Metallophthalocyanine-based molecular materials as catalysts for electrochemical reactions
- Authors: Zagal, José H , Griveau, Sophie J , Silva, Francisco , Nyokong, Tebello , Bedioui, Fethi
- Date: 2010
- Language: English
- Type: text , Article
- Identifier: vital:7239 , http://hdl.handle.net/10962/d1019718
- Description: Metallophthalocyanines confined on the surface of electrodes are active catalysts for a large variety of electrochemical reactions and electrode surfaces modified by these complexes can be obtained by simple adsorption on graphite and carbon. However, more stable electrodes can be achieved by coating their surfaces with electropolymerized layers of the complexes, that show similar activity than their monomer counterparts. In all cases, fundamental studies carried out with adsorbed layers of these complexes have shown that the redox potential is a very good reactivity index for predicting the catalytic activity of the complexes. Volcano-shaped correlations have been found between the electrocatalytic activity (as log I at constant E) versus the Co(II)/(I) formal potential (E°′) of Co-macrocyclics for the oxidation of several thiols, hydrazine and glucose. For the electroreduction of O2 only linear correlations between the electrocatalytic activity versus the M(III)/M(II) formal potential have been found using Cr, Mn, Fe and Co phthalocyanines but it is likely that these correlations are “incomplete volcano” correlations. The volcano correlations strongly suggest that E°′, the formal potential of the complex needs to be in a rather narrow potential window for achieving maximum activity, probably corresponding to surface coverages of an M-molecule adduct equal to 0.5 and to standard free energies of adsorption of the reacting molecule on the complex active site equal to zero. These results indicate that the catalytic activity of metallophthalocyanines for the oxidation of several molecules can be “tuned” by manipulating the E°′ formal potential, using proper groups on the macrocyclic ligand. This review emphasizes once more that metallophthalocyanines are extremely versatile materials with many applications in electrocatalysis, electroanalysis, just to mention a few, and they provide very good models for testing their catalytic activity for several reactions. Even though the earlier applications of these complexes were focused on providing active materials for electroreduction of O2, for making active cathodes for fuel cells, the main trend in the literature nowadays is to use these complexes for making active electrodes for electrochemical sensors. , Original publication is available at http://dx.doi.org/10.1016/j.ccr.2010.05.001
- Full Text: false
- Date Issued: 2010
Laser surface hardening of AISI 1518 alloy steel
- Authors: Zhang, Tao
- Date: 2010
- Subjects: Lasers , Laser beams , Lasers in engineering , Nd-YAG lasers , Steel alloys , Surfaces -- Effect of radiation on
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9613 , http://hdl.handle.net/10948/723 , Lasers , Laser beams , Lasers in engineering , Nd-YAG lasers , Steel alloys , Surfaces -- Effect of radiation on
- Description: The laser surface hardening process will enhance the hardness profile of automotive components and ensure better process control and predictability of quality as compared to the conventional hardening processes. A 2KW Nd-YAG laser system was used to harden the surface of alloy steel with various process parameters (laser power, focal spot diameter and beam velocity). The results (microhardness, microstructure change and residual stress distribution) were measured and analyzed with Vickers microhardness tester, optical/electron microscope and hole-drilling residual stress equipment. Statistical analyses of the experimental data were used for explaining the relationships between process parameters, microhardness and microstructure. General thermal hardening was applied in the research to show the influence of heating temperature and cooling method on microstructure and mechanical properties. Also, the results were compared with laser surface hardening process from microhardness, microstructure and residual stress to show the advantage of laser surface hardening. Through analysis of the results of the laser surface hardening experiments, a suitable laser power density and interaction time for optimum hardening was obtained. The presented laser surface hardening process can also be applied to other alloy steel surface hardening process.
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- Date Issued: 2010
Microbial ecology of the Buffalo River in response to water quality changes
- Authors: Zuma, Bongumusa Msizi
- Date: 2010
- Subjects: Water quality -- South Africa -- Buffalo River (Eastern Cape) , Microbial ecology -- South Africa -- Buffalo River (Eastern Cape) , River Health Programme (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:6038 , http://hdl.handle.net/10962/d1006182 , Water quality -- South Africa -- Buffalo River (Eastern Cape) , Microbial ecology -- South Africa -- Buffalo River (Eastern Cape) , River Health Programme (South Africa)
- Description: South Africa’s freshwater quality and quantity is declining and consequently impacting on the ecological health of these ecosystems, due to increased agricultural, urban and industrial developments. The River Health Programme (RHP) was designed for monitoring and assessing the ecological health of freshwater ecosystems in South Africa, in order to effectively manage these aquatic resources. The RHP utilises biological indicators such as in-stream biota as a structured and sensitive tool for assessing ecosystem health. Although the RHP has been widely implemented across South Africa, no attempts have been made to explore microbial ecology as a tool that could be included as one of the RHP indices. This study used selected microbial responses and water physico-chemical parameters to assess the current water quality status of the Buffalo River. This study showed that water quality impairments compounded in the urban regions of King William’s Town and Zwelitsha and also downstream of the Bridle Drift Dam. The results also showed that the lower and the upper catchments of the Buffalo River were not significantly different in terms of water physico-chemistry and microbiology, as indicated by low stress levels of an NMDS plot. Though similarities were recorded between impacted and reference sites, the results strongly showed that known impacted sites recorded the poorest water physico-chemistry, including the Yellowwoods River. However, the Laing Dam provided a buffer effect on contributions of the Yellowwoods River into the Buffalo River. Multivariate analysis showed that microbial cell counts were not influenced by water physico-chemical changes, whilst microbial activity from the water and biofilm habitats showed significant correlation levels to water physico-chemical changes. This study demonstrated that further investigations towards exploitation of microbial activity responses to water physico-chemical quality changes should be channelled towards the development of microbiological assessment index for inclusion in the RHP.
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- Date Issued: 2010
A study of parental participation in school governance in selected high schools : Zwelitsha Township, Province of the Eastern Cape
- Authors: Zuma, Nandipha
- Date: 2010
- Subjects: School management and organization -- Parent participation -- South Africa -- Eastern Cape , High schools -- South Africa -- Eastern Cape -- Administration
- Language: English
- Type: Thesis , Masters , MPA
- Identifier: vital:8165 , http://hdl.handle.net/10948/1305 , School management and organization -- Parent participation -- South Africa -- Eastern Cape , High schools -- South Africa -- Eastern Cape -- Administration
- Description: This study investigates parental involvement in school governance in selected high schools in Zwelitsha, King Williams Town District in the Eastern Cape Province. The research study was conducted in three high schools in Zwelitsha Township. These schools are Nompendulo Senior Secondary, Thembalabantu High School and Xolani Senior Secondary School. Questionnaires were designed and distributed to the principals, educators and parents whose children are learners in these schools. The interview questions were designed and distributed to parents whose children are learners in these selected schools, educators and school principals and members of the school governing body from each school. Respondents were asked about the levels of parental involvement in their schools, parents’ awareness of school governance and the relationship between schools and communities. However, the objectives of the study were to: Assess parental involvement in school governance in selected high schools in Zwelitsha, King Williams Town District in the Province of the Eastern Cape; To determine the nature and extent of parental participation in school academic activities; To examine the role of parents in the school governing body; To determine measures that can be taken to encourage the participation of parents in school governance These objectives have been achieved by providing empirical evidences which shows that the levels of parental involvement in the previously disadvantaged high schools are very low. This is related to the parents’ level of education. Parents who are literate are more involved than those are illiterate. This research also reveals that high v. levels of working parents contributes to the low levels of parental involvement in school governance. Most parents in this area know nothing about school governance and those that are aware are not keen to be involved. The class structure of the society has an influence in the participation of parents in school governance. Parents’ meetings that are held on Sunday afternoon are a challenge to parents that come from the villages outside Zwelitsha because of the scarcity of transport on this day. and these situations discourage them from being actively involved in their children’s education. The study provides the factors that cause non-involvement of parents in school governance. Subsequently, the following strategies for participation of parents in school governance were given: Capacitating of parents Establishment of teacher-parent collegiality Recognition of cultural capital Establishment of parent organisations Utilisation of non-governmental organisations Establishment of centres of learning. This study also indicates the following strategies that may assist to enhance the parental involvement in school governance: Parents engagement and empowerment Co-operation between schools and parents Collaboration with other community, private and other public institutions Invitation of complaints and welcoming of criticism. In conclusion, the findings provide clear indication that the participation of parents in school governance is low. Recommendations that could assist the schools to encourage and to enhance parents to participate in school governance are given.
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- Date Issued: 2010
Designing molecular materials and strategies for the electrochemical detection.pdf
- Identifier: http://hdl.handle.net/10962/262592 , vital:53535
- Description: We present an overview of the successes and challenges still faced in the detection of NO, O2˙− and ONOO− in biological media. We provide a full discussion on the electrochemical analyses of each of these species and we summarise the significant research contributions towards the development of sensors for individual and simultaneous detection of these species. We emphasize the importance of understanding the potential interferents in developing such sensors. We show that significant advances have been made with regard to the detection of NO in biological media leading to the development of marketable NO sensors, though there is room for improvement in terms of interferences. A brief outlook into the future perspectives of the use of a multi-electrochemical array sensor for simultaneous detection of NO, O2˙− and ONOO− is presented.
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- Date Issued: 2010