Role of charge in destabilizing AlH4 and BH4 complex anions for hydrogen storage applications : Ab initio density functional calculations

NaAlH4 and LiBH4 are potential candidate materials for mobile hydrogen storage applications, yet they have the drawback of being highly stable and desorbing hydrogen only at elevated temperatures. In this letter, ab initio density functional theory calculations reveal how the stabilities of the AlH4 and BH4 complex anions will be affected by reducing net anionic charge. Tetrahedral AlH4 and BH4 complexes are found to be distorted with the decrease of negative charge. One H-H distance becomes smaller and the charge density will overlap between them at a small anion charge. The activation energies to release of H2 from AlH4 and BH4 complexes are thus greatly decreased. We demonstrate that point defects such as neutral Na vacancies or substitution of a Na atom with Ti on the NaAlH4(001) surface can potentially cause strong distortion of neighboring AlH4 complexes and even induce spontaneous dehydrogenation. Our results help to rationalize the conjecture that the suppression of charge transfer to AlH4 and BH4 anion as a consequence of surface defects should be very effective for improving the recycling performance of H2 in NaAlH4 and LiBH4. The understanding gained here will aid in the rational design and development of hydrogen storage materials based on these two systems.

Early childhood teachers' pedagogical practice : what they know, think and do with young children experiencing parental separation and divorce

This grounded theory study examined the practices of twenty-one Australian early childhood teachers who work with children experiencing parental separation and divorce. Findings showed that teachers constructed personalised support for these children. Teachers’ pedagogical decision-making processes had five phases: constructing their knowledge, applying their knowledge, applying decision-making schema, taking action, and monitoring action and evaluating. This study contributes new understandings about teachers’ work with young children experiencing parental separation and divorce, and extends existing theoretical frameworks related to the provision of support. It adds to scholarship by applying grounded theory methodology in a new context. Recommendations are made for school policies and procedures within and across schools and school systems.

Development and validation of a ultra performance LC-ESI/MS method for analysis of metabolic phenotypes of healthy men in day and night urine samples

Ultra-performance LC coupled to quadrupole TOF/MS (UPLC-QTOF/MS) in positive and negative ESI was developed and validated to analyze metabolite profiles for urine from healthy men during the day and at night. Data analysis using principal components analysis (PCA) revealed differences between metabolic phenotypes of urine in healthy men during the day and at night. Positive ions with mass-to-charge ratio (m/z) 310.24 (5.35 min), 286.24 (4.74 min) and 310.24 (5.63 min) were elevated in the urine from healthy men at night compared to that during the day. Negative ions elevated in day urine samples of healthy men included m/z 167.02 (0.66 min), 263.12 (2.55 min) and 191.03 (0.73 min), whilst ions m/z 212.01 (4.77 min) were at a lower concentration in urine of healthy men during the day compared to that at night. The ions m/z 212.01 (4.77 min), 191.03 (0.73 min) and 310.24 (5.35 min) preliminarily correspond to indoxyl sulfate, citric acid and N-acetylneuraminic acid, providing further support for an involvement of phenotypic difference in urine of healthy men in day and night samples, which may be associated with notably different activities of gut microbiota, velocity of tricarboxylic acid cycle and activity of sialic acid biosynthesis in healthy men as regulated by circadian rhythm of the mammalian bioclock.

A simple method for fabricating 3-D multilayered composite scaffolds

One limitation of electrospinning stems from the charge build-up that occurs during processing, preventing further fibre deposition and limiting the scaffold overall thickness and hence their end-use in tissue engineering applications targeting large tissue defect repair. To overcome this, we have developed a technique in which thermally induced phase separation (TIPS) and electrospinning are combined. Thick three-dimensional, multilayered composite scaffolds were produced by simply stacking individual polycaprolactone (PCL) microfibrous electrospun discs into a cylindrical holder that was filled with a 3% poly(lactic-co-glycolic acid) (PLGA) solution in dimethylsulfoxide (a good solvent for PLGA but a poor one for PCL). The construct was quenched in liquid nitrogen and the solvent removed by leaching out in cold water. This technique enables the fabrication of scaffolds composed principally of electrospun membranes that have no limit to their thickness. The mechanical properties of these scaffolds were assessed under both quasi-static and dynamic conditions. The multilayered composite scaffolds had similar compressive properties to 5% PCL scaffolds fabricated solely by the TIPS methodology. However, tensile tests demonstrated that the multilayered construct outperformed a scaffold made purely by TIPS, highlighting the contribution of the electrospun component of the composite scaffold to enhancing the overall mechanical property slate. Cell studies revealed cell infiltration principally from the scaffold edges under static seeding conditions. This fabrication methodology permits the rapid construction of thick, strong scaffolds from a range of biodegradable polymers often used in tissue engineering, and will be particularly useful when large dimension electrospun scaffolds are required.

Development of modified inorganic adsorbents for radioactive iodine removal and biomolecule adsorption

Development and application of inorganic adsorbent materials have been continuously investigated due to their variability and versatility. This Master thesis has expanded the knowledge in the field of adsorption targeting radioactive iodine waste and proteins using modified inorganic materials. Industrial treatment of radioactive waste and safety disposal of nuclear waste is a constant concern around the world with the development of radioactive materials applications. To address the current problems, laminar titanate with large surface area (143 m2 g−1) was synthesized from inorganic titanium compounds by hydrothermal reactions at 433 K. Ag2O nanocrystals of particle size ranging from 5–30 nm were anchored on the titanate lamina surface which has crystallographic similarity to that of Ag2O nanocrystals. Therefore, the deposited Ag2O nanocrystals and titanate substrate could join together at these surfaces between which there forms a coherent interface. Such coherence between the two phases reduces the overall energy by minimizing surface energy and maintains the Ag2O nanocrystals firmly on the outer surface of the titanate structure. The combined adsorbent was then applied as efficient adsorbent to remove radioactive iodine from water (one gram adsorbent can capture up to 3.4 mmol of I- anions) and the composite adsorbent can be recovered easily for safe disposal. The structure changes of the titanate lamina and the composite adsorbent were characterized via various techniques. The isotherm and kinetics of iodine adsorption, competitive adsorption and column adsorption using the adsorbent were studied to determine the iodine removal abilities of the adsorbent. It is shown that the adsorbent exhibited excellent trapping ability towards iodine in the fix-bed column despite the presence of competitive ions. Hence, Ag2O deposited titanate lamina could serve as an effective adsorbent for removing iodine from radioactive waste. Surface hydroxyl group of the inorganic materials is widely applied for modification purposes and modification of inorganic materials for biomolecule adsorption can also be achieved. Specifically, γ-Al2O3 nanofibre material is converted via calcinations from boehmite precursor which is synthesised by hydrothermal chemical reactions under directing of surfactant. These γ-Al2O3 nanofibres possess large surface area (243 m2 g-1), good stability under extreme chemical conditions, good mechanical strength and rich surface hydroxyl groups making it an ideal candidate in industrialized separation column. The fibrous morphology of the adsorbent also guarantees facile recovery from aqueous solution under both centrifuge and sedimentation approaches. By chemically bonding the dyes molecules, the charge property of γ-Al2O3 is changed in the aim of selectively capturing of lysozyme from chicken egg white solution. The highest Lysozyme adsorption amount was obtained at around 600 mg/g and its proportion is elevated from around 5% to 69% in chicken egg white solution. It was found from the adsorption test under different solution pH that electrostatic force played the key role in the good selectivity and high adsorption rate of surface modified γ-Al2O3 nanofibre adsorbents. Overall, surface modified fibrous γ-Al2O3 could be applied potentially as an efficient adsorbent for capturing of various biomolecules.

Modified alumina nanofiber membranes for protein separation

Large-scale purification/separation of bio-substances is a key technology required for rapid production of biological substances in bioengineering. Membrane filtration is a new separation process and has potential to be used for concentration (removal of solvent), desalting (removal of low molecular weight compounds), clarification (removal of particles), and fractionation (protein-protein separation). In this study, we developed an efficient membrane for protein separation based on ceramic nanofibers. Alumina nanofibers were prepared on a porous support and formed large flow passages. The radical changes in membrane structure provided new ceramic membranes with a large porosity (more than 70%) due to the replacement of bulk particles with fine fibers as building components. The pore size had an average of 11 nm and pure water flux was approximately 360 L•h-1•m-2•bar-1. Further surface modification with a self-assembled monolayer of (3-aminopropyl) triethoxysilane enhanced the membrane filtration properties. Characterization with SEM, FTIR, contact angle, and proteins separation tests indicated that the fibril layers uniformly spread on the surface of the porous support. Moreover, the membrane surface was changed from hydrophilic to hydrophobic after silane groups were grafted. It demonstrated that the silane-grafted alumina fiber membrane can reject 100% BSA protein and 92% cellulase protein. It was also able to retain 75% trypsin protein while maintaining a permeation flux of 48 L•h-1•m-2•bar-1.

Preparation of metal-TCNQ charge-transfer complexes on conducting and insulating surfaces by photocrystallization

A generic method for the synthesis of metal-7,7,8,8-tetracyanoquinodimethane (TCNQ) charge-transfer complexes on both conducting and nonconducting substrates is achieved by photoexcitation of TCNQ in acetonitrile in the presence of a sacrificial electron donor and the relevant metal cation. The photochemical reaction leads to reduction of TCNQ to the TCNQ- monoanion. In the presence of Mx+(MeCN), reaction with TCNQ-(MeCN) leads to deposition of Mx+[TCNQ]x crystals onto a solid substrate with morphologies that are dependent on the metal cation. Thus, CuTCNQ phase I photocrystallizes as uniform microrods, KTCNQ as microrods with a random size distribution, AgTCNQ as very long nanowires up to 30 μm in length and with diameters of less than 180 nm, and Co[TCNQ]2(H2O)2 as nanorods and wires. The described charge-transfer complexes have been characterized by optical and scanning electron microscopy and IR and Raman spectroscopy. The CuTCNQ and AgTCNQ complexes are of particular interest for use in memory storage and switching devices. In principle, this simple technique can be employed to generate all classes of metal−TCNQ complexes and opens up the possibility to pattern them in a controlled manner on any type of substrate.

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.

Extensive charge-discharge cycling of lithium metal electrodes achieved using ionic liquid electrolytes

The effect of extended cycling on lithium metal electrodes has been investigated in an ionic liquid electrolyte. Cycling studies were conducted on lithium metal electrodes in a symmetrical Li|electrolyte|Li coin cell configuration for 5000 charge–discharge cycles at a current density of 0.1 mA cm− 2. The voltage–time plots show evidence of some unstable behavior which is attributed to surface reorganization. No evidence for lithium dendrite induced short circuiting was observed. SEM imaging showed morphology changes had occurred but no evidence of needle-like dendrite based growth was found after 5000 charge–discharge cycles. This study suggests that ionic liquid electrolytes can enable next generation battery technologies such as rechargeable lithium-air, in which a safe, reversible lithium electrode is a crucial component.

Probing the effect of charge transfer enhancement in off resonance mode SERS via conjugation of the probe dye between silver nanoparticles and metal substrates

The charge transfer-mediated surface enhanced Raman scattering (SERS) of crystal violet (CV) molecules that were chemically conjugated between partially polarized silver nanoparticles and optically smooth gold and silver substrates has been studied under off-resonant conditions. Tyrosine molecules were used as a reducing agent to convert silver ions into silver nanoparticles where oxidised tyrosine caps the silver nanoparticle surface with its semiquinone group. This binding through the quinone group facilitates charge transfer and results in partially oxidised silver. This establishes a chemical link between the silver nanoparticles and the CV molecules, where the positively charged central carbon of CV molecules can bind to the terminal carboxylate anion of the oxidised tyrosine molecules. After drop casting Ag nanoparticles bound with CV molecules it was found that the free terminal amine groups tend to bind with the underlying substrates. Significantly, only those CV molecules that were chemically conjugated between the partially polarised silver nanoparticles and the underlying gold or silver substrates were found to show SERS under off-resonant conditions. The importance of partial charge transfer at the nanoparticle/capping agent interface and the resultant conjugation of CV molecules to off resonant SERS effects was confirmed by using gold nanoparticles prepared in a similar manner. In this case the capping agent binds to the nanoparticle through the amine group which does not facilitate charge transfer from the gold nanoparticle and under these conditions SERS enhancement in the sandwich configuration was not observed.

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.

Public acceptance towards congestion charge : a case study of Brisbane

This paper investigates public acceptance towards congestion charge in Australia by taking Brisbane as a case study. Public acceptance to congestion charge has often been investigated in the literature. However, few were in the context of an Australian city. This paper fills the gap. A face-to-face survey was conducted to solicit public opinions on the congestion charge, should a congestion charge scheme be implemented in the Brisbane City area. The survey data were analysed to pinpoint important factors relevant to people’s attitudes towards congestion charge and to measure their relationships. Main findings from our analysis are: (1) the residents’ attitudes towards congestion charge differ by genders and by user groups of transport modes; (2) for each of the three groups (i.e., the auto users, the transit riders, and the whole participants), a positive and stable correlation was found between a participant’s attitude towards congestion charge and the effectiveness of congestion charge on reducing traffic congestion. A negative and stable correlation was also found for all three groups between a participant’s attitude towards congestion charge and congestion charge’s negative impact on the attractiveness of working in the city; (3) the auto users tended to be more sceptical about the service capacity of existing transit systems in coping with extra passengers induced by the implementation of congestion charge; and (4) for people with high income, introducing the congestion charge may have no impact on their travelling to the city.

Carbon dioxide capture and gas separation on B80 fullerene

Exploring advanced materials for efficient capture and separation of CO2 is important for CO2 reduction and fuel purification. In this study, we have carried out first-principles density functional theory calculations to investigate CO2, N2, CH4, and H2 adsorption on the amphoteric regioselective B80 fullerene. Based on our calculations, we find that CO2 molecules form strong interactions with the basic sites of the B80 by Lewis acid–base interactions, while there are only weak bindings between the other three gases (N2, CH4, and H2) and the B80 adsorbent. The study also provides insight into the reaction mechanism of capture and separation of CO2 using the electron deficient B80 fullerene.

Order tracking for discrete-random separation in variable speed conditions

The transmission path from the excitation to the measured vibration on the surface of a mechanical system introduces a distortion both in amplitude and in phase. Moreover, in variable speed conditions, the amplification/attenuation and the phase shift, due to the transfer function of the mechanical system, varies in time. This phenomenon reduces the effectiveness of the traditionally tachometer based order tracking, compromising the results of a discrete-random separation performed by a synchronous averaging. In this paper, for the first time, the extent of the distortion is identified both in the time domain and in the order spectrum of the signal, highlighting the consequences for the diagnostics of rotating machinery. A particular focus is given to gears, providing some indications on how to take advantage of the quantification of the disturbance to better tune the techniques developed for the compensation of the distortion. The full theoretical analysis is presented and the results are applied to an experimental case.