Abstract
Nanostructured Ag-ZnO materials were successfully synthesized by first producing a ZnO with flower-like morphology using a simple precipitation method, and then Ag nanoparticles were prepared directly on the surface by a facile photoreduction method. The materials were characterized by scanning and transmission electron microscopy (SEM and TEM), by X-ray diffractometry (XRD) and atomic absorption spectrometry (AAS). They were shown to be composed of metallic Ag particles dispersed on the surface of flower-like ZnO structures. Photocatalytic effect of Ag-ZnO on the photodegradation of methyl orange (MO) under UV irradiation was investigated in aqueous suspension. The effect of pH, Ag content, photodeposition time, concentration of the organic dye and presence of Mg2+, Ca2+, NO3-, Cl- and SO42- on the photocatalytic degradation and decolorization reaction of MO was studied. The photocatalytic method was applied for the degradation of MO in several synthetic wastewater samples with satisfactory results.
Highlights
Wastewaters resulting from human activities can contain many organic and inorganic substances and are one of the main sources of environmental pollution due to the rapid development of industries
AgNO3 (0.30-1.2 mmol) was added, the suspension diluted to about 100 mL, stirred at 500 rpm in the dark for 15 min to achieve desorption/adsorption equilibrium of silver ions at room temperature, and purged with pure N2 gas for 5 min
The results obtained for the degradation/decolorization of 100 mL of methyl orange (MO) (10.0 mg L-1) in the presence of 200 mg L-1 Ag-ZnO (Figure 8) at room temperature show that for the same AgNO3 deposition solution, the photocatalyst activity increased with the photodeposition time up to 40 min and declines, as expected for the lower light absorption and increased electron-hole recombination centers as a function of the relative amount of loaded Ag (Table 1)
Summary
Wastewaters resulting from human activities can contain many organic and inorganic substances and are one of the main sources of environmental pollution due to the rapid development of industries. The ZnO precipitate was collected by centrifugation, washed with deionized water and ethanol several times, dried at 80 oC for 4 h, and used for subsequent preparation of the flower-like Ag-ZnO materials. 0.20 g of flower-like ZnO was transferred into a 250 mL beaker, dispersed in 30 mL of water and irradiated with a 400 W high-pressure mercury lamp, placed 12 cm above the solution surface for 10 min, to remove the impurities present on the surface. AgNO3 (0.30-1.2 mmol) was added, the suspension diluted to about 100 mL, stirred at 500 rpm in the dark for 15 min to achieve desorption/adsorption equilibrium of silver ions at room temperature, and purged with pure N2 gas for 5 min It was irradiated with a 400 W UV lamp for 40 min, while purging with nitrogen. At fixed intervals of time, 2 mL of sample were withdrawn, centrifuged, and the supernatant transferred into a spectrophotometer cell for measurement of the absorbance of MO at 464 and 272 nm
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