Methanol tolerant oxygen-reduction activity of carbon supported platinum–bismuth bimetallic nanoparticles

The oxygen reduction activity and methanol tolerance of Pt–Bi/C electrocatalysts were studied using electrochemical voltammetric techniques including rotating ring-disk electrode. The Pt–Bi/C catalyst was prepared via a polyol method and subjected to heat treatment to increase the degree of alloying. X-ray diffraction studies revealed the unalloyed character of the as-prepared catalyst and alloy formation upon heat treatment. The electrochemical behaviour of both catalysts showed different behaviour in dilute acid electrolytes, namely sulphuric and perchloric acids. In both electrolytes, the oxygen reduction reaction was found to occur via the four-electron process revealing that the mechanism of oxygen reduction is unaltered even in the presence of excess of methanol. Pt–Bi/C catalyst material showed dramatically different properties and reactivity with respect to oxygen reduction activity and methanol tolerance in perchloric and sulphuric acids. The onset potential for oxygen reduction reaction (ORR) significantly shifted by about 100 mV to more negative values and at the same time the current density was significantly enhanced. This type of non-ideal methanol-tolerant behaviour among Pt bimetallics and a “trade off” is common with all the known so-called methanol tolerant combinations of Pt. In general, the Pt–Bi surface appeared to have a negligibly lesser sensitivity towards methanol activity compared to pure platinum.     

Minimizing decomposition of vaporized hydrogen peroxide for biological decontamination of galvanized steel ducting

The behavior of vaporous hydrogen peroxide (VHP) was examined in clean, room-scale galvanized steel (GS) and polyvinylchloride-coated steel air ducts, to understand how it might be used to decontaminate larger ventilation systems. VHP injected into the GS duct decreased in concentration along the length of the duct, whereas VHP concentrations in the polyvinylchloride coated duct remained essentially constant, suggesting that VHP decomposed at the GS surface. However, decomposition was reduced at lower temperatures (approximately 22 degrees C) and higher flow rates (approximately 80 actual cubic meter per hour). A computational fluid dynamics model incorporating reactive transport was used to estimate surface VHP concentrations where bioaerosol contamination is likelyto reside, and also showed that VHP decomposition was enhanced at bends within the duct, compared to straight sections. Use of G. stearothermophilus indicators, in conjunction with model estimates, indicated that a concentration-contact time of approximately 100 mg/L H2O2(g) x min was required to achieve a 6 log reduction of indicator spores in clean GS duct, at 30 degrees C. When VHP is selected for building decontamination, this work suggests the most efficacious strategy may be to decontaminate GS ducting separately from the rest of the building, as opposed to a single decontamination event in which the ventilation system is used to distribute VHP throughout the entire building.     

Mannopyranoside Glycolipids Inhibit Mycobacterial and Biofilm Growth and Potentiate Isoniazid Inhibition Activities in M. smegmatis

Lipomannan and lipoarabinomannan are integral components of the mycobacterial cell wall. Earlier studies demonstrated that synthetic arabinan and arabinomannan glycolipids acted as inhibitors of mycobacterial growth, in addition to exhibiting inhibitory activities of mycobacterial biofilm. Herein, it is demonstrated that synthetic mannan glycolipids are better inhibitors of mycobacterial growth, whereas lipoarabinomannan has a higher inhibition efficiency to biofilm. Syntheses of mannan glycolipids with a graded number of mannan moieties and an arabinomannan glycolipid are conducted by chemical methods and subsequent mycobacterial growth and biofilm inhibition studies are conducted on Mycobacterium smegmatis. Growth inhibition of (73±3) % is observed with a mannose trisaccharide containing a glycolipid, whereas this glycolipid did not promote biofilm inhibition activity better than that of arabinomannan glycolipid. The antibiotic supplementation activities of glycolipids on growth and biofilm inhibitions are evaluated. Increases in growth and biofilm inhibitions are observed if the antibiotic is supplemented with glycolipids, which leads to a significant reduction of inhibition concentrations of the antibiotic.     

Hierarchical NiMoS and NiFeS Nanosheets with Ultrahigh Energy Density for Flexible All Solid‐State Supercapacitors

Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free‐standing Ni?Mo?S and Ni?Fe?S nanosheets (NSs) for high‐performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni²⁺ is optimized to attain hierarchical Ni?Mo?S and Ni?Fe?S NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of Ni?Mo?S and Ni?Fe?S NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g^?1 at 1 mA cm^?2), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm^?2, respectively), and superior cycling stabilities. Most importantly, a flexible Ni?Mo?S NS//Ni?Fe?S NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm^?3, excellent energy density of ≈82.13 Wh kg^?1 at 0.561 kW kg^?1, exceptional power density (≈13.103 kW kg^?1 at 61.51 Wh kg^?1) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.     

Optimisation of hybridisation effect in graphene reinforced polymer nanocomposites

This article focuses on the optimisation of electrical and mechanical properties of hybrid blends of polyoxymethylene (POM) as primary thermoplastic matrix, polypyrrole (PPY) as secondary conducting polymer and graphene (G) as reinforcement. An initial Taguchi analysis was performed with a focus on improving electrical conductivity (σ) and tensile strength. A mixture analysis using ‘simplex’ statistical design was applied to develop an experimental subset that identified an optimal combination in weight-percentage. Both electrical and mechanical properties were improved by the addition of PPY and graphene particles due to hybridisation mechanism as well as double percolation threshold. The maximum electrical conductivity of 0.95 S cm^?1 was achieved with POM reinforced with 3 wt.% of G and 2.5 wt.% of PPY loading. The mechanical properties were found to be increased with increase in addition of both G and PPY.     

Interference Mitigation Based on Radio Aware Channel Assignment for Wireless Mesh Networks

An intricate network deployment for high demand users leads to simultaneous transmission in wireless mesh networks. Multiple radios are adapted to individual nodes for improving network performance and Quality of Service (QoS). However, whenever multiple radios are assigned to the same channel, co-located radio interference occurs, which poses a major drawback. This paper proposes a Radio aware Channel Assignment (Ra-CA) mechanism based on a direct graphical model for mitigation of interference in multi-radio multi-channel networks. Initially, the co-located radio interference is identified by classifying non-interfering links for simultaneous transmission in the network. Proposed channel assignment mechanism helps in allocating the minimal number of channels to the network that mitigate co-located radio interference. Performance analysis of the proposed Ra-CA strategy is carried out compared with other existing techniques, like Breadth First Search-Channel Assignment (BFS-CA) and Maximal Independent Set Channel Assignment (MaIS-CA), in multi-radio networks. Simulation results demonstrate that the proposed channel assignment scheme is more efficient compared to the existing ones, in terms of QoS parameters like, packet drop rate, packet delivery ratio, transmission delay and throughput.     

Cucurbiturils as Reaction Containers for Photocycloaddition of Olefins

The [2+2] photocycloaddition (PCA [2+2]) of alkenes is one of the most synthetically useful photoreactions. It is a convenient one-step reaction that is useful for generating substituted cyclobutanes, polymers, and biologically relevant molecules. However, the reaction efficiency is limited by its bimolecular nature requiring encounter between two reactants within the narrow window of excited state lifetime of the photoactive alkene, and competition from the unimolecular photoisomerization. Our groups have utilized macrocyclic cavitands, especially cucurbiturils(CB), to confine two alkene molecules within their cavities and steer them towards a single dimer regio- and stereoselectively. Although, primarily the review focuses on photocycloaddition within CBs, such reactions in closely related cavitands such as cyclodextrins (CD) and calixarenes (CA) are also briefly mentioned to provide a comparison with CBs. Studies on photocycloaddition of olefins within CB by other research groups are also briefly highlighted. A mechanistic model, with ability to predict the nature of the dimer product formed within the above reaction containers is included.     

Structural Basis for Metastability in Amorphous Calcium Barium Carbonate (ACBC)

Metastable amorphous precursors are emerging as valuable intermediates for the synthesis of materials with compositions and structures far from equilibrium. Recently, it was found that amorphous calcium barium carbonate (ACBC) can be converted into highly barium‐substituted “balcite,” a metastable high temperature modification of calcite with exceptional hardness. A systematic analysis ACBC (Ca_1‐xBa_xCO₃·1.2H₂O) in the range from x = 0–0.5 is presented. Combining techniques that independently probe the local environment from the perspective of calcium, barium, and carbonate ions, with total X‐ray scattering and a new molecular dynamics/density functional theory simulations approach, provides a holistic picture of ACBC structure as a function of composition. With increasing barium content, ACBC becomes more ordered at short and medium range, and increasingly similar to crystalline balcite, without developing long‐range order. This is not accompanied by a change in the water content and does not carry a significant energy penalty, but is associated with differences in cation coordination resulting from changing carbonate anion orientation. Therefore, the local order imprinted in ACBC may increasingly lower the kinetic barrier to subsequent transformations as it becomes more pronounced. This pathway offers clues to the design of metastable materials by tuning coordination numbers in the amorphous solid state.     

Differential scanning calorimetry and wide-angle X-ray scattering studies of bread staling

Wide angle X-ray scattering (WAXS) was used to follow the development of crystal size and strain during the staling of bread containing different additives. In this it was observed that one can classify the good anti-staling additives as gelatin, propylene glycol, maltodextrin and anti-staling enzyme corresponding to the order of increasing crystal size for a particular Bragg reflection in all the samples and correlate using DSC (differential scanning calorimetry) studies of all the bread compositions containing different additives. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1597–1603, 1998