Abstract
In order to enhance the photodegradation of methyl orange (MO) by ZnO under visible light irradiation, ZnO nanoparticles co-doped with Ag and N and supported on activated carbon (AC) with different properties were synthesized through the sol-gel method. The prepared photocatalysts were characterized in terms of the structure and properties through X-ray diffraction, N2 adsorption-desorption, ultraviolet-visible (UV-vis), diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, photoluminescence, and electron spin resonance. The photocatalytic activities of these photocatalysts followed the order: Ag-N-ZnO/ACs > Ag-N-ZnO > N, or Ag single-doped ZnO > commercial ZnO. This result was attributed to the small particle size, large surface area, narrow band gap, and high charge separation of Ag-N-ZnO/ACs. The Ag-N-ZnO/coconut husk activated carbon (Ag-N-ZnO/CHAC) exhibited the highest degradation efficiency of 98.82% for MO under visible light irradiation. This outcome was due to the abundant pore structure of Ag-N-ZnO/CHAC, resulting in stronger adsorption than that of other Ag-N-ZnO/ACs. Moreover, the degradation of MO on photocatalysis followed first order kinetics. The reactive species ·OH and ·O2− played more important roles in the photocatalytic degradation of MO over composite photocatalyst. Ag-N-ZnO/CHAC photocatalyst exhibited higher photocatalytic activity than unsupported Ag-N-ZnO after five recycling runs.
Highlights
With the rapid development of global industry, more and more environmental problems—especially water pollution—are caused by organic pollutants
2.0 g CHAC was dispersed in 200 mL ethanol for 1 h under sonication and 0.2 g Zinc oxide (ZnO) was dispersed in 50 mL ethanol for 20 min
The Ag-N-ZnO and Ag-N-ZnO/activated carbon (AC) composites with different ACs loading have the similar X-ray diffraction (XRD) patterns, which implied that the addition of Ag, N and AC does not change the phase structure of ZnO
Summary
With the rapid development of global industry, more and more environmental problems—especially water pollution—are caused by organic pollutants. Methyl orange (MO) is the most representative of all anionic azo dyes, which is not decomposed under ambient conditions and is usually resistant to classical biological treatment Conventional physicochemical techniques, such as adsorption, coagulation, and reverse osmosis, are the most frequently developed to remove MO from aqueous solutions. Sunlight consists of approximately 5% UV, 43% visible and 52% infrared [10] light, the wide band gap of ZnO limits its photoactivity under visible light, which limits its applications that use sunlight as the energy source Another drawback of ZnO is the rapid recombination rate of the photogenerated electron-hole pair, which limits the photodegradation reaction under normal conditions [11].
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