A general strategy for bimetallic Pt-based nano-branched structures as highly active and stable oxygen reduction and methanol oxidation bifunctional catalysts

The morphology and size of Pt-based bimetallic alloys are known to determine their electrocatalytic performance in reactions relevant to fuel cells. Here, we report a general approach for preparing Pt-M (M = Fe, Co and Ni) bimetallic nano-branched structure (NBs) by a simple high temperature solution-phase synthesis. As-prepared Pt-M NBs show a polycrystalline structure and are rich in steps and kinks on the surface, which promote them favorable bifunctional catalytic properties in acidic electrolytes, specifically in terms of the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). Specially, Pt-Co NBs/C catalyst shows 6.1 and 5.3 times higher in specific activity (SA) and mass activity (MA) for ORR than state-of-the-art commercial Pt/C catalysts, respectively. Moreover, it exhibits a loss of 4.0% in SA and 14.4% in MA after 10,000 cycles of accelerated durability tests (ADTs) compared with the initial activities. In addition, we also confirmed the superior MOR activity of Pt-Co NBs/C catalyst in acidic electrolytes. For Pt-M NBs with other alloying metals, the ORR and MOR activities are both higher than commercial catalysts and are in the sequence of Pt-Co/C > Pt-Fe/C > Pt-Ni/C > commercial Pt/C (or PtRu/C). The improved activities and durability can benefit from the morphological and compositional effects. This synthesis approach may be applied to develop bifunctional catalysts with enhanced ORR and MOR properties for future fuel cells designs.

     

A new approach to well-defined, stable and site-isolated catalysts

A new concept to circumvent some of the problems that are hindering a rational metallic catalyst development is introduced. Investigation of conventional metal catalysts — which consist of supported metals, metal mixtures or alloys — is handicapped by the presence of a variety of active sites, their possible agglomeration, metal-support interactions as well as segregation of the components. In order to avoid most of the drawbacks, we employ well-defined, ordered and in-situ stable unsupported intermetallic compounds. Knowledge of the chemical bonding in the compounds and the defined neighbourhood of the active sites allows a rational approach to catalysts with excellent selectivity as well as long-term stability. The concept is demonstrated for the intermetallic compound PdGa, which is applied as catalyst for the selective hydrogenation of acetylene to ethylene.     

Organic molecular magnets-the search for stable building blocks

The greatest problem in creating organic molecular magnets seems to be to find systems in which there is a strong exchange interaction but which are also chemically and thermally stable. This paper discusses one possible solution to this problem, the use of ‘strain protection’, and the synthesis of stable strain-protected pi biradical, trioxytriangulene. This is the first representative of a new, unexplored family of pi biradicals, the non-Kekulé polynuclear aromatics.     

Organic molecular magnets-the search for stable building blocks

The greatest problem in creating organic molecular magnets seems to be to find systems in which there is a strong exchange interaction but which are also chemically and thermally stable. This paper discusses one possible solution to this problem, the use of strain protection, and the synthesis of stable strain-protected pi biradical, trioxytriangulene. This is the first representative of a new, unexplored family of pi biradicals, the non-Kekulé polynuclear aromatics.     

A stable,wideband tunable,near transform-limited,graphene-mode-locked,ultrafast laser

We report an ultrafast laser mode-locked with a graphene saturable absorber. The linear dispersions of the Dirac electrons in graphene enable wideband tunability. We get ∼1 ps pulses, tunable between 1525 and 1559 nm, with stable mode-locking, insensitive to environmental perturbations.     

设计稳定和可逆的锂-空气电池阴极催化剂的研究进展

锂-空气电池具有极高的理论能量密度,成为下一代最有希望的电化学能量储存技术之一。锂-空气电池的性能主要取决于空气阴极表面发生的电化学反应,因此,合理设计具有高稳定性和可逆性的阴极是实现商业化可行的锂-空气电池的关键所在。然而,传统碳基电极的不稳定性导致的副反应会限制电池容量及其循环性能,因此,需要寻找能够替代碳基电极的新型电极。本文首先结合锂-空气电池的结构和阴极反应原理,提出了目前锂-空气电池面临的挑战,然后基于碳基阴极的不稳定性分析总结了设计稳定和可逆的锂-空气电池阴极的方法,最后提出了阴极催化剂的合理设计和催化机理的深入理解对锂-空气电池阴极的性能改善起着决定性作用的观点。     

Preparation of stable Pd nanoparticles with tunable size for multiple immunolabeling in biomedicine

Stable Pd nanoparticles (PdNP) with a tunable size (3-15 nm) were synthesized by controlled chemical reduction of PdCl₂ with sodium citrate in water. The morphology of PdNP was characterized by transmission electron microscopy, while their stability in solution was verified by quasi-elastic light scattering and small-angle X-ray scattering. Intensive stirring of reacting mixture played a vital role in achieving reproducible particle sizes. Controlled changes of pH and initial concentrations were employed in fine-tuning particle size distributions. Finally, 10 nm PdNP were conjugated with goat anti-mouse IgG antibody as proved by electrophoresis (SDS-PAGE) and used for ultrastructural immunolabeling, which confirmed suitability of PdNP for multiple immunolabeling in biomedicine.     

Synthesis of CaOSiO2 compounds and their testing as heterogeneous catalysts for transesterification of sunflower oil

The powder mixtures of calcium oxide (CaO) and silica gel (SiO₂) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO_3, Ca₃Si₂O₇, Ca₂SiO₄ compounds and CaO/Ca₂SiO₄ two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV–vis diffuse reflectance spectroscopy (DRS), N₂ adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO·SiO₂ and 3CaO·SiO₂ calcined at 700?°C, and 3CaO·SiO₂ calcined at 900?°C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca₂SiO₄ complex mixture. The effect of different amount of catalyst used for transesterification (0.2–2?wt%) was analyzed using the most active catalyst i.e. 3CaO·SiO₂ calcined at 700?°C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO₃, Ca₃Si₂O₇ and Ca₂SiO₄, phases did not possess catalytic activity.     

A combination of tapered fibre and polarization controller in generating highly stable and tunable dual-wavelength C-band laser

This paper demonstrates the use of a tapered fibre in generating a highly stable and tunable dual-wavelength fibre laser. By unique arrangement of polarization controller, adjustable spacing range between 0.94 and 3.32 nm and side mode suppression ratio (SMSR) up to 50 dB were recorded. The results were achieved at laser pump power of 94.7 mW. The inter-modal interference is achieved through the use of a non-adiabatic tapered fibre, made by a systematic flame brushing technique. The tapered fibre suppresses the mode competition in the 3-m erbium-doped fibre (EDF) gain medium. Over 60 min, the laser exhibited very high stability with acceptable peak power and SMSR. The proposed EDF laser operates from 1556.71 to 1562.13 nm range.     

Symmetric growth of Pt ultrathin nanowires from dumbbell nuclei for use as oxygen reduction catalysts

This work demonstrates the synthesis of Pt ultrathin nanowires assisted by chromium hexacarbonyl [Cr(CO)₆]. The nanowires exhibit a uniform diameter of 2–3 nm. The length can reach up to several microns. It was found that Cr species produced dumbbell-like nuclei which play a pivotal role in the formation of the Pt nanowires. Such Pt nanowires can be tuned to nanocubes by simply decreasing the concentration of [Cr(CO)₆]. Compared to a commercial Pt/C catalyst (45 wt%, Vulcan, Tanaka) and Pt black (fuel cell grade, Sigma), the synthesized Pt nanowires exhibit superior performance in electrocatalytic oxygen reduction with a specific activity of 0.368 mA/cm², which was 2.7 and 1.8 times greater than that of Pt/C (0.138 mA/cm²) and Pt black (0.202 mA/cm²), respectively. The mass activity of Pt nanowires (0.088 mA/μg) is 2.3 times that of Pt black (0.038 mA/μg) and comparable to that of Pt/C (0.085 mA/μg).      

Attention and search conspicuity of motorcycles as a function of their visual context

BackgroundOver the years, PTWs’ number of accidents have increased dramatically and have accounted for a high percentage of the total traffic fatalities. The majority of those accidents occur in daylight, clear weather, and at light to moderate traffic conditions. The current study included two experiments. The first experiment evaluated the influence of PTW attention conspicuity on the ability of un-alerted viewers to detect it, whereas the second experiment evaluated the PTWs search conspicuity to alerted viewers. The independent variables in both experiments included driving scenarios (urban and inter-urban), PTW rider's outfit (black, white, and reflective) and PTW distance from the viewer.Method66 students participated in experiment 1. Every participant was presented with a series of pictures and was asked to report all the vehicle types present in each picture. Experiment 2 included 64 participants and incorporated the same pictures as experiment 1. However, in this experiment the participants were instructed to search the pictures for a PTW and to report its presence or absence as soon as they reach a decision.ResultsIn experiment 1 the detection of a PTW depended on the interaction between its distance from the viewer, the driving scenario and PTW rider's outfit. For an un-alerted viewer when the PTW was distant the different outfit conditions affected its’ attention conspicuity. In urban roads, where the background surrounding the PTW was more complex and multi-colored, the reflective and white outfits increased its attention conspicuity compared to the black outfit condition. In contrast, in inter-urban roads, where the background was solely a bright sky, the black outfit provided an advantage for the PTW detectability. In experiment 2, the average PTW detection rate of the alerted viewers was very high and the average reaction time to identify the presence of a PTW was the shortest in the inter-urban environment. Similar to the results of experiment 1, in urban environments the reflective and white clothing provided an advantage to the detection of the PTW, while in the inter-urban environment the black outfit presented an advantage. Comparing the results of the two experiments revealed that at the farthest distance, the increased awareness in the search conspicuity detection rates were three times higher than in the attention conspicuity.ConclusionsThe conspicuity of a PTW can be increased by using an appropriate rider's outfit that distinguishes him/her from the background scenery. Thus, PTW riders can actively increase their conspicuity by taking into account the driving route (crowded urban/inter urban), eventually increasing the probability of being detected by the other road users. In addition, increasing the alertness and expectancy of drivers to the presence of PTWs can increase their search conspicuity.     

A study of diffusion models and their application to porous catalysts

A new model of diffusion in porous catalysts is proposed, namely a macropore model. A comparison between test results and calculations indicates a close agreement.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 4, pp. 708–719, October, 1973.     

Polymer brushes as active nanolayers for tunable bacteria adhesion

Bacterial biofilm formation on implant surfaces is a frequent reason for the failure of many biomedical devices. Polymer brushes, thin nanolayers constituted of densely grafted macromolecules, are promising candidates to use in many biomedical applications to control attachment of bacteria to a surface. In this work five different polymer brushes were synthesized and tested with respect to their ability to regulate Staphylococcus aureus adhesion. Namely, two mixed brushes [consisting of poly(ethylene glycol) and a positively charged polymers, poly(2-vynil pyridine) or quartenized poly(2-vynil pyridine)] are investigated along with one-component brushes of the respective polymers. Bacterial adhesion was regulated over two orders of magnitude via altering the polymer brush composition.     

The use of mindmapping software for patent search and management

Modern information technologies and in particular the internet have revolutionized the patent information professionals' work in terms of speed of access and information comprehensiveness from both company internal and external digital sources. Here, I describe how the digital mindmapping technique can be used to complement existing intellectual property management software solutions to meet the challenge of optimizing and managing patent search workflows as well as to rapidly organise and access highly dynamic, heterogeneous and scattered patent information sources. Both eye catching and highly memorable and at the same time self-explanatory mindmapping examples are presented. These were designed to include basic and advanced level digital mindmapping features tailored to significantly speed up and maintain a high work quality level of patent search professionals. A special emphasis is put on the great benefit of organising and accessing the plethora of internet-based worldwide online patent registers through mindmapping, both in terms of managing the constantly changing deep links to the actual search options for e.g., legal status information, and keeping track of the offered level of content.     

一种以AOTF为核心的农药荧光检测系统

提出了一种将 AOTF 技术用于农药含量检测的荧光光谱系统。该系统分别采用以α-Quartz,TeO2 晶体作为声光介质的激发和发射色散元件 AOTF,以高压短弧氙灯为激发光源,利用光纤探测并传输荧光,由数据采集卡进行数据接收和 A/D 转换。该系统通过声光调制产生单色光,由超声射频的变化实现光谱扫描,没有机械调谐部件,故波长切换快、结构简单。西维因农药的荧光特性测量结果表明,系统的荧光波长范围为 500-750nm, 光谱分辨率为 10nm。当激发光波长为320nm,荧光波长为 647nm,西维因溶液浓度为 0.0-120.0μg/L 时,系统具有较好的线性关系,线性相关系数 r 为 0.9991。它可用于对粮食作物中的农药残留的检测和荧光光谱分析。     

Surface-modification of cellulose nanowhiskers and their use as nanoreinforcers into polylactide: A sustainably-integrated approach

In this study, bionanocomposites based on renewable cellulose nanowhiskers (CNWs) as nanofillers and renewable poly(l-lactide) (PLA) as polymeric matrix were successfully and straightforwardly prepared using melt-extrusion technique. Due to the affinity difference between hydrophobic PLA and hydrophilic CNWs, the surface of CNWs was directly modified in aqueous suspension (pH = 5.4 – citrate buffer) at ambient temperature in the presence of functional trialkoxysilanes bearing various organic moieties (alkyl, amino, and (meth)acryloxy). The surface-functionalization of CNWs was first investigated using methacryloxy-based trialkoxysilane as model. The influence of parameters such as the amount of silane agents and the post-treatment conditions were optimized on the surface-modification of methacryloxy-modified CNWs. FT-IR, TEM, WAXS and XPS analyses provided further evidences about the efficiency of the surface-modifications of CNWs. In a subsequent step, the chemically modified CNWs were successfully incorporated into PLA by melt-extrusion in the absence of solvent, without any alterations of their nanostructure after melt-processing. The thermal/mechanical properties of the resulting bionanocomposites were determined and shown to be enhanced when silanized CNWs were used as nanofillers.     

Zeolitic materials as catalysts for organic syntheses

The major applications of zeolitic materials are as cation exchangers, selective adsorbents, catalysts and catalyst supports (mainly in catalytic cracking, hydroisomerization and aromatics processing). Their use in the synthesis of hydrocarbon intermediates and fine chemicals is at an earlier stage of research, although several international reunions and reviews have already shown the improvement achieved by using these solids in conventional catalytic processes. This improvement is found mainly in activity, selectivity and environmental concerns, new more environmentally friendly routes having been found for processes which previously produced undesirable side reactions or high amounts of environmentally hazardous residues (with the subsequent economic considerations). More than a hundred references form the main body of the present piece of work, which has three major objectives, the first of which is to outline the main properties of zeolitic materials in relation to their use as catalysts in organic syntheses, the second to present an up to date bibliographic review of their use for such purposes and the third to show the main improvements that these materials present with respect to the more conventional catalysts.     

Molecular sieves as catalysts for aromatic bromination

Ring bromination of alkylbenzenes at room temperature was effectively performed on aromatic substrates catalyzed by zeolite 13X or mordenite after introduction of iron(III) ions. Other zeolites and ions were also studied. Almost quantitative yields of p- and o-bromo derivatives without dibromo or side-chain derivatives were obtained after 3–4 h when the reaction was performed in the dark. Bromination of benzene was not complete even at reflux temperature. The catalyst may be recycled many times for practical applications.