopy. Compared to the sample (Bi12ZnO20 + Bi2WO6) obtained by physical mixing technology and the single-component photocatalyst (Bi12ZnO20 and Bi2WO6), such sillenite-type Bi12ZnO20–Bi2WO6 heterostructures exhibited higher visible-light-driven photocatalytic activity, which could be ascribed to matching band positions and intimate interfacial contact between different components that could benefit the efficient separation of photo-generated carriers.

Morphology-controllable synthesis of novel Bi25VO40 microcubes: optical properties and catalytic activities for the reduction of aromatic nitro compounds

In the present paper, novel Bi25VO40 microcubes with relatively good dispersion have been fabricated via a facile, fast and mild hydrothermal synthesis strategy. The morphology and compositional characteristics of the Bi25VO40 sample were characterized by various testing techniques including powder X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), FT-IR spectroscopy, energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). Several experimental parameters including synthesis temperature, time and the amount of additives (e.g., polyacrylamide, sodium citrate and sodium hydroxide) were discovered to play vital roles in the construction of these Bi25VO40 microcrystals. From the UV-vis diffuse reflectance spectrum (DRS) of the Bi25VO40 its band gap was calculated to be 2.42 eV. The photoluminescence (PL) spectrum showed that Bi25VO40 microcubes had two obvious emission peaks centered at 458 and 639 nm. Moreover, catalytic experiments showed that the as-prepared Bi25VO40 microcubes possessed superior catalytic performance for the conversion of 4-nitrophenol (4-NP) and 4-nitroaniline (4-NA) in the presence of excess NaBH4 solution.

Fabrication of TiO2 hollow nanocrystals through the nanoscale Kirkendall effect for lithium-ion batteries and photocatalysis

TiO2 hollow structures have important applications in high performance lithium ion batteries and efficient photocatalysis. In contrast to the conventional synthesis routes where various soft or hard templates are usually put into use, the direct growth of uniform TiO2 hollow nanocrystals is presented. The growth mechanism, lithium ion battery performance, and photocatalytic activity of the resultant TiO2 hollow nanocrystals are thoroughly investigated. TiO2 hollow nanocrystals can be synthesized through a mechanism analogous to the nanoscale Kirkendall effect. The hollow structure results in highly active photocatalysis, high rate capability, and stable cycling.

Structural and Optical Properties of ZnO Films with Different Thicknesses Grown on Sapphire by MOCVD

ZnO (002) films with different thicknesses, grown on Al2O3 (006) substrates by metal-organic chemical vapor deposition (MOCVD), were etched by Ar ion beams. The samples were examined by D8 X-ray diffraction, scanning electron microscopy (SEM), and photoluminescence (PL) spectrometry. The structural properties vary with the increasing thickness of the films. When the film thickness is thin, the phi (Φ) scanning curves for ZnO(103) and sapphire(116) substrate show the existence of two kinds of orientation relationships between ZnO films and sapphire, which are ZnO (002) // Al2O3 (006), ZnO (100) // Al2O3 (110) and ZnO (002)// Al2O3 (006), ZnO (110)//Al2O3 (110). When the thickness increases to 500 nm there is only one orientation relationship, which is ZnO (002)// Al2O3 (006), ZnO [100]// Al2O3 [110]. Their photoluminescence (PL) spectra at room temperature show that the optical properties of ZnO films have been greatly improved when increasing the thickness of films is increased.

Crystal facet control of LaFeO3, LaCrO3, and La0.75Sr0.25MnO3

By changing the traditional hydrothermal environment, facets of LaFeO3, La0.75Sr0.25MnO3, and LaCrO3 can be tailored from low energy {100} facets to {110}, {111}, and a mixture of them, respectively.

The effect of NH4+ on shape modulation of La1−xSrxMnO3 crystals in a hydrothermal environment

Perovskite oxide (La1−xSrxMnO3) crystal facet control is rarely reported due to difficulties in modulation, even though it is highly important in surface-dependent catalytic and electrochemical applications. In this paper, we present the shape diversity of La1−xSrxMnO3 crystals evolved from a hydrothermal environment when urea is used as an effective facet modulator. By changing the La/Sr ratio from 1 to 3, the structure changes from pseudo-cubic to P21/a monoclinic, induced by the evolution processes of different facets during crystallization. Our proposed hypothesis is that the NH4+ interaction with octahedral MnO6 may be beneficial in enhancing the activity of La1−xSrxMnO3 for applications, and moves toward strategies for the development of highly active perovskite oxides.