1,720,962 research outputs found
PHOTOCATALYTIC APPLICATIONS OF TiO\u3csub\u3e2\u3c/sub\u3e FOR CATECHOL DEGRADATION AND α-Fe\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e FOR CARBON DIOXIDE REDUCTION AT AIR-SOLID INTERFACE
No full textNatural and anthropogenic processes are emitting organic and inorganic pollutants, such as phenolic compounds, carbon dioxide (CO2), etc. in the atmosphere, which are increasing with time. In addition, to meet the energy demand of world’s growing population using nonrenewable fossil fuels are causing its depletion. Therefore, development of new technologies that can minimize atmospheric pollution and contribute to energy demand is imperative. Many methods or technologies have been developed for addressing those issues so far including advanced oxidation process, anaerobic biological treatments, and photocatalytic process. Among them, heterogenous semiconductor photocatalysis possesses clean and low-cost methodology and can simultaneously solve the problems of energy and environmental contamination. In this thesis, photocatalytic catechol (model pollutant) degradation with Degussa P25, a mixture of anatase and rutile phase of titanium dioxide (TiO2) and CO2 reduction with potassium and gallium-doped iron oxide (α-Fe2O3) are reported.
The research uses Degussa P25 to study the degradation of catechol at air-solid interface because of low cost, stability, and abundant sources of TiO2. Catechol forms a chelate with TiO2 and shows absorption band in visible range through ligand-to-metal charge-transfer (LMCT) transition. The photocatalytic activity of catechol degradation on TiO2 surface are reported irradiating at λcut-off ≥ 320 nm, 400 nm, and 515 nm. The generation of reactive oxygen species (hydroxyl radical, superoxide anion radical, singlet oxygen) and redox pairs has been studied with scavengers. The chemical fates of scavengers and selectivity are also reported. Finally, the apparent quantum efficiency (AQE) for catechol loss and CO2 and carbon monoxide (CO) growths are determined.
The amount of CO2 in the atmosphere can be minimized by reducing it to useful fuels photocatalytically. Potassium-doped iron oxide materials of varying potassium compositions (100 Fe:x K, 0 ≤ x ≤ 5) and calcination temperatures (400 °C, 500 °C, 600 °C, 700 °C, and 800 °C) are synthesized using incipient wetness impregnation method. The structure, composition, and properties of the catalysts are investigated by X-ray diffraction, thermal analysis and multiple spectroscopies, including: DRUV-vis, FTIR, Raman, ICP-AES, XPS and UPS, TEM with EDS and SAED. UV-visible light (λcut-off ≥ 295 nm) excites the catalysts in presence of pure CO2 or air (400 ppm CO2), both under a saturated water vapor atmosphere. The AQE for the CO(g) production shows maximum for 100 Fe:1 K. The surface-doped potassium photocatalyst enhances the photocatalytic efficiency by creating a more negative conduction band than the CO2/CO reduction potential. The role of potassium and nitrate has been explored. We also synthesize gallium-doped iron oxide using precipitation method with varying gallium compositions (100 Fe:x Ga, 0 ≤ x ≤ 5). The photocatalytic experiment similar to that of potassium-doped catalysts are performed. The material, 100 Fe:2 Ga shows greater reactivity creating a great scope for future studies.
The studies of pollutant degradation and CO2 reduction with TiO2 and α-Fe2O3, respectively at air-solid interface provides a pathway to minimize the atmospheric pollution and contribute to the energy. They create a path to study more for other applications in air purification, water splitting, fuel production, etc. and development of efficient semiconductor photocatalyst
Advanced Heteroatom Doped Nanocarbon Materials as Platinum Catalyst Supports for Fuel Cells
No full textThe pressing demand for high performance, operationally stable and inexpensive electrocatalyst materials for proton exchange membrane fuel cells (PEMFCs) has spurred significant research and development interest in this field. Until now, fuel cells based on commercially available Pt/C electrocatalysts have not met some of the technical challenges to the widespread commercial adoption of PEMFCs. The main issues associated with the commercial validity of PEMFCs are the high cost and inadequate long term operational stability of Pt/C catalysts typically used to facilitate the inherently sluggish oxygen reduction reaction (ORR). Therefore, the replacement of Pt/C with novel and more effective catalyst materials is critical. These expensive precious metal catalysts make up a large portion of the overall PEMFC stack cost and suffer degradation under harsh potentiodynamic conditions. Therefore, careful electrocatalyst design strategies must be developed to reduce the cost of ORR catalysts with sufficient activity and stability to meet the technical targets set for the use of PEMFCs.
In this work, two approaches are applied to develop new electrocatalyst materials for PEMFCs. The first is to design unique sulfur-doped graphene (SG) and sulfur-doped CNT (S-CNT) supports with the objective of replacing the traditional carbon black to enhance stability toward carbon corrosion. The second is to deposit Pt nanoparticles and nanowires onto SG and S-CNT with the objective of exceeding the activity and stability possible with conventional catalysts. These two catalyst technologies are developed with the ultimate objective of integrating the Pt electrodes into membrane electrode assembly (MEA) to provide excellent PEMFC performance.
The first study focuses on the use of SG prepared by a thermal shock/quench anneal process as a unique Pt nanoparticle support (Pt/SG). These materials are subjected to a variety of physicochemical characterizations and electrochemical investigation for the ORR. Based on half-cell electrochemical testing in acidic electrolyte, Pt/SG demonstrated increased ORR activity and unprecedented stability over the state-of-the-art commercial Pt/C, maintaining 87% of its electrochemically active surface area following accelerated durability testing. Density functional theory (DFT) calculations highlighted that the interactions between Pt and graphene are enhanced significantly by sulfur doping, leading to a tethering effect that can explain the outstanding electrochemical stability. Furthermore, sulfur dopants resulted in a downshift of the Pt d-band center, explaining the excellent ORR activity and rendering SG as a new and highly promising class of catalyst supports for electrochemical energy technology and PEMFCs.
The beneficial impacts of SG support can be utilized by growing more stable nanostructures such as Pt nanowires on SG to further improve the activity and stability of Pt catalysts. Toward this end, we carried out the direct growth of platinum nanowires on SG (PtNW/SG) by a simple, surfactant free solvothermal technique. The growth mechanism, including Pt nanoparticle nucleation on SG, followed by nanoparticle attachment with orientation along the direction is also highlighted. PtNW/SG demonstrated increased Pt mass activity and a specific activity that is 188% higher than state-of-the-art commercial Pt/C catalysts. Most notably, under a harsh potentiodynamic condition (potential cycles: 3000, potential range: 0.05 to 1.5 V vs RHE), PtNW/SG retained 58% of its electrochemically active surface area and 67% of its ORR activity in comparison to Pt/C that retained less than 1% of its surface area and activity and so failed.
Given the evidence that SG is a promising support for Pt catalysts, the next logical step is to investigate the influence of sulfur on catalytic materials. Accordingly, we study the effects of sulfur on the electrochemical activity and stability of various SG supported platinum nanowires (PtNW/SGs). To investigate the influence of sulfur, a series of SG materials with varying sulfur contents ranging from 0.35 to 3.95 at% are investigated as Pt nanowire catalyst supports. Based on the physico-chemical characterizations, electrochemical measurements and DFT calculations, the amount of sulfur is shown to significantly affect the electrokinetics of the Pt nanowires. The best ORR kinetics are observed for the Pt nanowires supported on graphene with 1.40 at% sulfur. At higher sulfur contents, further enhancements are not observed, and in fact, leads to a loss of activity. At lower sulfur contents, the beneficial role of sulfur does not have a marked impact on performance so that the characteristics and performance more closely resemble that obtained with undoped graphene supports.
Obviously, the beneficial effect of sulfur dopant species can be utilized by doping sulfur into other types of carbon supports such as CNT (S-CNT). Finally, we report on the synthesis, characterization and electrochemical evaluation of S-CNT-supported Pt nanowires (PtNW/S-CNT). PtNW/S-CNT synthesized by a modified solvothermal method demonstrated an increased mass activity and a specific activity 570% higher than state-of-the-art Pt/C. The stability of PtNW/S-CNT is also shown to be very impressive through accelerated degradation testing. Only insignificant changes to the electrochemically active surface area (ECSA, 93% retention) and mass activity (81% retention) of PtNW/S-CNT are observed over the course of cycling, in contrast to sizable losses observed with commercial Pt/C (<1% retention in ECSA and mass activity) under same conditions
Community-based indigenous tourism, NGOs and indigenous poverty in Bangladesh
No full textIndigenous peoples, with unique cultures and ways of life, often constitute the most vulnerable groups of society and may experience discrimination and marginalisation in many forms. Observing the growing quest to obtain first-hand experiences of indigenous cultures and lifestyles, many indigenous communities around the world have embraced tourism as a way forward for their socio-economic development, primarily to address their poverty. This is evident in the increasing focus on community-based tourism (CBT), indigenous tourism and their application together. Concomitantly, many development-oriented organisations, i.e. donors and NGOs, have incorporated tourism as an additional means of development, explicitly emphasising the inclusion of indigenous and/or host communities within the formal tourism economy. However, the outcomes of such involvement and interventions are sometimes questionable and previous studies in this regard have proved inconclusive, especially in the context of indigenous poverty alleviation in developing countries. This study thus aims to investigate the role of NGOs in alleviating rural indigenous poverty through the facilitation of community-based indigenous tourism (CBIT) involvement in a developing country context - Bangladesh.
Fitting into the domain of critical theory, a qualitative case study approach was adopted where multiple methods, including semi-structured interviews, focus group discussions and observations, were employed to collect empirical evidence from two indigenous communities in Bangladesh. Following this a thematic analysis was applied in analysing the qualitative data collected and developing the key findings.
Findings show that NGO-facilitated tourism involvement has created some economic opportunities (e.g. income and employment, access to credit) that are limited in amount but significant considering the marginal conditions of the communities. Such involvement was to some extent also found to be contributing to the empowerment and reduced economic vulnerability of the communities. Simultaneously, the findings show that these benefits come along with several costs (e.g. creating external dependency, invasion of indigenous privacy, the threat of displacement) that overshadow the positive gains in many cases. The study reveals a dynamic interplay of multidimensional empowerment aspects moving beyond the mere economic aspect. While investigating the research issue, the findings observed a high interdependency between opportunity, empowerment and security. The thesis also examines a range of factors that restrict the indigenous communities (e.g. tensions, seasonality, market constraints, macro-environmental effects) and NGOs (e.g. strategic limitations and activity constraints) in operationalising tourism benefits. Finally, based on the empirical evidence and considering the existence of a development gap, the study concludes that NGO-facilitated tourism involvement (both direct and indirect) can make a contribution to indigenous poverty alleviation; however, this could best be viewed as an additional tool rather than an alternative tool to their traditional livelihood practices.
This thesis contributes to the broader discussion of externally-facilitated tourism involvement for indigenous communities, as well as to the debate over the tourism-indigenous poverty nexus from such involvement. In doing so, the thesis reflects a combination of theoretical, conceptual and methodological contributions with associated practical implications. It incorporates the understanding of the key elements of stakeholder identification and salience theory (power, legitimacy and urgency) along with the poverty alleviation determinants (opportunity, empowerment and security) from the anti-poverty tourism research framework. The study demonstrates the utility of this conjoined conceptual approach that provides a conceptual schema to facilitate and extend our current understanding of the NGO-tourism-indigenous poverty nexus. The thesis also adds to our current understanding of community-based tourism from a non-western research perspective, and revealing the challenges and related opportunities in the conducting of research with indigenous communities, and by non-indigenous researchers
Community-based indigenous tourism, NGOs and indigenous poverty in Bangladesh
Get PDFIndigenous peoples, with unique cultures and ways of life, often constitute the most vulnerable groups of society and may experience discrimination and marginalisation in many forms. Observing the growing quest to obtain first-hand experiences of indigenous cultures and lifestyles, many indigenous communities around the world have embraced tourism as a way forward for their socio-economic development, primarily to address their poverty. This is evident in the increasing focus on community-based tourism (CBT), indigenous tourism and their application together. Concomitantly, many development-oriented organisations, i.e. donors and NGOs, have incorporated tourism as an additional means of development, explicitly emphasising the inclusion of indigenous and/or host communities within the formal tourism economy. However, the outcomes of such involvement and interventions are sometimes questionable and previous studies in this regard have proved inconclusive, especially in the context of indigenous poverty alleviation in developing countries. This study thus aims to investigate the role of NGOs in alleviating rural indigenous poverty through the facilitation of community-based indigenous tourism (CBIT) involvement in a developing country context - Bangladesh.
Fitting into the domain of critical theory, a qualitative case study approach was adopted where multiple methods, including semi-structured interviews, focus group discussions and observations, were employed to collect empirical evidence from two indigenous communities in Bangladesh. Following this a thematic analysis was applied in analysing the qualitative data collected and developing the key findings.
Findings show that NGO-facilitated tourism involvement has created some economic opportunities (e.g. income and employment, access to credit) that are limited in amount but significant considering the marginal conditions of the communities. Such involvement was to some extent also found to be contributing to the empowerment and reduced economic vulnerability of the communities. Simultaneously, the findings show that these benefits come along with several costs (e.g. creating external dependency, invasion of indigenous privacy, the threat of displacement) that overshadow the positive gains in many cases. The study reveals a dynamic interplay of multidimensional empowerment aspects moving beyond the mere economic aspect. While investigating the research issue, the findings observed a high interdependency between opportunity, empowerment and security. The thesis also examines a range of factors that restrict the indigenous communities (e.g. tensions, seasonality, market constraints, macro-environmental effects) and NGOs (e.g. strategic limitations and activity constraints) in operationalising tourism benefits. Finally, based on the empirical evidence and considering the existence of a development gap, the study concludes that NGO-facilitated tourism involvement (both direct and indirect) can make a contribution to indigenous poverty alleviation; however, this could best be viewed as an additional tool rather than an alternative tool to their traditional livelihood practices.
This thesis contributes to the broader discussion of externally-facilitated tourism involvement for indigenous communities, as well as to the debate over the tourism-indigenous poverty nexus from such involvement. In doing so, the thesis reflects a combination of theoretical, conceptual and methodological contributions with associated practical implications. It incorporates the understanding of the key elements of stakeholder identification and salience theory (power, legitimacy and urgency) along with the poverty alleviation determinants (opportunity, empowerment and security) from the anti-poverty tourism research framework. The study demonstrates the utility of this conjoined conceptual approach that provides a conceptual schema to facilitate and extend our current understanding of the NGO-tourism-indigenous poverty nexus. The thesis also adds to our current understanding of community-based tourism from a non-western research perspective, and revealing the challenges and related opportunities in the conducting of research with indigenous communities, and by non-indigenous researchers
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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