Galvanic replacement mediated synthesis of hollow Pt nanocatalysts : significance of residual Ag for the H2 evolution reaction

With the increasing popularity of the galvanic replacement approach towards the development of bimetallic nanocatalysts, special emphasis has been focused on minimizing the use of expensive metal (e.g. Pt), in the finally formed nanomaterials (e.g. Ag/Pt system as a possible catalyst for fuel cells). However, the complete removal of the less active sacrificial template is generally not achieved during galvanic replacement, and its residual presence may significantly impact on the electrocatalytic properties of the final material. Here, we investigate the hydrogen evolution reaction (HER) activity of Ag nanocubes replaced with different amounts of Pt, and demonstrate how the bimetallic composition significantly affects the activity of the alloyed nanomaterial.

Galvanic replacement mediated transformation of Ag nanospheres into dendritic Au--Ag nanostructures in the ionic liquid [BMIM][BF4]

We demonstrate an unusual shape transformation of Ag nanospheres into {111}-oriented Au–Ag dendritic nanostructures by a galvanic replacement reaction in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]).

A study of localised galvanic replacement of copper and silver films with gold using scanning electrochemical microscopy

Galvanic replacement represents a highly significant process for the fabrication of bimetallic materials, but to date its application has been limited to either modification of large area metal surfaces or nanoparticles in solution. Here, the localised surface modification of copper and silver substrates with gold through the galvanic replacement process is reported. This was achieved by generation of a localised flux of AuCl4− ions from a gold ultramicroelectrode tip which interacts with the unbiased substrate of interest. The extent of modification with gold can be controlled through the tip–substrate distance and electrolysis time.

Galvanic Replacement of Semiconductor Phase I CuTCNQ Microrods with KAuBr4 to Fabricate CuTCNQ/Au Nanocomposites with Photocatalytic Properties

In this study, the reaction of semiconductor microrods of phase I copper 7,7,8,8-tetracyanoquinodimethane (CuTCNQ) with KAuBr4 in acetonitrile is reported. It was found that the reaction is redox in nature and proceeds via a galvanic replacement mechanism in which the surface of CuTCNQ is replaced with metallic gold nanoparticles. Given the slight solubility of CuTCNQ in acetonitrile, two competing reactions, namely CuTCNQ dissolution and the redox reaction with KAuBr4, were found to operate in parallel. An increase in the surface coverage of CuTCNQ microrods with gold nanoparticles occurred with an increased KAuBr4 concentration in acetonitrile, which also inhibited CuTCNQ dissolution. The reaction progress with time was monitored using UV−visible, FT-IR, and Raman spectroscopy as well as XRD and EDX analysis, and SEM imaging. The CuTCNQ/Au nanocomposites were investigated for their photocatalytic properties, wherein the destruction of Congo red, an organic dye, by simulated solar light was found dependent on the surface coverage of gold nanoparticles on the CuTCNQ microrods. This method of decorating CuTCNQ may open the possibility of modifying this and other metal-TCNQ charge transfer complexes with a host of other metals which may have significant applications.

Synthesis of CuTCNQ/Au microrods by galvanic replacement of semiconducting phase I CuTCNQ with KAuBr4 in aqueous medium

The spontaneous reaction between microrods of an organic semiconductor molecule, copper 7,7,8,8-tetracyanoquinodimethane (CuTCNQ) with [AuBr4]− ions in an aqueous environment is reported. The reaction is found to be redox in nature which proceeds via a complex galvanic replacement mechanism, wherein the surface of the CuTCNQ microrods is replaced with metallic gold nanoparticles. Unlike previous reactions reported in acetonitrile, the galvanic replacement reaction in aqueous solution proceeds via an entirely different reaction mechanism, wherein a cyclical reaction mechanism involving continuous regeneration of CuTCNQ consumed during the galvanic replacement reaction occurs in parallel with the galvanic replacement reaction. This results in the driving force of the galvanic replacement reaction in aqueous medium being largely dependent on the availability of [AuBr4]− ions during the reaction. Therefore, this study highlights the importance of the choice of an appropriate solvent during galvanic replacement reactions, which can significantly impact upon the reaction mechanism. The reaction progress with respect to different gold salt concentration was monitored using Fourier transform infrared (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS), as well as XRD and EDX analysis, and SEM imaging. The CuTCNQ/Au nanocomposites were also investigated for their potential photocatalytic properties, wherein the destruction of the organic dye, Congo red, in a simulated solar light environment was found to be largely dependent on the degree of gold nanoparticle surface coverage. The approach reported here opens up new possibilities of decorating metal–organic charge transfer complexes with a host of metals, leading to potentially novel applications in catalysis and sensing.

A study of the galvanic replacement reaction at surfaces and the role of lateral charge propagation

The galvanic replacement of isolated nanostructures of copper and silver on conducting supports as well as continuous films of copper with gold is reported. The surface morphology was characterized by scanning electron microscopy and the replacement with gold was confirmed by EDX analysis. It was found that lateral charge propagation during the replacement reaction had a significant effect in all cases. For the isolated nanostructures the deposition of gold was observed not only at the sacrificial template but also at the surrounding unmodified areas of the conducting substrate. In the case of copper films the role of lateral charge propagation was also confirmed by connecting it to an ITO electrode through an external circuit upon which gold deposition was also observed to occur. Interestingly, by inhibiting the rate of charge propagation, through the introduction of a series resistor, the morphology of gold on the copper substrate could be changed from discrete surface decoration with cube like nanoparticles to a more porous rough surface.

Lateral charge propagation effects during the galvanic replacement of electrodeposited MTCNQ (M= Cu, Ag) microstructures with gold and its influence on catalysed electron transfer reactions

The galvanic replacement of isolated electrodeposited semiconducting CuTCNQ microstructures on a glassy carbon (GC) substrate with gold is investigated. It is found that anisotropic metal nanoparticles are formed which are not solely confined to the redox active sites on the semiconducting materials but are also observed on the GC substrate which occurs via a lateral charge propagation mechanism. We also demonstrate that this galvanic replacement approach can be used for the formation of isolated AgTCNQ/Au microwire composites which occurs via an analogous mechanism. The resultant MTCNQ/Au (M = Cu, Ag) composite materials are characterized by Raman, spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and investigated for their catalytic properties for the reduction of ferricyanide ions with thiosulphate ions in aqueous solution. Significantly it is demonstrated that gold loading, nanoparticle shape and in particular the MTCNQ–Au interface are important factors that influence the reaction rate. It is shown that there is a synergistic effect at the CuTCNQ/Au composite when compared to AgTCNQ/Au at similar gold loadings.

Review of current test methods for screwed connections

The pull-through/local dimpling failure strength of screwed connections is very important in the design of profiled steel cladding systems to help them resist storms and hurricanes. The current American and European provisions recommend four different test methods for the screwed connections in tension, but the accuracy of these methods in determining the connection strength is not known. It is unlikely that the four test methods are equivalent in all cases and thus it is necessary to reduce the number of methods recommended. This paper presents a review of these test methods based on some laboratory tests on crest- and valley-fixed claddings and then recommends alternative tests methods that reproduce the real behavior of the connections, including the bending and membrane deformations of the cladding around the screw fasteners and the tension load in the fastener.

The effect of varied test instructions on neuropsychological performance following mild traumatic brain injury : an investigation of ‘diagnosis threat’

Diagnosis threat is a psychosocial factor that has been proposed to contribute to poor outcomes following mild traumatic brain injury (mTBI). This threat is thought to impair the cognitive test performance of individuals with mTBI because of negative injury stereotypes. University students (N= 45, 62.2% female) with a history of mTBI were randomly allocated to a diagnosis threat (DT, n=15), reduced threat (DT-reduced, n=15) or neutral (n=15) group. The reduced threat condition invoked a positive stereotype (i.e., that people with mTBI can perform well on cognitive tests). All participants were given neutral instructions before they completed baseline tests of: a) objective cognitive function across a number of domains; b) psychological symptoms; and, c) PCS symptoms, including self-reported cognitive and emotional difficulties. Participants then received either neutral, DT or DT-reduced instructions, before repeating the tests. Results were analyzed using separate mixed model ANOVAs; one for each dependent measure. The only significant result was for the 2 X 3 ANOVA on an objective test of attention/working memory, Digit Span, p<.05, such that the DT-reduced group performed better than the other groups, which were not different from each other. Although not consistent with predictions or earlier DT studies, the absence of group differences on most tests fits with several recent DT findings. The results of this study suggest that it is timely to reconsider the role of DT as a unique contributor to poor mTBI outcome.

Plant and animal microRNAs : similarities and differences

Plant and animal microRNAs (miRNAs) are evolutionarily ancient small RNAs, ∼19-24 nucleotides in length, that are generated by cleavage from larger highly structured precursor molecules. In both plants and animals, miRNAs posttranscriptionally regulate gene expression through interactions with their target mRNAs, and these targets are often genes involved with regulating key developmental events. Despite these similarities, plant and animal miRNAs exert their control in fundamentally different ways. Generally, animal miRNAs repress gene expression by mediating translational attenuation through (multiple) miRNA-binding sites located within the 3′ untranslated region of the target gene. In contrast, almost all plant miRNAs regulate their targets by directing mRNA cleavage at single sites in the coding regions. These and other differences suggest that the two systems may have originated independently, possibly as a prerequisite to the development of complex body plans. © Springer-Verlag 2005.

Perceptions of organ donors and willingness to donate organs upon death : a test of the prototype/willingness model

Understanding people's organ donation decisions may narrow the gap between organ supply and demand. In two studies, participants who had not recorded their posthumous organ donation decision (Study 1, N = 210; Study 2, N = 307) completed items assessing prototype/willingness model (PWM; attitude, subjective norm, donor prototype favorability and similarity, willingness) constructs. Attitude, subjective norm, and prototype similarity predicted willingness to donate. Prototype favorability and a Prototype Favorability × Similarity interaction predicted willingness (Study 2). These findings provide support for the PWM in altruistic health contexts, highlighting the importance of people's perceptions about organ donors in their donation decisions.

Multi-criteria optimization of group replacement schedules for distributed water pipeline assets

This thesis presents a multi-criteria optimisation study of group replacement schedules for water pipelines, which is a capital-intensive and service critical decision. A new mathematical model was developed, which minimises total replacement costs while maintaining a satisfactory level of services. The research outcomes are expected to enrich the body of knowledge of multi-criteria decision optimisation, where group scheduling is required. The model has the potential to optimise replacement planning for other types of linear asset networks resulting in bottom-line benefits for end users and communities. The results of a real case study show that the new model can effectively reduced the total costs and service interruptions.

Internet-enabled tourism entrepreneurs. International entrepreneurial values elicited through repertory test and laddering analysis

Although the tourism industry has been dramatically altered due to the Internet, there has been limited research published about international entrepreneurial values and Internet use in tourism firms. The findings of this study point to a relationship between the values of Internet-enabled international entrepreneurs in small-sized to medium-sized enterprises and the inclination of the firm to develop and initiate international activity. The findings of this study suggest that Internet-enabled tourism entrepreneurs share similar construct values. Two effective but underutilized qualitative methods were used in this study. The first method, repertory test, is an efficient technique for exploring constructs in decision making; the second method, laddering analysis, facilitates understanding of the perceived consequences and personal values guiding behaviour.