Photocatalytic reduction of chromium(VI) in aqueous solution using dye-sensitized nanoscale ZnO under visible light irradiation |
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Authors: | Gordon C C Yang Sheng-Wei Chan |
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Institution: | (1) Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, 80424, Taiwan |
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Abstract: | Photocatalytic removal of Cr6+ from aqueous solution using dye-sensitized nanoscale ZnO under visible light irradiation was studied in this work. First,
nanoscale ZnO was prepared by the co-precipitation method. Then, sensitization of nanoscale ZnO by Alizarin Red S dye followed.
Further, nanoscale ZnO and dye-sensitized nanoscale ZnO (designated nanoZnO and nanoZnO*, respectively) were both characterized
by various photospectrometry methods, such as scanning electron microscopy (SEM), scanning electron microscopy-energy dispersive
X-ray spectrometry (SEM-EDS), EDS-mapping, transmission electron microscopy (TEM), and X-ray diffractometry (XRD). It was
found that both types of prepared particles are spherical in shape with a size range of 20 to 50 nm. XRD patterns showed that
both nanoZnO and nanoZnO* had the same crystalline structure of zincite. In the photocatalytic reduction aspect, effects of
different light sources and dosage of nanoZnO* on Cr6+ reduction (Cr6+]initial = 20 mg/L) were evaluated in this work. Treatment of chromium(VI)-bearing wastewater under the conditions of using 1.0 g/L
of nanoZnO*, neutral pH, irradiation of household fluorescence lamps for 6 h and 17 h would yield Cr6+ removal efficiencies of about 68% and 90%, respectively. When the household fluorescence lamps were replaced by visible-light
lamps of 400–500 nm in wavelength, the corresponding removal efficiencies dropped to about 50% and 75%, respectively. When
nanoZnO* was irradiated by sunlight under almost the same experimental conditions, the Cr6+ reduction efficiency increased up to 90%. In summary, sensitizing nanoscale ZnO with Alizarin Red S dye for photocatalytic
applications using visible light is feasible. The relevant reaction mechanism and pathways were also proposed in this work. |
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Keywords: | Photocatalysis Chromium(VI) Dye-sensitized Nanoscale ZnO Visible light irradiation Nanotechnology Occupational health EHS |
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