Indirect-direct band transformation of few-layer BiOCl under biaxial strain

Being a new two-dimensional layered compounds, the tunable indirect-direct band transformation of BiOCl with different layers can be realized by introducing the biaxial tensile or compressive strains. The band structure and stability of BiOCl with different layers are first researched to clarify the influence of layer numbers. A phase transformation of bilayer BiOCl and metallic characteristic for all are observed under large tensile and compressive strains, respectively. In addition, bond length, interlayer spacing, and band decomposed charge density are calculated to analyze the mechanism behind these phenomena. The results indicate that the band structure transformation is primarily related to the competitions between two kinds of intralayer and interlayer Bi-O bonds and hybridizations between atoms under strains

Magnetic properties and microstructures of iron oxide@mesoporous silica core-shell composite for applications in magnetic dye separation

In this report, hollow mesoporous silica (HMS) and iron oxide-hollow mesoporous silica (FexOy@HMS) core-shell composite were prepared by a one-step facile fabrication method. Transmission electron microscopy, X-ray diffraction, N-2 adsorption-desorption isotherms, and vibrating sample magnetometer were used to characterize the morphology, microstructure, and magnetic properties of the HMS and core-shell composite. The magnetic separability of FexOy@HMS core-shell composite was tested in Rhodamine B (Rh. B) dye solution. The results indicate that the core-shell composite can absorb Rh. B dyes molecules effectively up to 90.1%. (C) 2012 American Institute of Physics. [doi:10.1063/1.3670049

Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing

Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H2/Ar atmosphere with different H2/Ar ratios. It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO. Mn ions initially enter into interstitial sites and a Mn3+O6 octahedral coordination is produced in the prepared Mn-doped ZnO sample, in which the nearest neighbor Mn3+ and O2 ions could form a Mn3+-O2--Mn3+ complex. After H2 annealing, interstitial Mn ions can substitute for Zn to generate the Mn2+O4 tetrahedral coordination in the nanocrystals, in which neighboring Mn2+ ions and H atoms could form a Mn2+-O2--Mn2+ complex and Mn-H-Mn bridge structure. The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn3+-O2--Mn3+ complex, while the annealed samples exhibit their ferromagnetism, which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn2+-O2--Mn2+ complex

A ferroelectric photocatalyst Ag10Si4O13 with visible-light photooxidation properties

Ferroelectric p-block semiconductors are regarded as a new family of visible-light photocatalysts because of their dispersive and anisotropic band structures, as well as their intrinsic internal electric field. Silver silicates belong to this family and have band structures and an internal electric field that can be engineered by modulating the stoichiometry of Ag and SiO4. Here, we have developed a new ferroelectric p-block photocatalyst, Ag10Si4O13, by materials design and band engineering, which exhibits excellent photocatalytic activity towards the degradation of organic compounds, which is driven by visible light. Owing to the unique d10 and sp/p configurations in its electronic structure, Ag10Si4O13 possesses an indirect band gap of 1.72 eV with a highly dispersive conductive band and a flat valence band. This electronic structure promotes the generation, separation, and mobility of photo-induced charge carriers under visible-light illumination, which has been verified experimentally and theoretically. The compatible energy level of the conduction band determines its strong photo-oxidative capability. Moreover, the charge transfer process takes advantage of the existence of an internal electric field in Ag10Si4O13, which is attributed to the distorted SiO4 chain structure

Manipulation of domain wall mobility by oxygen vacancy ordering in multiferroic YMnO3

The mobility of the ferroelectric domain phases and the local conductivity of ferroelectric domain walls in multiferroic YMnO3 crystals grown in air and reduced atmosphere were studied by piezoresponse force microscopy (PFM), tip-enhanced Raman spectroscopy (TERS) and conductive atomic force microscopy (CAFM). Oxygen vacancies were found to reduce the strength of 4d–2p (Y3+–O2−) hybridization and structural trimerization distortion, leading to the disappearance of the six wedge-shaped ferroelectric domain phases in oxygen deficient YMnO3−δ crystals. We observed anisotropic domain wall motion such that the wedge-shaped domain configuration joined at one point could be changed to the stripe domain configuration by applying high electric fields in oxygen deficient YMnO3−δ single crystals. The local conductivity of the domain walls increased significantly in poled YMnO3−δ single crystals. The straight conductive domain walls in YMnO3−δ, instead of the twisted insulating ones in the stoichiometric crystal, are induced by the ordered oxygen vacancies which are verified by TERS measurements

Improving the solubility of Mn and suppressing the oxygen vacancy density in Zn0.98Mn0.02O nanocrystals via octylamine treatment

Zn0.98Mn0.02O nanocrystals were synthesized by the wet chemical route and were treated with different content of octylamine. The environment around Mn and the defect type and concentration were characterized by photoluminescence, Raman, X-ray photoelectron spectroscopy, and X-ray absorption fine structure. It is found that N codoping effectively enhances the solubility of Mn substituting Zn via reducing donor binding energy of impurity by the orbital hybridization between the N-acceptor and Mn-donor. On the other hand, the O atoms released from MnO6 and the N ions from octylamine occupy the site of oxygen vacancies and result in reduction of the concentration of oxygen vacancies in Zn0.98Mn0.02O nanocrystals

Bismuth oxybromide with reasonable photocatalytic reduction activity under visible light

The original bismuth-based oxyhalide, known as the Sillén family, is an important photocatalyst due to its high photocatalytic oxidation activity. Here, we report a bismuth-based photocatalyst, Bi24O 31Br10, with reasonable reduction activity. The photoreduction capability of Bi24O31Br10 in H2 evolution from water reduction is 133.9 μmol after 40 h under visible light irradiation. Bi24O31Br10 presents the highest activity among Bi2O3, BiOBr, and Bi 24O31Br10 in photocatalytic reduction of the Cr (VI) test, and Cr (VI) ions are totally removed in 40 min. The Mott-Schottky test shows the bottom of the conduction band fits the electric potential requirements for splitting water to H2. First-principles calculations indicate the conduction band of Bi24O31Br10 mainly consists of hybridized Bi 6p and Br 4s orbitals, which may contribute to the uplifting of the conduction band

Improving the Solubility of Mn and Suppressing the Oxygen Vacancy Density in Zn_0.98Mn_0.02O Nanocrystals via Octylamine Treatment

Zn_0.98Mn_0.02O nanocrystals were synthesized by the wet chemical route and were treated with different content of octylamine. The environment around Mn and the defect type and concentration were characterized by photoluminescence, Raman, X-ray photoelectron spectroscopy, and X-ray absorption fine structure. It is found that N codoping effectively enhances the solubility of Mn substituting Zn via reducing donor binding energy of impurity by the orbital hybridization between the N-acceptor and Mn-donor. On the other hand, the O atoms released from MnO₆ and the N ions from octylamine occupy the site of oxygen vacancies and result in reduction of the concentration of oxygen vacancies in Zn_0.98Mn_0.02O nanocrystals