Abstract

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.

Highlights

  • Contaminated waste water from industries, refineries, agriculture run-off, domestic and sewage water contain organic pollutants that are harmful to human and the ecosystem in general

  • Light energy greater than that of zinc oxide (ZnO) band gap illuminated on its surface excites electrons from its valence band to the conduction band leaving behind holes in the valence band

  • A white ZnO thin film formed on Zinc electrode surface as a result of the redox reactions at the anode and cathode

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Summary

Introduction

Contaminated waste water from industries, refineries, agriculture run-off, domestic and sewage water contain organic pollutants that are harmful to human and the ecosystem in general. Photocatalysis is applied in air purification, in antibacterial action, hydrogen evolution through water splitting, designing self-cleaning surfaces, sterilization and photo electrochemical conversion In these applications, semiconductors are used as photocatalysts. ZnO possess unique properties like photosensitivity, nontoxicity, environmental stability and good optical and electrical properties These properties according to [9] have attracted much interest in varied applications. It has high electron mobility, good thermal conductivity and transparency All these properties make ZnO a promising material in several semiconductor applications including designing of transparent thin film transistors, Fabrication and Characterization of Cobalt-Pigmented Anodized Zinc for Photocatalytic. They are vital in applications like antibacterial use as reported by [10], dye sensitized solar cells by [11] gas sensors by [12] and photocatalysis as reported by [13]

ZnO photocatalytic water treatment
Fabrication of zinc oxide thin films and nanostructures
Anodization
Experiment
Data analysis
Results
Reflectance spectra
Absorption coefficient
Photocatalytic degradation of methylene blue
Conclusion
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