Magnetic properties of single crystalline Zn1−xCoxO thin films

We report on the magnetic properties of single crystalline thin films of Zn_1−xCo_xO (x=0.003–0.14) grown by plasma-assisted molecular beam epitaxy. In order to understand the role of intermediate charge carriers in the magnetic properties of this material two types of films were fabricated, with and without Ga-codoping. Magnetic measurements were made between 2 and 300 K in fields up to 5 T with a Quantum Design SQUID magnetometer. We found that all the tested films exhibit paramagnetic behavior following the Curie–Weiss law, χ=C/(T−θ), with negative Curie–Weiss temperatures and that this behavior holds even under strong n-doping. We show that the magnetization data, M(H), in function of the Co content provide additional evidence in favor of the antiferromagnetic Co–Co interaction in this material. We also observe that these data exhibit an ‘easy plane’ magnetic anisotropy for all the studied Co concentrations. Finally, we develop a simple cluster model, in order to describe the magnetic properties of ZnCoO, which is found to be in good agreement with our experiments.     

A cobalt (II) complex based on antipyrine derived schiff base as colorimetric sensor for Fe3+ ion

A novel complex [Co(NO₃)₂(APTY)₂H₂O] (1) is synthesized based on 1,5-dimethyl-2-phenyl-4-{[(1E)-pyridine-4-ylmethylene]amino}-1,2-dihydro-3H-pyrazol-3-one) antipyrine (APTY) and the structure of complex (1) is characterized via PXRD, SEM, FTIR and X-ray single crystal diffraction technique. It is found that the complex (1) has a good response to Fe³⁺ ion with colorimetric yellow change. In addition, we demonstrate that the sensing mechanism of complex (1) could is due to the disruption of complex (1) framework and the formation of complex Fe-APTY. The stability, rapid response and low detection limit enable this complex (1) to be a good Fe³⁺ ion chemical sensor for biological and environmental sensing applications.     

The influence of P/As substitution in the melilite‐like Na2Co(P2–xAsx)O7 (x = 0.40 and 0.93) solid solutions

To investigate the influence of P/As substitution on structures and electrical properties, e.g. the effect on material densities, two new solid P/As‐doped solutions, Na₂CoP_1.60As_0.40O₇ (disodium cobalt diphosphorus arsenic heptaoxide) and Na₂CoP_1.07As_0.93O₇ (disodium cobalt phosphorus arsenic heptaoxide), with melilite‐like structures have been synthesized by solid‐state reactions. Their unit‐cell parameters are in agreement with Vegard's law. The obtained structural models were investigated by the bond valence sum (BVS) and charge distribution (CHARDI) validation tools and, for the latter, the structures are described as being built on anion‐centred polyhedra. The frameworks can be described as layered and formed by {[Co(P,As)₂O₇]²⁻}_∞ slabs, with alkali cations sandwiched between the layers and with the interlayer spaces increased due to P/As substitution. The BVS model was extended to a preliminary simulation of the sodium conduction properties in the studied structural type and suggests that the most probable sodium conduction pathways are bidimensional, at the (002) planes.     

基于柔性四羧酸的三个一维/二维/三维Zn(Ⅱ)/Co(Ⅱ)配合物的晶体结构及荧光性质

通过水热/溶剂热合成的方法制备了3个Zn(Ⅱ)/Co(Ⅱ)配合物{[Zn(H₂L)(H₂O)₃]·H₂O·0.5H₄L}_n(1)、{[Co(L)_0.5(4,4'-bpy)]·0.5H₂O}_n(2)和{[Co(L)_0.5(pbmb)(H₂O)]·H₂O}_n(3)(H₄L=5,5'-(hexane-1,6-diyl)-bis(oxy)diisophthalic acid,4,4'-bpy=4,4'-bipyridine,pbmb=1,1'-(1,3-propane)bis-(2-methylbenzimidazole))。结构分析表明配合物1为一维链结构。2为拓扑符号为(6⁴·7·8)(6·7²)的三重穿插网络结构。3是拓扑符号为(4·6²)(4²·6²·8²)的(3,4)-连接的二维网络结构。配合物1呈现出较好的荧光性质。     

弱磁性Co0.85Se纳米片负载碳纳米管作为电催化析氢催化剂

氢气是一种环境友好可再生的清洁能源,电解水无疑是一种很好的制氢方法.然而,电催化分解水析氢受到其缓慢的动力学过程、较低的催化性能和较差的稳定性的限制.为了使整个过程更节能,具有高电流密度和低的过电势的高效电催化剂被广泛研究.非化学计量相硒化钴(Co0.85Se)作为一种重要的金属硫属化合物具有优异的催化性能而广受关注.但是低维的Co0.85Se活性位点少,分散性差,电子传递能力低,导致其电催化剂活性差.多壁碳纳米管(MWCNTs)具有多种电性能,包括金属导电性和电子存储能力等.因此,MWCNTs的特殊结构和高导电性可以有效地促进电子从电催化剂向碳纳米管的转移,实现高效电分解水制氢性能.本文在不使用表面活性剂和模板的情况下,通过一步水热溶剂热法合成弱磁性Co0.85Se纳米片负载碳纳米管电催化剂.采用磁滞回线研究Co0.85Se和MWCNTs/Co0.85Se的磁性能,结果表明其有弱顺磁性,Co0.85Se纳米片之间的空间距离增强导致粒子间偶极相互作用减弱,从而使MWCNTs/Co0.85Se纳米复合材料的矫顽力值增加到158 Oe.随着微晶尺寸的减小和纳米颗粒间距的增大,MWCNTs/Co0.85Se催化剂的比表面积增大,有利于提高其电催化活性.扫描电镜和透射电镜展示出Co0.85Se纳米片分散性较差,且团聚现象严重,而MWCNTs/Co0.85Se纳米复合催化剂显示Co0.85Se纳米片均匀分散在MWCNTs表面,且纳米片尺寸明显减小,有利于Co0.85Se纳米片暴露更多的活性位点.线性扫描伏安曲线测量表明,在酸性溶液中Co0.85Se纳米片在电流密度为10 mA cm?2时,其过电势为319 mV(vs.RHE),30 wt%MWCNTs/Co0.85Se的过电势为266 mV(vs.RHE).Co0.85Se和MWCNTs/Co0.85Se的Tafel斜率分别为92.6和60.5 mV dec?1.此外,MWCNTs/Co0.85Se的电流交换密度(j0)为0.07 mA cm?2.较小的Tafel斜率和高的电流交换密度表明,MWCNTs/Co0.85Se具有良好的反应动力学和快速的质子分离速率.交流阻抗谱表明MWCNTs/Co0.85Se比Co0.85Se电阻更小,电子传输速率更快.电化学活性表面积与双电层在固液界面处的电容测量值成正比.结果显示,30 wt%MWCNTs/Co0.85Se的双电层电容为0.22 mF cm^-2,高于Co0.85Se和15 wt%的rGO/Co0.85Se(0.04 mF cm^-2,0.17 mF cm^-2),这表明较大的电化学活性表面积有利于析氢反应进行.30 wt%MWCNTs/Co0.85Se的循环稳定测试表明其具有较好的稳定性.综上,本文介绍了通过一步水热法合成具有弱磁性的Co0.85Se和MWCNTs/Co0.85Se电催化剂,碳纳米管作为一种高导电性材料被引入Co0.85Se纳米片中以减少Co0.85Se的团聚,使Co0.85Se的活性位点增加,进而提高电催化制氢性能.     

Recent developments in Pt–Co catalysts for proton-exchange membrane fuel cells

Development of Pt-based oxygen reduction reaction catalysts with high efficiency and high durability is central to the application of proton-exchange membrane fuel cell systems. Pt–Co bimetallic catalysts have drawn extensive attention owing to their capability of delivering high performance and long lifetime for fuel cell applications including light-duty and heavy-duty vehicles. However, further improvements in durability and performance are needed to meet market requirements. To fully exploit the potential of Pt–Co catalysts, new insights into the relationship between catalyst properties and fuel cell performance and durability are needed, and more effective methods to tailor the features of Pt–Co catalysts need to be developed. This review provides a summary and perspective on recent efforts, including work on customizing the Pt shell and Pt:Co ratio, tailoring the crystal structure, and improving carbon support properties, with a particular emphasis on mechanisms leading to enhancement of mass activity, power density, and durability in membrane electrode assembly testing.     

Structural,Optical and Electrical Properties of Cu0.6CoxZn0.4−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) Soft Ferrites

A series of cobalt-inserted copper zinc ferrites, Cu_0.6Co_xZn_0.4−xFe₂O₄ (x = 0.0, 0.1, 0.2, 0.3, 0.4) having cubic spinel structure were prepared by the coprecipitation method. Various characterization techniques, including XRD, FTIR, UV-vis and I–V were used to investigate structural optical and electrical properties, respectively. The lattice constant was observed to be decreased as smaller ionic radii Co²⁺ (0.74 Å) replaced the higher ionic radii Zn²⁺ (0.82 Å). The presence of tetrahedral and octahedral bands was confirmed by FTIR spectra. Optical bandgap energy was determined in the range of 4.44–2.05 eV for x = 0.0 to 0.4 nanoferrites, respectively. DC electrical resistivity was measured and showed an increasing trend (5.42 × 10⁸ to 6.48 × 10⁸ Ω·cm) with the addition of cobalt contents as cobalt is more conductive than zinc. The range of DC electrical resistivity (10⁸ ohm-cm) makes these nanomaterials potential candidates for telecommunication devices.     

Rh/Co双金属纳米颗粒的制备及其催化制氢性能

以ISOBAM-104为保护剂,采用共还原法制备了一系列不同组成的Rh/Co双金属纳米颗粒(BNPs)。采用紫外-可见吸收光谱、透射电镜及高分辨透射电镜对纳米颗粒的结构及组成进行了表征。结果表明,所制备的Rh/Co BNPs的粒径小于6.0nm,具有合金结构。催化制氢实验结果表明,Rh_(20)Co_(80)BNPs具有最高的催化制氢活性,其TOF值可高达12880mol-H_2·h~(-1)·mol-Rh~(-1),远高于Rh和Co单金属纳米颗粒的催化活性。