A UV-assisted heterogeneous photo-Fenton process based on powder activated carbon (PAC)/Fe₃O₄ catalyst was investigated to degrade metronidazole (MTZ). Successful uniform synthesis of PAC/Fe₃O₄ has confirmed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy dispersive X-Ray spectroscopy mapping (EDX-mapping), vibrating sample magnetometer (VSM), and Fourier transform infrared spectroscopy (FTIR) techniques. The interaction of five independent variables in the MTZ degradation in the UV + \({P}{A}{C}/{{F}{e}}_{3}{{O}}_{4}\)+\({{H}}_{2}{{O}}_{2}\) photo-Fenton system was optimized by a three-level full-face-centered central composite design (CCD). Proposed model proved to have adequacy and validity in prediction of MTZ degradation (P value < 0.0001 and R² = 0.9512). Although the desirable pH for MTZ degradation was 3, Fenton-like reaction was ongoing over a wide range of pH. However, at alkaline pH, the process efficiency was more affected by MTZ concentration than acidic pH. MTZ degradation by UV+\({P}{A}{C}/{{F}{e}}_{3}{{O}}_{4}\) + \({{H}}_{2}{{O}}_{2}\) heterogeneous Fenton system followed the pseudo-first-order model (R² > 0.95). High stability, reusability, and separation capability of PAC/Fe₃O₄ were confirmed by EDX and VSM analyses and iron leach investigation. This process could represent the MTZ degradation, DOC, and COD removal efficiencies of 96.12%, 93.67, and 94.87%, respectively. Also, increasing of the AOS value from -0.422 to 0.437 and increasing of the COS value from -0.422 to 3.773 indicate that the MTZ has been highly mineralized and the solution biodegradability has been improved. MTZ degradation intermediates, mechanism, and pathways were proposed. The abundancy of intermediates with m/z < 70 confirmed the strong degradation of MTZ in the photo-Fenton system.

Graphical abstract

中文翻译：

---

使用 PAC/Fe3O4 磁性催化剂改善多相光芬顿氧化系统中甲硝唑的降解：生物降解性、催化剂规格、工艺优化和降解途径

研究了基于粉末活性炭 (PAC)/Fe ₃ O ₄催化剂的紫外线辅助多相光芬顿工艺降解甲硝唑 (MTZ)。PAC/Fe ₃ O _{4 的}成功均匀合成已通过 X 射线衍射 (XRD)、场发射扫描电子显微镜 (FE-SEM)、能量色散 X 射线光谱映射 (EDX-mapping)、振动样品磁强计 (VSM) 证实) 和傅里叶变换红外光谱 (FTIR) 技术。UV下MTZ降解中五个自变量的相互作用 +  \({P}{A}{C}/{{F}{e}}_{3}{{O}}_{4}\) + \({{H}}_{2}{{O}}_{2}\)photo-Fenton系统通过三级全面面居中中央复合设计（CCD）进行了优化。所提出的模型证明在预测 MTZ 退化方面具有充分性和有效性（P 值 < 0.0001 和 R ²  = 0.9512）。尽管 MTZ 降解的理想 pH 值为 3，但类芬顿反应仍在很宽的 pH 范围内进行。然而，在碱性 pH 值下，工艺效率受 MTZ 浓度的影响比酸性 pH 值更大。MTZ 由 UV+ 降解\({P}{A}{C}/{{F}{e}}_{3}{{O}}_{4}\) + \({{H}}_{2 }{{O}}_{2}\)异构 Fenton 系统遵循伪一阶模型 (R ²  > 0.95)。PAC/Fe ₃ O _{4 的}高稳定性、可重复使用性和分离能力经 EDX 和 VSM 分析以及铁浸出调查证实。该过程可以代表 MTZ 降解、DOC 和 COD 去除效率分别为 96.12%、93.67 和 94.87%。此外，AOS 值从 -0.422 增加到 0.437 和 COS 值从 -0.422 增加到 3.773 表明 MTZ 已高度矿化并且溶液生物降解性得到改善。提出了MTZ降解中间体、机制和途径。大量 m/z < 70 的中间体证实了光芬顿系统中 MTZ 的强烈降解。

图形概要