Fabrication and Characterization of Cobalt-Pigmented Anodized Zinc for Photocatalytic Application

Population growth and urbanization have led to water scarcity and pollution, which is a health hazard not only to humans but also to the ecosystem in general. This has necessitated coming up with ways of treating water before consumption. Photocatalysis has proved to be one of the most promising cheap techniques that involve chemical utilization of solar energy. TiO2 widely used in photocatalysis absorbs a narrow range of the solar spectrum compared to ZnO. In this regard, this study aimed at preparing and optimizing cobalt-pigmented ZnO, which is applicable in photocatalytic water treatment. The objectives in this study were to fabricate zinc oxide (ZnO) thin films by anodization, pigment the fabricated films with varying cobalt concentrations, characterize the fabricated films optically, and investigate the cobalt-pigmented ZnO’s performance in the methylene blue degradation under UV light irradiation. Mirror-polished zinc plates were sonicated in ethanol and rinsed. Anodization was done at room temperature in 0.5 M oxalic acid at a constant voltage of 10 V for 60 min, and cobalt electrodeposited in the films. Post-deposition treatment was done at 250°C. Optical properties of the films were studied using a UV-VIS- NIR spectrophotometer in the solar range of 300–2500 nm. The photocatalytic activity of the fabricated films was studied in methylene blue solution degradation in the presence of UV light irradiation for 5 h. Cobalt pigmenting was observed to reduce reflectance and optical band gap from 3.34 to 3.10 eV indicating good photocatalytic properties. In this study, ZnO film pigmented with cobalt for 20 s was found to be the most photocatalytic with a rate constant of 0.0317 h−1 and hence had the optimum cobalt concentration for photocatalytic water treatment. This can be applied in small-scale water purification

Venture capital as a mean of innovation financing in conditions of investment climate volatility in Ukraine

The energy conversion efficiency of a conventional pn junction solar cell decreases as the temperature increases, and this may eventually lead to failures in the photovoltaic system, especially if it uses concentrated solar radiation. In this work, we show that spectrally selective reflector (SSR) surfaces can be important for reducing the heat buildup on passively cooled solar cells. We outline a computational scheme for optimizing DC magnetron-sputtered TiO(2):Nb-based SSRs tailored for silicon solar cells and find good agreement of the reflectance with an experimental realization of the optimal SSR. A figure of merit for SSRs has also been derived and applied to the experimental data

Оплата праці як елемент виробничої діяльності

Transparent and conducting thin films of TiO2:Nb were prepared on glass and aluminum substrates by dual-target reactive DC magnetron sputtering in an Ar+O-2 plasma. The Nb content lay between 0 and 4.9 at% as determined by ion beam analyses. X-ray diffraction showed that vacuum annealing at 450 degrees C led to crystallinity and prevalence of the anatase phase. The influence of Nb doping was studied with regard to structural, optical, and electrical data. Optical constants were determined from spectrophotometric recordings for films on glass, and the onset of free-electron behavior was documented for annealed films. The latter films, deposited onto Al2O3-coated Al, were found to display optically selective reflectance and to be useful for solar energy applications

Influence of Deposition Parameters on Optical Properties of Sputtered Tungsten Oxide Films

Thin films of tungsten oxide were deposited on glass substrates at different temperatures and O2/Ar ratios using DC Magnetron sputtering system. The samples were characterized using x-ray diffractometry and spectrophotometer structurally and optically respectively. Analysis of the results reveals dependence of structure on thickness and temperature. The O2/Ar ratio is also found to influence the optical properties appreciably for the entire wavelength range studied. Visual inspection of the films show that O2/Ar ratio influences the coloration of the film which varies from clear to dark blue for high to low O2/Ar ratios respectively

Fabrication and Characterization of Cobalt Pigmented Anodized Zinc for Photocatalytic Application

ZnO is an n-type oxide semiconductor with a direct wide band gap greater than 3 eV. Like any other semiconductor, the optical and electrical characteristics can be influenced by doping or adjusting process conditions which broaden its applications. In this work, varying amounts of Cobalt (0.01g-0.04g) were electrodeposited on anodized Zinc thin films (ZnO) followed by heat treatment to about 2500C. Optical characterization was performed in the range 300-2500 nm to obtain reflectance data which aided in defining the absorption coefficient and band gap of the films. Photocatalytic activity of the films was explored in Methylene Blue solution degradation under UV light irradiation. Analyzed data revealed a band gap shift to the red, i.e. from 3.34 eV to 3.10 eV for pure ZnO and 0.04g-Cobalt pigmented ZnO thin films respectively. Moreover, absorption coefficient increased with pigmentation attributed to the band shrinkage effect which elucidates that ZnO:Co thin films serve as good candidates for application in photocatalysis. All the fabricated films were photocatalytic but ZnO thin films containing 0.02g of Cobalt was the most photocatalytic

Contribution of Drude and Brendel Model Terms to the Dielectric Function; A case of TiO2:Nb Thin Films

Parametric modeling provides a mean of deeper understanding to the properties of materials. Dielectric function is one of the key parameters which can provide information on the dielectric nature of a thin film or bulk materials. It can be obtained by modeling the material using appropriate existing, new or modified models. In our work, we utilized existing Brendel and Drude models to extract the optical constants from spectrophotometric data of fabricated undoped and niobium doped titanium oxide thin films. The individual contributions by the two models were studied to establish influence on the dielectric function. The effect of dopants on their influences was also analyzed. Results indicate a minimal contribution from the Drude term due to the dielectric nature of the undoped films. However as doping levels increase, the rise in the concentration of free electrons favors the use of Drude model

Evaluation of the Technical Wind Energy Potential of Kisii Region Based on the Weibull and Rayleigh Distribution Models

Background. Global warming is a growing threat in the world today mainly due to the emission of CO2 caused by the burning of fossil fuel. Consequently, countries are being forced to seek potential alternative sources of energy such as wind, solar, and photovoltaic among many others. However, the realization of their benefits is faced with challenges. Though wind stands a chance to solve this problem, the lack of adequate site profiles, long-term behavioural information, and specific data information that enables informed choice on site selection, turbine selection, and expected power output has remained a challenge to its exploitation. In this research, Weibull and Rayleigh models are adopted. Wind speeds were analyzed and characterized in the short term and then simulated for a long-term measured hourly series data of daily wind speeds at a height of 10 m. The analysis included daily wind data which was grouped into discrete data and then calculated to represent the mean wind speed, diurnal variations, daily variations, and monthly variations. To verify the models, statistical tools of Chi square, RMSE, MBE, and correlational coefficient were applied. Also, the method of measure, correlate, and predict was adopted to check for the reliability of the data used. The wind speed frequency distribution at the height of 10 m was found to be 2.9 ms-1 with a standard deviation of 1.5. From the six months’ experiments, averages of wind speeds at hub heights of 10 m were calculated and found to be 1.7 m/s, 2.4 m/s, and 1.3 m/s, for Ikobe, Kisii University, and Nyamecheo stations, respectively. The wind power density of the region was found to be 29 W/m2. By a narrow margin, Rayleigh proves to be a better method over Weibull in predicting wind power density in the region. Wind speeds at the site are noted to be decreasing over the years. The region is shown as marginal on extrapolation to 30 m for wind energy generation hence adequate for nongrid connected electrical and mechanical applications. The strong correlation between the site wind profiles proves data reliability. The gradual decrease of wind power over the years calls for attention

Optical Properties of Sputter Deposited Transparent and Conducting TiO2:Nb Films

Transparent and conducting thin films of TiO2:Nb were prepared on glass by reactive dc magnetron sputtering in Ar + O-2. Post-deposition annealing in vacuum at 450 degrees C led to good electrical conductivity and optical transparency. The optical properties in the sub-bandgap region were in good agreement with Drude free electron theory, which accounts for intraband absorption. The band gap of the films was found to be in the range of 3.3 to 3.5 eV and signifies the onset of interband absorption. Electrical conductivities in the 10(-3) Omega cm range were obtained both from dc electrical measurements and from analysis of the optical measurements

Spectrally selective reflector surfaces for heat reduction in concentrator solar cells : modeling and applications of TiO(2):Nb-based thin films

The energy conversion efficiency of a conventional pn junction solar cell decreases as the temperature increases, and this may eventually lead to failures in the photovoltaic system, especially if it uses concentrated solar radiation. In this work, we show that spectrally selective reflector (SSR) surfaces can be important for reducing the heat buildup on passively cooled solar cells. We outline a computational scheme for optimizing DC magnetron-sputtered TiO(2):Nb-based SSRs tailored for silicon solar cells and find good agreement of the reflectance with an experimental realization of the optimal SSR. A figure of merit for SSRs has also been derived and applied to the experimental data