Indigenous natural dyes for Gratzel solar cells : Sepia melanin

Dye-sensitized Solar Cells (DSSC), also known as Grätzel cells, have been identified as a cost-effective, easy-to-manufacture alternative to conventional solar cells. While mimicking natural photosynthesis, they are currently the most efficient third-generation solar technology available. Among others, their cost is dominated by the synthetic dye which consists of efficient Ruthenium based complexes due to their high and wide spectral absorbance. However, the severe toxicity, sophisticated preparation techniques as well as the elevated total cost of the sensitizing dye is of concern. Consequently, the current global trend in the field focuses on the exploitation of alternative organic dyes such as natural dyes which have been studied intensively. The main attractive features of natural dyes are their availability, environmental friendly, less toxicity, less polluting and low in cost. This contribution reports on the possibility of using sepia melanin dye for such DSSC application in replacement of standard costly ruthenium dyes. The sepia melanin polymer has interesting properties such as a considerable spectral absorbance width due to the high degree of conjugation of the molecule. This polymer is capable of absorbing light quantum, both at low and high energies ranging from the infrared to the UV region. The comprehensive literature survey on Grätzel solar cells, its operating principle, as well as its sensitization by natural dyes focusing on sepia melanin has been provided in this master’s dissertation. The obtained results in investigating the morphology, chemical composition, crystalline structure as well as optical properties of sepia melanin samples using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy x-ray diffraction, X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Raman spectroscopy, UV-VIS absorption spectroscopy as well as Photoluminescence (PL) for Grätzel solar cell application have been reported. These results represent an important step forward in defining the structure of melanin. The results clearly show that sepia melanin can be used as natural dye to DSSC sensitization. It is promising for the realization of high cell performance, low-cost production, and non-toxicity. It should be emphasized here that natural dyes from food are better for human health than synthetic dyes.Physics1 online resource (xii, 101 leaves) : illustrationsM. Sc. (Physics

Tutors’ perceptions about science curriculum reforms and challenges for their implementation in Teacher Training Colleges in Rwanda

This paper reports science tutors’ perceptions about science curriculum reforms occurred in Rwanda from 1996 to 2013 in Teacher Training Colleges (TTCs). It also highlights their perceptions about challenges and factors for effective implementation of Integrated Science Curriculum (ISC). Data for the study were collected from 26 science tutors teaching ISC in 11 TTCs from 4 provinces using questionnaires and structured interviews. Results showed that a slim majority of science tutors were not resistant to curriculum reform. Even if most of the science tutors were confident while teaching most of the topics in ISC, they have experienced some difficulties in teaching physics and cross-cutting domains related topics as well as practical activities. Other identified challenges include lack of qualified tutors to teach ISC in TTCs, insufficient contact hours allocated to ISC topics, tutors’ heavy workload, lack of sufficient science laboratory equipment and materials. In addition to TTC libraries that are not well equipped, lack of textbooks and teacher’s guides, as well as lack of in-service tutors’ training, were stressed to be some of the challenges. Even if it was found that most competencies, skills, knowledge and attitudes gained by student-teachers after completing ISC were highly rated by science tutors, communication skills and problem-solving skills that are claimed to be important skills needed by graduates of science in the workplaces were poorly rated. The recommended strategies to overcome the identified challenges include active involvement of TTCs’ science tutors in designing and development of ISC. Moreover, all TTCs should be provided with qualified science tutors to teach ISC. Training for in-service science tutors, recruitment of qualified tutors, and provision of adequate facilities, libraries and well-equipped science laboratories for all TTCs are also recommended

Reforms in science curricula in last six decades: Special reference to physics

This review paper discusses the reforms in science curricula particularly those related to physics curricula which took place after the launch of the Sputnik by the Soviet Union in 1957. These reforms have started at national level as well as international level by establishing curriculum facilities around the end of 1960s. This review informs science educators about previous research in science curricular reforms, the struggles of global physics instruction transformation starting from United State of America (USA) and United Kingdom (UK), and current science/physics education researches. Recent advances in physics curriculum development, as well as some important science reform programmes that have been done in Africa, are also discussed. The paper also highlights the Competence Based Curriculum developed by the Ministry of Education - Rwanda Education Board. The paper updates science/physics educators on the evaluation of the effectiveness of various instructional methods used in the past facilitating the identification of potential reform approaches to be successful in the future. Some practical recommendations that can be used for effective teaching and learning of science, especially for physics are also outlined

Students’ conceptual understanding of electricity and magnetism and its implications: A review

Physics subject continues to be considered as difficult and unattractive by students. This leads to the development of negative attitudes towards the subject. Electricity and magnetism as one of the most important areas in physics is particularly considered as difficult due to their abstract nature. Different studies on students’ conceptual understanding of electricity and magnetism have been conducted and several instructional strategies for a conceptual change in this subject matter have been provided. However, there are still some persisting misconceptions even after being treated by those suggested instructional strategies. By using diagnostic tests and remedial approaches to sort out learning barriers, there is a possibility that students’ performance might improve, which would likely lead to disappearing these learning barriers and retaining the appropriate concepts over time scales beyond the assessment schedule of individual classes. Therefore, after reporting on the impact of students’ preconceptions on learning, this review paper also highlights some existing studies on students’ misconceptions in electricity and magnetism. The paper also updates physics educators and researchers on some conceptual tests and assessments used to test students’ misconceptions in electricity and magnetism and some suggested strategies for remedying those misconceptions. Some educational implications and practical recommendations for effective teaching and learning in electricity and magnetism are also outlined

Students’ attitudes towards physics in Nine Years Basic Education in Rwanda

This study investigated students’ attitudes towards physics in Nine Year Basic Education (9YBE) in Rwanda. Data were collected from 380 students from Kayonza and Gasabo Districts using a physics attitudes test. Findings illustrated that more than a quarter of participants felt that learning physics is boring. About 39% think that the subject of physics does not relate to the real-world experience. A significant number of participants had negative attitudes towards physics in terms of the effort required for learning. The findings also showed that the overall level for participants in physics problem-solving skills was low. The item-by-item analysis showed that the differences between responses of students from rural schools and their counterparts from urban schools in categories of problem-solving and physics concepts connections and understanding are statistically significant. It was found that many students in rural schools need to know more about the interpretation of a new equation to be able to apply it to a new physics problem

Lesson plan analysis protocol in assessing mathematics and science lessons

Lesson planning is important in an educational setting. This study assessed how Rwandan tutors and teachers prepare lesson plans (LPs) before implementing them in a classroom. We employed a current and standard lesson plan analysis protocol (LPAP) developed by researchers from Rwanda to code data. We collected a representative sample of 119 mathematics and science subject lesson plans from teacher training college tutors and secondary school teachers for analysis to serve its usability. The study results revealed that only 11% of collected LPs were teachable as they were rated in both a good (70-79% scores) and very good (80-89% scores) range of LPAP interpretation. It was also found that the special education needs, lesson approaches, and lesson evaluation components got low mean scores (below 50%). These components were not given appropriate attention in developed LPs. Therefore, this study suggests that tutors and teachers build a quality lesson plan based on the standard LPAP

Teachers’ perceptions towards the utilization of WhatsApp in supporting teaching and learning of chemistry during COVID-19 pandemic in Rwandan secondary schools

This paper reports the results about teachers’ perceptions towards the utilization of WhatsApp in supporting teaching and learning of chemistry during the COVID-19 pandemic in Rwandan selected secondary schools. The collected data by using a survey questionnaire were from 18 chemistry teachers in Nyarugenge and Kicukiro Districts. The findings illustrated that WhatsApp is effective for teaching chemistry and supporting students learning. This application promotes students’ motivation, engagement, collaboration, interaction, participation, and ubiquitous learning. Despite the facilitation of collaboration between teachers and their students while using WhatsApp, the internet connection related problems including its cost and availability were among the hindering factors for effective collaboration for both students and teachers. The lack of smartphones and computers for some students, teachers, parents, or guardians was among the highlighted limitations for the participation of some students. The limited students’ management and their distraction were also highlighted by some teachers. The provision of computers, smartphones, and enough internet connection for all teachers, parents, or guardians were among the proposed potential solutions. To deal with students’ management and distractions while learning via WhatsApp, there should be the follow-up and guidance provided by teachers, guardians, or parents. Chemistry teachers and students are recommended to use WhatsApp as a supporting learning tool due to its added value of providing ubiquitous learning. Parents, boards in charge of education, and other educational stakeholders should integrate WhatsApp in teaching and learning to complement classroom learning

Natural Dye Sensitizer for Grӓtzel Cells: Sepia Melanin

Research Article published by Science and Education Publishing Vol. 3, No. 1, 2015The efficiency of Grätzel cell can be further improved by the anchoring groups, such as COOH to be adsorbed onto the TiO2 surface with a large electronic coupling. Some of the most efficient sensitizers are synthetic dyes including transition metal coordination compounds such as Ruthenium polypyridyl complexes because of their highly efficient metal-to-ligand charge transfer, suitable ground and excited state energy levels with respect to titanium dioxide conduction band energy. They also have intense and wide range absorption in whole visible range. Even if they present such attractive features, their synthesis process is costly and complicated and they are not environment friendly because they contain heavy rare metals which are undesirable from the point of view of environmental conservation aspects. Natural dye can be the best alternative as they have acceptable efficiency in comparison to that one of transition coordination compounds and their extraction can be done by simple procedures from flowers, leaves, fruits, animals and other natural products. Melanin as the major component Sepia Officinalis ink pigment cause strong interactions with the hydroxyl groups of a TiO2. Melanin possesses a broad band absorbance in UV and visible range up to infrared. It also possesses the COOH and OH groups which would be free to bind to the surface of TiO2. Moreover, melanin polymer has interesting properties such as a considerable spectral absorbance width due to the high degree of conjugation of the molecule. This paper reports results from X-ray diffraction (XRD), UV-Vis as well as Raman spectroscopy of sepia melanin for Grätzel cell application

Morphological and Chemical Composition Characterization of Commercial Sepia Melanin

Research Article published by Science and Education Publishing Vol. 3, No. 1, 2015Melanins are difficult to characterize because of their intractable chemical properties and the heterogeneity in their structural features. Melanin pigments, in fact, are composed of many different types of monomeric units that are connected through strong carbon-carbon bonds. Its high insolubility and undefined chemical entities are two obstacles in its complete characterization. The morphological characterization and particle size distribution for sepia melanin by Scanning Electron Microscopy (SEM) on surface structure and Transmission Electron Microscopy (TEM) to confirm the morphology obtained from SEM was done. Both results show that Sepia melanin is formed by many aggregates agglomerated together. These aggregates are formed also by small spherical granules with different size distributions that have been determined using image-J software. The small granule diameter obtained from different TEM and SEM micrographs were 100-200nm. EDS reveals that C and O were the most abundant in sepia melanin with concentration average concentrations of about 57% and 24% respectively. The major compositions of sepia melanin are C, O, Na, Cl, while the minor are Mg, Ca, K, S and N. From TEM micrograph at high resolution, it was possible to measure the distance between polymers layers of sepia melanin using image-J software and it was 0.323 nm = 3.23 Å