1,720,994 research outputs found
Bi2WO6/C-dots/TiO2: A novel z-scheme photocatalyst for the degradation of fluoroquinolone levofloxacin from aqueous medium
Full text link© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Photocatalytic materials and semiconductors of appropriate structural and morphological architectures as well as energy band gaps are materials needed for mitigating current environmental problems, as these materials have the ability to exploit the full spectrum of solar light in several applications. Thus, constructing a Z-scheme heterojunction is an ideal approach to overcoming the limitations of a single component or traditional heterogeneous catalysts for the competent removal of organic chemicals present in wastewater, to mention just one of the areas of application. A Z-scheme catalyst possesses many attributes, including enhanced light-harvesting capacity, strong redox ability and different oxidation and reduction positions. In the present work, a novel ternary Z-scheme photocatalyst, i.e., Bi2WO6/C-dots/TiO2, has been prepared by a facile chemical wet technique. The prepared solar light-driven Z-scheme composite was characterized by many analytical and spectroscopic practices, including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 adsorption–desorption isotherm, Fourier-transform infrared spectroscopy (FT-IR), photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the Bi2WO6/C-dots/TiO2 composite was evaluated by studying the degradation of fluoroquinolone drug, levofloxacin under solar light irradiation. Almost complete (99%) decomposition of the levofloxacin drug was observed in 90 min of sunlight irradiation. The effect of catalyst loading, initial substrate concentration and pH of the reaction was also optimized. The photocatalytic activity of the prepared catalyst was also compared with that of bare Bi2WO6, TiO2 and TiO2/C-dots under optimized conditions. Scavenger radical trap studies and terephthalic acid (TPA) fluorescence technique were done to understand the role of the photo-induced active radical ions that witnessed the decomposition of levofloxacin. Based on these studies, the plausible degradation trail of levofloxacin was proposed and was further supported by LC-MS analysis
Physical Chemistry Examinations
No full textThis book was written to meet the needs and demands of students who find studying physical chemistry a difficult and at times a frustrating experience. The author have observed over several years of teaching this subject at the undergraduate level that students are unrelenting in their desire for so called 'worked examples' and answers to 'typical examination' questions. This book has been prepared primarily to meet this need and assist students at the early years of the undergraduate degree programme in chemistry and chemical engineering understand this subject better and perhaps appreciate the relevance and beauty of the subject as a whole. Worked examples have been provided in every chapter as well as exercises and 'typical examination questions' and solutions to these questions. Care has been taken to ensure that worked examples have been explained in a step by step basis to avoid confusion and misunderstanding on the part of the reader. SI units have been explained throughout and a reasonably good grounding in mathematics is assumed throughout this book. This book is also aimed at the physical chemistry lecturer/teacher who will discover that students are the same everywhere in their desire for 'worked examples', tutorials and solutions to 'typical examination questions'. This book is thus a useful companion to the physical chemistry lecturer and teacher as well as to his/her students. It is not a replacement for a more comprehensive text on the subject and students of physical chemistry are advised to avail themselves of such texts
Process intensification of alkynol semihydrogenation in a tube reactor coated with a Pd/ZnO catalyst
Full text linkSemihydrogenation of 2-methyl-3-butyn-2-ol (MBY) was studied in a 5 m tube reactor wall-coated with a 5 wt% Pd/ZnO catalyst. The system allowed for the excellent selectivity towards the intermediate alkene of 97.8 ± 0.2% at an ambient H2 pressure and a MBY conversion below 90%. The maximum alkene yield reached 94.6% under solvent-free conditions and 96.0% in a 30 vol % MBY aqueous solution. The reactor stability was studied for 80 h on stream with a deactivation rate of only 0.07% per hour. Such a low deactivation rate provides a continuous operation of one month with only a two-fold decrease in catalyst activity and a metal leaching below 1 parts per billion (ppb). The excellent turn-over numbers (TON) of above 105 illustrates a very efficient utilisation of the noble metal inside catalyst-coated tube reactors. When compared to batch operation at 70 °C, the reaction rate in flow reactor can be increased by eight times at a higher reaction temperature, keeping the same product decomposition of about 1% in both cases
Iron sulfide as a sustainable catalyst for the selective hydrogen transfer reduction for the synthesis of fine chemicals
Full text linkPlatinum group metals have been the most widely applied metals for hydrogenation catalysts used in the synthesis of fine chemicals; this has been due to their high catalytic activity and ease of preparation. However, platinum group metal-based catalysts are often overly active in the synthesis of complex molecules with multiple susceptible groups present. The aim of the work in this thesis was to synthesise metal sulfide catalysts for the selective hydrogenation of nitroarenes that are free from platinum group metals.In this work, a simple solvothermal synthesis method was developed to produce a wide range of first row transition metal sulfides. By simply changing the precursor metal salt, the metal sulfide could be precipitated. Additional modifications to the product sulfides were achieved by changing the temperature and capping agent, resulting in a synthesis method by which composition and crystal structure could be modified to produce a range of potential products. Optimisation test work was carried out on the synthesis of FeS2 pyrite and it’s characterisation by powder x-ray diffraction (PXRD) shows a single-phase product under the optimum conditions. Transmission electron microscopy (TEM) shows that the particles obtained are elongated with a width half that of their length which is between ca. 3-5 nm. The catalytic activity of these metal sulfides was characterised by their application in a heterogeneous hydrogen transfer reduction of substituted nitroarenes for the synthesis of substituted anilines. FeS2 pyrite showed excellent catalytic activity towards the hydrogen transfer reduction of nitroarenes. Reaction conditions for the hydrogen transfer reaction were optimised before testing other potential sulfide catalysts. NiS2 pyrite showed no catalytic activity when applied to the hydrogen transfer reaction. This was theorised to be due to the relatively small energy difference in Fe oxidation states allowing for chemical reactions to occur at low energy on the catalyst not present for Ni. FeS2 pyrite was applied to other substituted nitroarenes to determine the broad applicability of the catalyst. FeS2 pyrite maintained a high level of conversion of the substrate material with complete selectivity towards the aniline product. Other hydrogen donors are also explored
Iron sulfide as a sustainable catalyst for the selective hydrogen transfer reduction for the synthesis of fine chemicals
Full text linkPlatinum group metals have been the most widely applied metals for hydrogenation catalysts used in the synthesis of fine chemicals; this has been due to their high catalytic activity and ease of preparation. However, platinum group metal-based catalysts are often overly active in the synthesis of complex molecules with multiple susceptible groups present. The aim of the work in this thesis was to synthesise metal sulfide catalysts for the selective hydrogenation of nitroarenes that are free from platinum group metals.In this work, a simple solvothermal synthesis method was developed to produce a wide range of first row transition metal sulfides. By simply changing the precursor metal salt, the metal sulfide could be precipitated. Additional modifications to the product sulfides were achieved by changing the temperature and capping agent, resulting in a synthesis method by which composition and crystal structure could be modified to produce a range of potential products. Optimisation test work was carried out on the synthesis of FeS2 pyrite and it’s characterisation by powder x-ray diffraction (PXRD) shows a single-phase product under the optimum conditions. Transmission electron microscopy (TEM) shows that the particles obtained are elongated with a width half that of their length which is between ca. 3-5 nm. The catalytic activity of these metal sulfides was characterised by their application in a heterogeneous hydrogen transfer reduction of substituted nitroarenes for the synthesis of substituted anilines. FeS2 pyrite showed excellent catalytic activity towards the hydrogen transfer reduction of nitroarenes. Reaction conditions for the hydrogen transfer reaction were optimised before testing other potential sulfide catalysts. NiS2 pyrite showed no catalytic activity when applied to the hydrogen transfer reaction. This was theorised to be due to the relatively small energy difference in Fe oxidation states allowing for chemical reactions to occur at low energy on the catalyst not present for Ni. FeS2 pyrite was applied to other substituted nitroarenes to determine the broad applicability of the catalyst. FeS2 pyrite maintained a high level of conversion of the substrate material with complete selectivity towards the aniline product. Other hydrogen donors are also explored
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Study of hydrogen liquefaction process through modelling and simulation
No full textHydrogen is viewed as a promising alternative energy source to reduce dependence on conventional fuels, helping to tackle issues such as environmental challenges (climate changes) coming especially from the energy sector. Storing and delivering hydrogen efficiently can be achieved by converting it into its cryogenic liquid form. However, producing liquid hydrogen in industrial settings is both energy-intensive and costly. Current industrial hydrogen liquefaction plants are built for relatively small-scale operations that require a substantial amount of energy to liquefy hydrogen. As the future demand for hydrogen as an energy carrier grows, there will be a need for large-capacity hydrogen liquefaction plants to meet this demand. To deliver liquid hydrogen as an energy carrier, effective and viable hydrogen liquefaction processes are required. In this view, the thesis presents a study of hydrogen liquefaction process through modelling and simulation. A thorough technical review paper was developed to evaluate the past, current, and future of hydrogen liquefaction, followed by a technical paper on the evaluation of the significance of ortho-para-hydrogen conversion in the hydrogen liquefaction process leading to the development of a novel approach. All studied process concepts were modelled and simulated in Aspen Plus, a comprehensive process simulator, under a steady-state condition. To evaluate the viability, a detailed energy and exergy estimation for the hydrogen liquefaction process (including process subsystems and the process equipment) was implemented. The implemented hydrogen liquefaction process simulation and model estimations were used for the efficient determination of the hydrogen liquefaction process for both specific energy consumption (SEC), exergy efficiency, and coefficient of performance (COP). Finally, a 100 TPD capacity of hydrogen liquefaction process was developed which adopted a Claude Cycle of high-pressure hydrogen with Joule-Brayton and Mixed-refrigerant precooling. The hydrogen liquefaction process developed reduces the SEC of an average developed hydrogen liquefaction model (like that of Linde AG Plant) by nearly 70% to about 3.263 kWh/kgLH2, increases the exergy efficiency to 95.85%, and produces a COP of 0.3878. The results presented in this work are anticipated to substantially lead to reducing the cost of hydrogen liquefaction and enable hydrogen as the fuel of the future
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