Thermal stability of mesoscopic compounds of cetyltrimethylammonium and Keggin metatungstates

© 2017 The Royal Society of Chemistry. A hybrid surfactant/polyoxometalate compound was synthesized by combining isopolytungstate anions with the cationic surfactant cetyltrimethylammonium bromide (CTA-Br) to produce a hierarchical compound that we identify as (CTA)7[H2W12O40]Cl·2H2O. At room temperature the compound consisted of hexagonally ordered sheets of Keggin ions, with an intervening gallery containing alkyl-chains of the organic cations. The synthesis was highly dependent on solution pH, reaction time and the order in which the reactants were added. We examined the effect of temperature on the stability of (CTA)7[H2W12O40]Cl·2H2O using thermal gravimetric analysis, differential scanning calorimetry, FT-IR spectroscopy and in situ synchrotron X-ray diffraction, and found a step-wise conversion to monoclinic WOxvia a series of intermediates. Heating under nitrogen atmospheres accelerated transition events by ∼100 °C when compared to heating in air. During heating, the interplanar gallery at first expanded in a series of steps starting at 90 °C as the CTA+ amphiphiles changed orientation, before collapsing rapidly at 240 °C, a temperature coinciding with the removal of about 40% of the organic material. Between 240 and 320 °C, the material consisted of fragments of the Keggin ion cores, arranged in 2D hexagonally-packed sheets. At ∼330 °C, the Keggin ions were completely destroyed and replaced by bulk W17O47 which, upon further heating, transformed to bulk WO2 or WO3 depending on the environment

X-ray-induced reduction of a surfactant/polyoxotungstate hybrid compound

© 2018 John Wiley & Sons, Ltd. We investigate the spontaneous reduction of a photochromic surfactant/polyoxotungstate hybrid during repeated X-ray photoelectron spectroscopy (XPS) scans and show how this effect may confound attempts to use soft X-rays to characterise materials of this nature. The W4f core-level spectra revealed a progressive increase of W5+ and W4+ species at the expense of W6+ as irradiation time increased. The samples developed a blue colour attributed to the presence of W4+ and/or W5+. The progressive photoreduction is also associated with a shift of the W6+ peak within the W4f spectrum to lower binding energies. This work highlights the need to consider inadvertent changes in oxidation state during X-ray photoelectron spectroscopy characterisation of samples containing photoreducible transition metals

Thermal and photo stability of tungsten polyoxometalate-surfactant hybrid compounds

University of Technology Sydney. Faculty of Science.Inorganic-organic polyoxometalate-hybrid materials have attracted increased interest from researchers in recent years due their favourable photo-redox properties. These compounds have the potential to serve in a wide range of applications including photo-catalysis, gas-sensing and medicine. However, limited thermal and photo-chemical stability of these systems has restricted further development into other applications, such as photochromic technologies. This thesis focuses on the synthesis and thermal and photochemical stability of the polyoxometalate-hybrid designated CTA-W₁₂, formed from the metatungstate anion, [H₂W₁₂O₄₀]⁶⁻ and the cationic surfactant cetyltrimethylammonium, (C₁₆H₃₃)N(CH₃)₃⁺ (CTA⁺). Only a narrow window of synthesis conditions actually leads to the production of the studied material because the products produced are very sensitive to pH, temperature, sequence of reactions steps and time. The CTA-W₁₂ exhibits a lamellar bilayer structure, consisting of 2D sheets of hexagonally arranged polyoxometalate anions separated by interdigitated surfactant alkyl-tails. The thermal stability of CTA-W₁₂ was studied using a battery of techniques, including in situ synchrotron x-ray diffraction. It was found that the salt went through seven phase and/or chemical transitions from room-temperature to 800°C within the enclosed environment of the quartz capillary. The lamellar structure persisted for the first three transitions and was destroyed by the fifth at 230°C, when the polyoxometalates fragmented and assumed a hexagonally-close-packed (HCP) arrangement. By ~350°C, the fragments reorganized into the bulk tungsten-suboxide W₁₇O₄₇ and by ~550°C all organic material was removed from the sample. At ~600°C the sample underwent a final transition to monoclinic WO₂. The HCP fifth phase was further studied due to its high crystallinity and was found to be comprised of two types of polyanion fragments, alluding to the complex decomposition kinetics of polyoxometalates and inorganic-organic hybrids. The photochromism of CTA-W₁₂ highlighted the photochemical instability of the inorganic-organic polyoxometalate hybrid. Multiple cycles of irradiation followed by recovery were applied to elucidate the behaviour of the material. The first four photochromic cycles coincided with a slight discoloration of the bleached state, detrimentally affecting photochromic performance slightly. This was ascribed to irreversible oxidation to organic CTA⁺ which caused a yellowing of the material, as well the production of long-lived W⁵⁺ sites deep within the material which could not be re-oxidized by atmospheric O₂. The material maintained reasonable photochromic performance beyond four cycles, which was attributed to the production of more reversible proton-transfer groups, as compared to CH_2/3, and an equilibrium between the production of long-lived W⁵⁺ sites and the diffusion of O₂ into the material. Lattice expansion and amorphization (which was partially reversed during bleaching) was observed to mutually occur with photo-colouration, as evidenced by XRD. The accumulation of strain in the sample, as indicated by the expansion in lattice parameter along the [001] direction, may represent a new photomechanical phenomenon. The photochemical instability of CTA-W₁₂ was further revealed during XPS measurements, which caused progressive reduction of tungsten centres with each successive measurement due to the ionizing effect of the X-ray radiation in combination with the high vacuum environment of the instrument. The project has provided detailed insight into the synthesis, thermal stability and photochemical properties of CTA-W₁₂. The mechanism of photochromism, and the reasons for its partial irreversibility, were found. A new photomechanical phenomenon was uncovered and investigated. The new insights provided by the project will facilitate future attempts to develop applications for these and related inorganic-organic hybrid compounds

Guía de buenas prácticas de producción en la Acuicultura Orgánica para unidades productivas de pequeña y mediana escala

La producción orgánica es un sistema holístico de gestión sostenible de la producción. Dicho sistema, emplea “Buenas Prácticas” de gestión, mediante métodos culturales, biológicos y mecánicos que fomentan y mejoran la salud del agrosistema, la biodiversidad, los ciclos biológicos y la actividad biológica del suelo (Codex). En lo que se refiere a las Buenas Prácticas que implican la producción orgánica en la acuicultura, aparecen como una elección fundamental ya que tiene en cuenta diversos factores como: La elección de especies que no supongan una amenaza para otras especies silvestres; las prácticas en la acuicultura, incluidas la alimentación; el diseño de las instalaciones; la carga animal y la calidad del agua, que deberán ajustarse a las necesidades de desarrollo y fisiológicas de cada especie, como así también de comportamiento; la capacitación del personal encargado del cuidado de los animales que deberá adquirir conocimientos básicos sobre las condiciones para mantener su sanidad y bienestar. Otro aspecto fundamental es la preservación del ambiente acuático, la calidad del agua circundante y la biodiversidad. Por otra parte las producciones ecológicas, tienen como requisito el uso eficiente del agua y la energía en el sistema de gestión empleado. La guía sobre Buenas Prácticas de Producción en la Acuicultura Orgánica tiene como objetivo brindar a los pequeños y medianos productores el conocimiento de aquellos aspectos que se deben tener en cuenta para cumplir con las Buenas Prácticas de Producción en la Acuicultura Orgánica, a los fines que cuenten con una herramienta útil para su implementación.Facultad de Ciencias Veterinaria

Translation in Conversation

This article started with an invitation from the editors to share reflections on translations and, in particular, how academic scholarship gets rearticulated across a variety of audiences. The editors asked us to experiment with new formats for conversation such as passing thoughts back and forth, eliciting responses and explorations. The following text comes from one such experiment inform: an asynchronous exchange that spanned many months and 10 time zones

Metáforas conceituais para design de hipermídias

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão, Programa de Pós-Graduação em Design e Expressão Gráfica, Florianópolis, 2014A eficácia do design de hipermídias é dependente de muitos fatores, incluindo as abordagens de design e métodos seguidos. A era do desenvolvimento ágil trouxe problemas para as equipes de desenvolvimento que precisam criar rapidamente interfaces gráficas para hipermídias, o que fomentou o interesse na integração do design de experiência do usuário e desenvolvimento ágil. Devido a isso, um processo chamado "Rapid Metaphor Processing? foi proposto para auxiliar o desenvolvimento rápido de interfaces gráficas para hipermídias. Inicialmente, a teoria de Metáforas conceituais é analisada, remontando autores que indicam ser este um aspecto imperativo para a comunicação e interação humana com hipermídias. Uma abordagem baseada neste conceito é então definida como um processo de projeto, sob a hipótese de que é possível, com a manutenção paralela de um senso de design centrado no usuário, agilizar soluções criativas. O processo então foi aplicado em um workshop, em quatro diferentes projetos que utilizaram o sistema proposto para desenvolver hipermídias, tendo como objetivo analisar se o processo poderia melhorar a agilidade, o design centrado no usuário e a inovação dos produtos. Implicações de cada conceito são discutidas em detalhes para mostrar a importância e o valor do processo proposto para o processo global de design. Os dados sobre o uso do processo foram obtidos através de questionários pré e pós-workshop realizados com os participantes; bem como da observação do andamento do workshop e da análise da produção resultante. Verificou-se que o processo proposto amplia a velocidade de projetos de experiência do usuário para interfaces gráficas, ao mesmo tempo, promovendo a inovação e o design centrado no usuário.The effectiveness of the hypermedia design is dependent on many factors, including the design approaches and followed methods. The era of agile development has brought problems for development teams that need to quickly create graphical interfaces for hypermedia, which fostered the interest in the integration of user experience design and agile development. Because of this, a process called "Rapid Metaphor Processing" was proposed to aid the rapid development of graphical interfaces for hypermedia. Initially, the theory of conceptual metaphors is reviewed, tracing authors who indicate that this is an imperative aspect for communication and human interaction with hypermedia. An approach based on this concept is then defined as a design process, under the assumption that it is possible, with the parallel maintaining a sense of user-centered design, to streamline creative solutions. The process was then applied in a workshop in four different projects that used the proposed system to develop hypermedias, aiming to examine whether the process could improve the agility, the user-centered design and product innovation. Implications of each concept are discussed in detail to show the importance and value of the proposed process for the global design process. Data on the use of the process were obtained through pre and post workshop questionnaires conducted with the participants; as well as the observation of the progress of the workshop and analysis of the resulting products. It was found that the proposed method enhances the speed of user experience designs for graphical interfaces, while fostering innovation and user-centered design