Degradation of Paracetamol in Distilled and Drinking Water via Ag/ZnO Photocatalysis under UV and Natural Sunlight

The present study demonstrates the synthesis and application of Ag/ZnO powder films (thickness of 4 mu m) as photocatalysts for natural sunlight and ultraviolet (UV, 315-400 nm) irradiation. The synthesis procedure is simple and eco-friendly, based on the photo-fixation of silver ions onto commercial ZnO powder via UV illumination for the first time. The photocatalytic efficiency of the newly developed films is evaluated through degradation of paracetamol in distilled and drinking water. Our experimental evidences show that the Ag/ZnO nanostructure films are more active than pristine ZnO films in the photodegradation process. Namely, the photocatalytic efficiency of the films modified with 10(-2) M concentration of silver ions achieve the highest degradation (D) percentages for paracetamol in both types of water (D-distilled = 80.97%, D-drinking = 82.5%) under natural sunlight. Under UV exposure, the degradation percentages are slightly lower but still higher than those achieved by pure ZnO films (D-distilled = 53.13%, D-drinking = 61.87%). It is found that the photocatalytic activity grows in direct proportion to the concentration of Ag+ ions: ZnO < Ag 10(-4)/ZnO < Ag 10(-3)/ZnO < Ag 10(-2)/ZnO. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance and photoluminescence spectroscopy are used to characterize the as-prepared ZnO and Ag/ZnO nanostructures. The improved photocatalytic performance of the Ag/ZnO films is mostly attributed to the combination of excited electron transfer from ZnO to Ag and the inhibition of photogenerated electron-hole pair recombination. Furthermore, Ag/ZnO nanostructure films can retain their photocatalytic activity after three cycles of use, highlighting their potential practical application for the treatment of pharmaceutical wastewater in real-world scenarios where natural sunlight is often more readily available than artificial UV light.