Previously, we reported an investigation on Delonix regia dye extract as a natural sensitizer for TiO2/DSC assembled with platinum counter electrode and low power conversion efficiency was recorded. This necessitated the current investigation on Delonix regia dye extract as a natural sensitizer for TiO2/DSCs assembled with different counter electrodes. Platinum counter electrode was used for one of the DSCs while polyaniline (PANI) was used to replace platinum in the other DSC. The vitriol treated PANI thin film consisted of aniline mixed with potassium dichromate directly reacted on circular graphite foam. The conductivity and Hall coefficient were measured to be and respectively using ECOPIA Hall Effect Measurement System (HMS-3000 Version 3.52). Sequel to this, the DSCs were assembled and characterized using a standard overhead Veeco viewpoint solar simulator equipped with AM 1.5 filter to give a solar radiation of 1000 W/m2 and coupled to a Keithley source meter (model 4200SCS) which was connected to the computer via GPIB interface for data acquisition. The overall solar power conversion efficiencies of 0.02% and 0.04% were obtained for TiO2-DSC//Delonix regia dye//platinum electrode and TiO2-DSC//Delonix regia dye//PANI electrode respectively. Delonix regia dye extract proved to be rather a poor sensitizer as can be seen by the low spectral absorption at lower energies with short circuit current density of 0.10mAcm-2 and 0.11mAcm-2 respectively. Nevertheless, a 10% decrease in the electron recombination via redox electrolyte and collection at the photoelectrode was observed for TiO2-DSC//Delonix regia dye//PANI electrode and a 20% increase in the open circuit voltage (Voc) was also observed. Finally, about 37% increase in the fill factor was observed for the TiO2-DSC//Delonix regia dye//PANI electrode over TiO2-DSC//Delonix regia dye//platinum electrode. This necessitated approximately 50% increase in the power conversion efficiency for the TiO2-DSC//Delonix regia dye//PANI electrode over TiO2-DSC//Delonix regia dye//platinum electrode.
In this study, Cu - doped ZnO thin films were prepared at different annealing temperatures from Copper acetate precursor by sol-gel spin coating method for Photocatalytic Applications. The films were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The obtained powders were annealed under air in the range of for Cu – ZnO. The surface morphological, structural, electrical and optical properties of the as-deposited ZnO films have been investigated as a function of Cu-doping level. The thickness of the films was estimated by Fizeau fringes interference method which varied from 195 to 198 nm. The X-ray diffraction analysis indicated that the wurtzite structure was maintained for all samples and copper was successfully doped into ZnO at low TC. However, the formation of monoclinic CuO was observed at higher TC. For Cu – ZnO, the crystallite size increased with the annealing temperature from 15.86 to 24.24 nm. The isotherms obtained were type IV with a hysteresis type H 3, conﬁrming the mesoporous behavior of the catalysts. The surface area was in the range of 35.1 to 8.66 /g. All the prepared catalysts mainly showed two emission regions: a sharp peak in the ultraviolet region and another broad peak in the visible region. The photocatalytic activity was achieved by the degradation of 300 mg/L malachite green (MG) aqueous solution under UV irradiation. The ﬁndings showed that the increased annealing of different concentration of Cu doped ZnO with CuO on the surface resulted in highly improved photocatalytic activity. Various optical constants such as absorbance, transmittance of the films have been studied. The values of transmittance are high in the visible and IR region and it is minimum in the UV region. Absorbance decreases with higher percentage of Cu concentration. The band gap of the films varied 3.21 to 3.05 eV. The resistivity gradually decreases with the increase of temperature, which indicates the semiconducting nature of the materials. Resistivity also increases with the increasing doping concentration. The conductivity decreases with the increasing of Cu concentration.
This paper discusses the issues and challenges of instructional resources for teaching and learning science in Nigeria secondary schools. The concept of instructional resources was treated as well as the relevance of availability and proper usage of instructional resources. The instructional resources discussed in this study were basically material and human resources. The human resources are laboratory staff. The material resources treated among others include: the classroom, the laboratory, library, equipment, models and charts, curriculum and science textbook. The issue of inadequacy and lack of these resources in most secondary schools were discussed. The work also examined the instructional resources and the science teacher. The study concluded that science should be learnt in a way that will equip our students with such attributes as creativity, resourcefulness and manipulative skills in this way it could be meaningful to the learner and also help in the development of entrepreneurial skills for self-reliance. It was therefore, recommended that stakeholders in science education should provider enough funds to build more classrooms, laboratories and provide the equipment and resources for the teaching and learning of science, libraries should be provided with modern quality science textbooks for teachers and students and government should make available adequate fund for provision of instructional resources for teaching science.
Zinc oxide has justifiably been attracting attention in several fields, and the relatively new field of tribology is not left out. Aside from its already extensively researched and documented applications in materials science, semiconductor and electronics industry, zinc oxide nanoparticles and thin films appear to be gaining fast grounds as tribological materials, thereby justifying a zealous approach in further exploring their inherent properties in this area. In this work, zinc oxide thin films were deposited by MOCVD (metal-organic chemical vapour deposition) on soda lime glass and AISI304L stainless steel plates at temperatures of 300°C, 330°C, 360°C, 390°C and 420°C respectively, using anhydrous zinc acetate as the precursor. The carrier gas was air with a flow rate of 2.5 dm3min-1 at atmospheric pressure, and deposition time of 2 hours each. The thickness and tribological properties of the thin films produced were thereafter investigated. The thickness was measured by RBS (Rutherford backscattering spectroscopy) using a 1.7 MeV Tandem Accelerator, and the friction and wear properties were tested with a HFRR (high frequency reciprocating rig) under dry contact conditions, Olympus BH-2 Optical Microscope, and ADE Phase Shift MicroXam Optical Surface Profiler. The thickness was found to decrease with increasing deposition temperature, although for the 300°C deposition temperature there appeared to be a bloated thickness, which is attributable to such factors as incomplete precursor decomposition, turbulence in precursor flow, and energy straggling during RBS measurement. The friction tests highlighted coefficients of friction which were relatively low at the onset of the tests, but thereafter rapidly increased, owing possibly to temperature rise, attendant rapid oxidation and aided abrasion by worn debris. The average coefficient of friction of each test was computed, and the outcome (0.33 – 0.43) for all of them was a material still good enough for use in reducing friction at nanolevel, even with worn out matter and increased working temperature, with no noticeable trend regarding their varied deposition temperatures. Microscope and profilometer profiles vividly showed wear scars with material removal and material transfer. The average wear scar diameters as well as the wear volumes were compiled for both the test balls and the thin films. The result showed a largely correlated trend in the wear scar diameters and the wear volumes, and the thin film deposited at 330°C was the coating with the least wear scars, material removal cum transfer on the test ball and sample. This result is attributed to the enhanced thickness of the sample over the others, apart from sample X1 earlier reported to have a problem in its thickness. This temperature is therefore recommended as the optimum deposition temperature for the best tribologically applicable zinc oxide thin films, using zinc acetate precursor by MOCVD.
Carbon nanotubes have demonstrated their versatility in the manufacture of various devices such as molecular probes, pipes, cables, fibers and springs. Recently, they have been used in cement composites to improve their physical and mechanical properties, but there are still many questions regarding the physical-mechanical behavior that can be achieved in structural concrete. In view of this, the present work aimed at the designing of concrete mixtures with multi-walled carbon nanotubes additions, in order to minimize the unfavorable conditions caused by high absorption limestone aggregates and to improve the mechanical properties compared to regular concretes. Results showed improvements in the microstructural development, compressive strength (7 -11%), splitting tensile strength (14-16%) and modulus of elasticity of the concrete (8-12%). However, some issues related to the functionalization and dispersion of the nanotubes in the mixtures remain to be solved to advance their utilization.