Abstract
Environmental pollution from human and industrial activities has received much attention as it adversely affects human health and bio-diversity. In this work we report efficient visible light photocatalytic degradation of phenol using supported zinc oxide (ZnO) nanorods and explore the role of surface defects in ZnO on the visible light photocatalytic activity. ZnO nanorods were synthesized on glass substrates using a microwave-assisted hydrothermal process, while the surface defect states were controlled by annealing the nanorods at various temperatures and were characterized by photoluminescence and X-ray photoelectron spectroscopy. High performance liquid chromatography (HPLC) was used for the evaluation of phenol photocatalytic degradation. ZnO nanorods with high surface defects exhibited maximum visible light photocatalytic activity, showing 50% degradation of 10 ppm phenol aqueous solution within 2.5 h, with a degradation rate almost four times higher than that of nanorods with lower surface defects. The mineralization process of phenol during degradation was also investigated, and it showed the evolution of different photocatalytic byproducts, such as benzoquinone, catechol, resorcinol and carboxylic acids, at different stages. The results from this study suggest that the presence of surface defects in ZnO nanorods is crucial for its efficient visible light photocatalytic activity, which is otherwise only active in the ultraviolet region.
Highlights
Phenol and its derivatives are widely used in several manufacturing industries and can find their way into the environment, polluting the ground water or surface water resources [1]
We study the defect-induced photocatalytic activity of zinc oxide (ZnO) nanorods with a careful comparison of the surface defect states of the ZnO nanorods using phenol as a test contaminant
Zinc oxide nanorods were synthesized on glass substrates using a microwave-assisted hydrothermal process and the surface defects in the nanorods were modulated by annealing the nanorods in air at different temperatures
Summary
Phenol and its derivatives are widely used in several manufacturing industries and can find their way into the environment, polluting the ground water or surface water resources [1]. Phenolic compounds have been found in different sewage sludge, influent and effluent of wastewater, river water and soil [4,5,6,7]. The compounds 2-nitrophenol, 4-nitrophenol and 2.4-dinitrophenol, ranging from 0.1 to 5.0 μg/L, have been reported to be present in the Ebro river in Spain [7], while up to 40 mg/L in river water was reported due to the dispersal of wastewater from the petrol industry [8]. Physicochemical methods including adsorption using activated carbon, biological treatments and advanced oxidation processes (AOPs) are generally used for the degradation of phenolic compounds in water. In the quest for purifying polluted water, photocatalysis has become
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