Real‐Time Imaging of Nanoscale Redox Reactions over Bimetallic Nanoparticles

The catalytic performance of bimetallic nanoparticles (NPs) strongly depends on their structural and compositional changes under reaction conditions. At the fundamental level, these changes are driven by redox reactions that occur on the surface of the NPs. The degree of complexity in the redox reactions is further amplified in bimetallic NPs because both metals can have their own reactions with the reactant molecules, in addition to any synergistic effects between the metal nanocatalysts and their reducible oxides. Here, the gas phase oxidation and reduction reactions, and the oxidation of carbon monoxide (CO) over Pt–Ni rhombic dodecahedron NPs with segregated Pt frames and Pt–Ni alloy NPs are investigated using in situ gas cell transmission electron microscopy. The real‐time observations show that NiO shell formation and Pt segregation are two important features during the oxidation and reduction of Pt–Ni NPs, respectively. Moreover, the two types of NPs evolved in different ways. By combining high‐resolution imaging, mass spectroscopy, and modeling, it is shown that the evolution of NP morphology and composition during redox reactions plays an important role in controlling the catalytic activity of the NPs.     

Metal–Organic Framework Derived Narrow Bandgap Cobalt Carbide Sensitized Titanium Dioxide Nanocage for Superior Photo‐Electrochemical Water Oxidation Performance

Despite recent progress in photo‐electrochemical (PEC) water oxidation systems for TiO₂‐based photoanodes, PEC performance improvement is still seriously hampered due to poor carrier transport efficiency and sluggish surface water oxidation kinetics of pristine TiO₂. Herein, for the first time a brand new metal–organic framework (MOF)‐derived Co₃C nanosheet with narrow bandgap energy is demonstrated, to effectively sensitize TiO₂ hollow cages as a heterostructure photoanode for PEC water oxidation. It is found that MOF‐derived Co₃C nanosheet with narrow bandgap characteristic can simultaneously accelerate the surface water oxidation kinetics and extend the light harvesting range of pristine TiO₂. Meanwhile, a uniquely matched type‐II heterojunction constructed between MOF‐derived Co₃C and TiO₂ results in an evidently spontaneous e^?/h⁺ separation. MOF‐derived Co₃C/TiO₂ heterostructure photoanodes bring about drastically improved PEC water oxidation performance. Specifically, MOF‐derived Co₃C‐3/TiO₂ photoanode with an optimized content of Co₃C achieves the highest photocurrent density and charge separation efficiency of 2.6 mA cm^?2 and 92.6% at 1.23 V versus reversible hydrogen electrode, corresponding to 201% and 152% improvement compared with pristine TiO₂ nanocages. The ingeniously prepared MOF‐derived Co₃C carbide with narrow bandgap energy as a cocatalyst paves new way to construct potentially high performance solar‐energy conversion system.     

Reprocessing of thermally oxidized aluminum arsenide (AlAs) in epitaxial multilayers without delamination

Annealing or processing of AlAs that has been subjected to a wet thermal oxidation process can result in severe delamination of material at the oxidation front. This paper reports a procedure for preventing this delamination and presents a possible cause for the delamination.     

808 nm半导体激光器烧结工艺的研究

研究了808 nm半导体激光器烧结过程中容易出现的"爬"铟现象,根据实验室的实验条件,采用了侧壁氧化结构来解决这个问题.制作了普通结构和侧壁氧化结构的激光器,烧结测试后发现:侧壁氧化结构的管芯烧结成品率可以达到95%以上,比普通结构的烧结成品率提高了20%.再将这两批管芯在500mA下老化测试,发现:侧壁氧化的管芯寿命明显长于普通结构的管芯.     

具有多种输出模式微弧氧化电源的研制

基于对微弧氧化工艺和负载特性的研究,提出一种新的带放电回路脉冲模式。并在此基础上研制了一种以80C196KB单片机为控制系统核心,具有多种输出模式的微弧氧化电源。通过对主电路结构的拓扑及对可控硅触发和IGBT驱动的控制,该电源能够产生带放电回路脉冲、单极性脉冲和双极性脉;中3种输出模式,而且其脉冲幅值、频率、占空比具有很宽的调节范围。此外还实现了对微弧氧化过程中电流和电压的实时采集和显示。经实践表明,该电源能很好地应用于实验研究及工业化生产。     

AFM电场诱导氧化加工作用的分析

纳米加工技术是纳米器件研究的重要基础条件，纳米氧化结构则是纳米器件的重要组成部分。为了深化对AFM电场诱导氧化加工机理的理解，本文对Si表面的电场诱导氧化作用进行了实验研究，包括探针与样品之间实际电压的监测、不同掺杂Si材料加工门槛电压的分析及探针扫描速率对氧化物高度的影响。实验分析表明，在氧化结构的生成过程中存在的充放电过程是不同加工门槛电压的产生和氧化作用时间与氧化线高度呈非线性关系的重要影响因素。     

Direct synthesis of Fe-ZSM-5 zeolite and its prospects as efficient electrode material in methanol fuel cell

New method of direct synthesis of Fe-ZSM-5 zeolite using tetrapropyl ammonium bromide (TPABr) as the template is reported in this study. The synthesis was based on one step procedure and did not involve the usual ion-exchange step to effect incorporation of the metal ion. The zeolite sample was characterized by XRD, FT-IR, TGA, SEM with EDX, and BET adsorption techniques. The average diameter of the porous particle of zeolite was about 10 µm and it was a spherical cluster of crystals of about 141 nm long along one of its axis. Zeolite-modified glassy carbon electrode (GCE) was prepared by using the mixture of the synthesized zeolite and carbon black (Vulcan X-72) and casting it as a thin layer. With modified GCE as the working electrode, the oxidation of methanol in alkaline medium was studied by cyclic voltammetry. The response of the electrode for methanol oxidation in alkaline medium is promising and it highlights the candidature of the synthesized material for methanol fuel cell. The electrochemical behavior of Fe-ZSM-5 in acidic medium reveals the oxidation state of iron in the zeolite. Cationic iron in the zeolite framework imparts electrocatalytic activity for methanol oxidation.     

类胡萝卜素抑制食用油脂光敏氧化的研究

业甲基蓝作光敏剂,研究了类胡萝卜素在豆油、菜油中的抗油脂光敏氧化作用。结果表明,类胡萝卜素可有效抑制油脂的光敏氧化剂且抑制作用随浓度升高而增强,类胡萝卜素抑制油脂光敏氧化的与其结构中的共轭双键数有关。     

Comparison of the effects of black and green tea on in vitro lipoprotein oxidation in human serum

Lipoprotein oxidation is a process thought to be involved in atherogenesis. Dietary antioxidants that prevent or inhibit oxidative damage to lipoproteins may help to prevent atherosclerosis. Both black and green teas can be major dietary sources of flavonoids and other phenolics with antioxidant activity. Results of previous studies suggest that green tea may have a greater antioxidant potential than black tea. The aim of this study was to assess and compare the effects of black and green tea on in vitro lipoprotein oxidation. The tea extracts were prepared using a method similar to that used to prepare infusions of tea for drinking. Antioxidant activities of seven black teas and four green teas were assessed using an in vitro assay that measures Cu²⁺ ‐induced oxidation of lipoproteins in human serum. All tea extracts inhibited in vitro lipoprotein oxidation in human serum to a similar extent. No significant difference in antioxidant activity was found between black and green tea. Caffeine prepared to a comparable concentration to that found in tea had no effect on lipoprotein oxidation. Further studies are required to determine the importance of these findings in relation to possible protective effects of black and green tea consumption against atherogenesis and cardiovascular disease. © 1999 Society of Chemical Industry