Abstract
Zinc oxide (ZnO) photocatalysts were synthesized by sol–gel method using zinc acetate as precursor for degradation of azo dyes under UV irradiation. The resultant samples were characterized by different techniques, such as XRD, SEM, and EDX. The influence of preparation conditions such as calcination temperature and composite ratio on the degradation of methyl orange (MO) was investigated. ZnO prepared with a composite ratio of 4:1 and calcination temperature of 400 °C exhibited 99.70% removal rate for MO. The effect of operation parameters on the degradation was also studied. Results showed that the removal rate of azo dyes increased with the increased dosage of catalyst and decreased initial concentration of azo dyes and the acidic condition is favorable for degradation. Furthermore, the kinetics and scavengers of the reactive species during the degradation were also investigated. It was found that the degradation of azo dyes fitted the first-order kinetics and superoxide ions were the main species. The proposed photocatalyst can efficiently and rapidly degrade azo dyes; thus, this economical and environment-friendly photocatalyst can be applied to the treatment of wastewater contaminated with synthetic dyes.
Highlights
Synthetic organic dyes are used in the textile, paper, plastic leather, food, and other industries
Effect of Preparation Conditions of Zinc oxide (ZnO) on methyl orange (MO) Degradation Calcination Temperature Figure 1 shows the comparison of the activities of the photocatalysts prepared at different calcination temperatures (300, 400, 500, 600 °C)
The degradation efficiency of the ZnO samples for MO followed the order 400 °C > 500 °C > 600 °C > 300 °C after UV irradiation for 30 min, which may be related to the particle size of the photocatalyst
Summary
Synthetic organic dyes are used in the textile, paper, plastic leather, food, and other industries. Photocatalysis can be conveniently applied for their degradation of dye pollutants because it can mineralize organic dyes completely into H2O, CO2, and mineral acids without bringing secondary pollution. Metal semiconductor materials, such as TiO2 [8], ZnO [9], Fe2O3 [10], CdS [11], and ZnS [12], are used as photocatalyst. It is reported that among various semiconductors, zinc oxide (ZnO) exhibits higher efficiency in the photocatalytic degradation of some organic dyes than TiO2 [13, 14]. The current study provides a basis for the application of ZnO as a photocatalyst to alleviate azo dye pollution
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