Catechol, common in industrial wastewater, is very toxic and non-biodegradable, and its desirable removal is still a challenge. Catalytic ozonation as an effective advanced oxidation process, however was limited by the application of intricately fabricated catalysts. Herein, catalytic ozonation by OH (generated by common sodium hydroxide) with the aid of calcium was developed for catechol degradation and mineralization in this study. The removal performance, mechanism and products were investigated. The results showed that ozonation at pH 12.5 could achieve complete catechol removal and excellent mineralization (maximum of 75 % COD removal efficiency) within 15 min. The adorable effect of calcium for enhanced organics removal was observed at pH 12.5, with the formation of precipitates as well. Catechol and COD removal were fitted to the pseudo-first-order kinetic model, while the reaction constant was increased by higher pH and calcium concentration. The results of quenching experiment and EPR affirmed •OH and •O radicals were pivotal for the enhanced organics removal. In addition, DFT calculation revealed the O atoms were reactive sites for electrophilic and radical attack via molecular electrostatic potential, highest occupied molecular orbital, lowest unoccupied molecular orbital and Fukui index. UPLC-Q-TOF-MS analysis revealed the intermediate products and verified the brilliant performance of catalytic ozonation. According to reactive sites and intermediates identification, the degradation pathway of catechol was proposed. As tawny precipitate appeared after reaction, the characteristics of insoluble product was analyzed using FTIR, XRD and XPS. The component of the precipitate was recognized as calcium oxalate and calcium carbonate, accompanied by the decreased Ca concentration at high pH, which declared the enhanced removal was linked to the precipitation of Ca. Finally, toxicity assessment stated the lower acute toxicity, bioconcentration factor, developmental toxicity and mutagenicity of intermediates, indicating that calcium-aid ozonation catalyzed by high pH was useful for both catechol degradation and toxicity reduction. This study provides a reference for understanding the performance and mechanism of catechol degradation. More importantly, as an environmentally friendly process, catalytic ozonation possesses a great application potential for treatment of wastewater containing metal ions in terms of simultaneous removal of organics and metal ions.

中文翻译：

---

pH值对钙助臭氧氧化中儿茶酚降解和矿化的影响：性能、机理和产物分析

儿茶酚常见于工业废水中，毒性很大且不可生物降解，其去除仍然是一个挑战。催化臭氧化作为一种​​有效的高级氧化工艺，然而受到复杂制造的催化剂的应用的限制。在此研究中，通过 OH（由普通氢氧化钠产生）在钙的帮助下进行催化臭氧化，用于儿茶酚的降解和矿化。研究了其去除性能、机理和产物。结果表明，pH 12.5 的臭氧氧化可在 15 分钟内实现儿茶酚的完全去除和良好的矿化（COD 去除效率最大为 75%）。在 pH 12.5 时观察到钙对于增强有机物去除的可爱作用，同时也形成沉淀。儿茶酚和 COD 去除符合准一级动力学模型，而反应常数随着较高的 pH 值和钙浓度而增加。淬灭实验和EPR的结果证实·OH和·O自由基对于增强有机物去除至关重要。此外，DFT计算表明O原子是通过分子静电势、最高占据分子轨道、最低未占据分子轨道和福井指数进行亲电和自由基攻击的反应位点。 UPLC-Q-TOF-MS 分析揭示了中间产物并验证了催化臭氧氧化的出色性能。根据反应位点和中间体的鉴定，提出了儿茶酚的降解途径。由于反应后出现黄褐色沉淀，利用FTIR、XRD和XPS对不溶产物的特性进行了分析。沉淀物的成分被认为是草酸钙和碳酸钙，伴随着高pH值下Ca浓度的降低，这表明去除的增强与Ca的沉淀有关。最后，毒性评估表明中间体具有较低的急性毒性、生物浓缩因子、发育毒性和致突变性，表明高pH催化的钙辅助臭氧化对于儿茶酚降解和毒性降低都是有用的。该研究为了解儿茶酚降解性能和机制提供参考。更重要的是，催化臭氧化作为一种​​环境友好的工艺，在同时去除有机物和金属离子方面，在处理含金属离子废水方面具有巨大的应用潜力。