Nd-ZnO Catalysts for Photocatalytic Degradation of Metronidazole

Conventional water treatment processes are unable to effectively degrade metronidazole (MNZ), leading to its accumulation in wastewater and posing a serious threat to aquatic environments and human health. Photocatalysis offers an environmentally friendly and stable method for removing organic pollutants. However, zinc oxide (ZnO) has a large bandgap, limiting its light absorption to the ultraviolet region. To overcome this limitation, this study synthesized a series of Nd-ZnO catalysts with different neodymium molar ratios (0.2%, 0.5%, 0.7%, and 1.0%) via a one-step hydrothermal method. UV–vis spectroscopy confirmed that the bandgap decreased from 3.22 to 3.18 eV after Nd doping, while the photocurrent response was enhanced and the e − –h + recombination rate was reduced. When the catalyst dosage was 10 mg and the initial MNZ concentration was 10 mg·L −1 , the degradation efficiency of 0.5 mol% Nd-ZnO reached 94.3% after 180 min of irradiation with a 400 W metal halide lamp. First-order reaction kinetics fitting yielded a reaction rate constant of 0.013 min −1 , which is 1.7 times that of pure ZnO; after five cycles, the degradation efficiency remained as high as 87.7%. It provides an effective photocatalyst for the treatment of antibiotic wastewater and offers important insights into the performance of rare-earth-modified ZnO. Graphical Nd-ZnO catalyst was synthesized via a one-step hydrothermal method. The incorporation of Nd introduces an unfilled 4f electronic structure, which can capture electrons, thereby suppressing the recombination of e − /h + pairs and effectively inhibiting photogenerated electron–hole recombination, thus enhancing the photocatalytic efficiency. The 0.5 mol% Nd-ZnO achieved a degradation efficiency of 94.3% for metronidazole within 180 min and retained 87.7% activity after five cycles.