Hybridizing Ag-Doped ZnO nanoparticles with graphite as potential photocatalysts for enhanced removal of metronidazole antibiotic from water

• Published in: Journal of environmental management 2019-12, Vol.252, p.109611-109611, Article 109611
• Main Authors: Tran, Mai Lien, Nguyen, Chi Hieu, Fu, Chun-Chieh, Juang, Ruey-Shin
• Format: Article
• Language: English
• Subjects: Ag doping; Degradation pathways; Graphite; Metronidazole; Photocatalysis; ZnO
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2019.109611

In this study, the ZnO nanoparticles were doped with Ag and then hybridized on graphite (GP) layer (Ag–ZnO/GP) by a hydrothermal method, which was used as photocatalysts to remove metronidazole (MNZ) antibiotic from aqueous solutions. The fine structure, morphologies, and optical properties of the synthesized composites were first examined. The incorporation of Ag would readily reduce the rate of the recombination of electron-hole pairs and enhance the photocatalytic activity in a wide range of light wavelength. The graphite surface also acted as an electron sink to efficiently inhibit the photocorrosion of ZnO, thereby improving the photostability of the composites. The composition of the composite was optimized to be 0.5 wt% GP/ZnO and 1.0 wt% Ag/ZnO according to the extent of the enhancement of photocatalytic activity. In a solution containing 30 mg L−1 of MNZ and 0.5 g L−1 of Ag–ZnO/GP composite, it was shown that 88.5% and 97.3% of MNZ was removed after 60 min of 100-W UV and 180-min solar irradiation, respectively. Moreover, six over a total of eleven transformation products formed during UV photocatalysis were ascribed to the roles of reactive holes (h+), all which were detected and identified by high-resolution liquid chromatography-mass spectrometry (LC-MS). Finally, the pathways of MNZ degradation over Ag–ZnO/GP composite were proposed. The Ag-doped ZnO nanoparticles were hybridized with graphite (called the Ag–ZnO/GP). Both Ag particles and carbon play as electron sinks to reduce the recombination of photogenerated charge carriers. In addition, the photocorrosion behavior of ZnO was inhibited due to the distribution of Ag-doped ZnO into the surface of carbon sheets, leading to the higher stability of the catalyst. Photocatalysis removal of metronidazole (MNZ) antibiotic over Ag–ZnO/GP composites could be efficiently achieved under UV and solar light. The transformation products formed during UV photocatalysis were mainly caused by the attack of oxidizing agent holes, h+. These intermediates quickly disappeared after 120 min of UV irradiation, demonstrating efficient and quick mineralization of MNZ. [Display omitted] •The Ag-doped ZnO nanoparticles hybridized with graphite (Ag–ZnO/GP) was hydrothermally synthesized.•The Ag–ZnO/GP composites displayed high photocatalytic activity under both UV and solar light.•The active agent hole h+ participated in the degradation of MNZ over Ag–ZnO/GP composites.•Eleven intermediates were involved in the pathwa