Carbon dioxide adsorption studies on delafossite CuFeO2 hydrothermally synthesized

Delafossite CuFeO₂ oxide was synthesized by a hydrothermal technique using Cu₂O and FeOOH as precursors with the addition of fused NaOH as mineralizer. The amount of rhombohedral and hexagonal delafossite phase formed depends on the synthesis time lapses between 2 and 5 days and on the NaOH concentration. The compounds obtained were analyzed with Raman Spectroscopy, X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) in order to obtain their morphological and structural properties. Optical behavior was studied by UV–vis Spectroscopy and gas adsorption measured with a Quartz-Crystal Microbalance (QCM). Our results show that this type of hydrothermal synthesis is capable of recreating the delafossite-type structure of copper-iron oxide and produces a high yield of material with the right stoichiometry. The highest uptake of carbon dioxide is observed on the sample with the highest ratio between rhombohedral and hexagonal delafossite phase.     

Novel titanate nanotubes-cyanocobalamin materials: Synthesis and enhanced photocatalytic properties for pollutants removal

New hybrid nanomaterials, with improved photocatalytic performance in pollutants removal, were obtained through the modification of titanate nanotubes (TNT) with a cobalt porphyrin, the cyanocobalamin, also knowing as vitamin B12 (B12). The nanocrystalline TNT were produced by hydrothermal treatment and after treated with cobalamin to produce B12-TNT materials. The characterization of the new hybrid material was performed by XRD, FTIR, TEM-EDS, DRS, XPS and ICP. The results show that the immobilization of the cobalt containing specie is dependent on the point of zero charge of the TNT and no modifications on the structure and morphology were observed. No significant changes in the optical band gap were observed after B12 incorporation, but an increasing in the visible light absorption, which arises from charge transfer and d–d transitions of the cobalt, was visualized. The samples photocatalytic performance was studied for the hydroxyl radical production and the highest catalytic ability was achieved by the B12-HTNT sample. The catalytic ability of these new hybrid nanomaterials for two model pollutants photodegradation, phenol and rhodamine B (RhB) was investigated. For both pollutants, the best results were achieved using B12-HTNT with a removal of 94% of a 10 ppm RhB and 87% of a 20 ppm phenol solution in 90 min of irradiation (150 mL, 0.2 g catalyst/L).     

Multiscale Approach to the Study of the Electronic Properties of Two Thiophene Curcuminoid Molecules

We studied the electronic and conductance properties of two thiophene–curcuminoid molecules, 2‐thphCCM ( 1 ) and 3‐thphCCM ( 2 ), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO–LUMO band gap energies, showing that molecule 1 has lower values than 2 . Theoretical calculations show the same trend. Self‐assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO–LUMO gap in both molecules to almost the same value. Single‐molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes.     

The band alignment at CdS/Cu2ZnSnSe4 heterojunction interface

Band alignment at CdS/Cu₂ZnSnSe₄ heterojunction interface is studied by X‐ray photoemission spectroscopy. The Cu₂ZnSnSe₄ thin films are prepared by selenization of electrodeposited Cu‐Zn‐Sn precursors. CdS overlayers with different thickness are sequentially grown on the Cu₂ZnSnSe₄ substrate by pulsed laser deposition process. Photoemission spectra are obtained before and after each growth to study the conduction and valence band offsets at the heterojunction interface. The determined conduction band offset of 0.34 eV indicates a spike‐like ‘type I’ band alignment at CdS/Cu₂ZnSnSe₄ interface. The spike will avoid interface recombination, and it is low enough that electron could transfer from the Cu₂ZnSnSe₄ layer to the buffer layer which is suitable for solar cell's fabrication. Copyright © 2012 John Wiley & Sons, Ltd.     

自掺杂TiO2纳米管：液相制备及光催化性能

采用水合肼（N₂H₄·H₂O）作为还原剂,在液相环境中制备了自掺杂TiO₂纳米管阵列（NTs）。利用FE-SEM、EDS、XPS、XRD、Raman、UV-Vis/NIR分光光度法以及半导体特性分析系统（Keithley 4200 SCS）分别对样品的形貌,晶体结构,光学特性以及电学性能进行了表征。结果表明：通过这种方法制备的自掺杂TiO₂NTs在带隙中引入了大量的氧空位,创造了氧空位能级,从而提高了样品的电导率,有效提高光生电子-空穴对的产生、分离和传输。此外,由于氧空位的作用,使得TiO₂NTs的带隙变窄,增强了可见光吸收能力,致使样品具有较高的光催化活性,并通过降解甲基橙溶液对样品的光催化活性进行评估。结果显示当光照150min后,自掺杂TiO₂NTs对甲基橙溶液的降解率达73%,并且这种催化剂便于回收和重复使用。     

Surface effect on band structure of magneto-elastic phononic crystal nanoplates subject to magnetic and stress loadings

This paper presents a theoretical model for the size-dependent band structure of magneto-elastic phononic crystal(PC) nanoplates according to the Kirchhoff plate theory and Gurtin-Murdoch theory, in which the surface effect and magneto-elastic coupling are considered. By introducing the nonlinear coupling constitutive relation of magnetostrictive materials, Terfenol-D/epoxy PC nanoplates are carried out as an example to investigate the dependence of the band structure on the surface effect, magn...     

石墨烯能带中的重叠矩阵效应:Tight-Binding方法在模拟中的研究

采用紧束缚方法计算了石墨烯的价带(π)和导带(π*),考虑了非正交基矢下重叠矩阵效应,重叠积分参量s越小,导带越靠近费米面,而价带越远离费米面.在重叠积分参量s≤0.1时,基本保持了原子在实际空间中重叠所引起的能带的改变,太大(s=0.4)则会导致物理上失效.计算了石墨烯的能态密度,在费米面ε=0处(对应Dirac点)的能态密度为零,并且在Dirac点附近呈线性变化.     

高压下锐钛矿TiO2的电阻率及能带结构的研究

应用在位电阻率测量方法研究高压下锐钛矿TiO2的电学性质. 通过研究电阻率随压力变化的异常变化点, 观察到了TiO2从锐钛矿-柯铁矿-斜锆石的相变. 卸压后,电阻率和初始值相差2个数量级, 说明该相变为不可逆相变. 结合第一性原理计算结果表明, 柯铁矿结构更小的带隙是导致TiO2电阻率减小的根本原因.     

量子受限效应和对称性效应对硅光子晶体禁带的影响

光子晶体不仅可以用来调控自发辐射, 还可以用来控制光的传输和局域. 采用平面波展开法进行模拟计算, 分析硅背景下的二维正方、三角晶格光子晶体散射基元的形状和空间取向对光子禁带的影响. 计算结果表明: 对称性和量子受限效应之间的竞争是导致光子晶体禁带宽度发生变化的原因.     

基于频带分解和距离加权的单矢量水听器浅海被动测距方法研究

本文针对浅海环境下中低频宽带脉冲声源被动测距问题, 提出了一种声压和水平振速联合处理的被动测距方法. 在浅海波导中, 声压和质点振速的自相关函数卷绕(warping)谱具有稳定的频率特征. 声压和水平振速的自相关卷绕谱具有相同的准线谱特征, 垂直振速自相关卷绕谱具有宽谱叠加线谱的特征, 与声压自相关卷绕谱相比, 其尖峰个数比更多, 且尖峰宽度更宽. 利用引导源, 本文提出了基于频带分解和距离加权的声压和水平振速联合被动测距方法. 利用该方法对2008年冬季青岛海域综合实验中单矢量水听器接收的气枪信号进行处理, 结果表明, 该方法能够实现气枪声源的有效测距. 与传统单声压水听器被动测距方法相比, 该方法可以有效减小代价函数的主瓣宽度、提高测距精度.