Enhanced ozonation of pollutants by MgO nanoclusters/sewage sludge-derived hierarchical porous carbon: experimental and theoretical study,Environmental Science: Nano

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Enhanced ozonation of pollutants by MgO nanoclusters/sewage sludge-derived hierarchical porous carbon: experimental and theoretical study
Environmental Science: Nano ( IF 5.8 ) Pub Date : 2021-06-30 , DOI: 10.1039/d1en00481f
Siyang Li _{1,

2} , Shujuan Zhan ₁ , Jingxiang Sun ₁ , Lingai Yao _{1,

2} , Jinzhu Zhu ₁ , Jinxi Feng ₁ , Ya Xiong _{1,

3} , Shuanghong Tian _{1,

3}

Affiliation

Highly reactive nanoclusters of metal oxides are extremely difficult to synthesize due to their thermodynamic instability. For the first time, MgO nanoclusters supported on sewage sludge-derived hierarchical porous carbon (MgO nanoclusters/SC) were successfully prepared by grafting 1.31 ± 0.03 mmol g⁻¹ acidic groups on the SC, then dynamically controlling the chemisorption of Mg²⁺ on the modified SC within 20 s, and finally transforming the fixed Mg²⁺ into MgO nanoclusters with a size of less than 2.4 nm via thermal treatment. Moreover, the cluster size could be facilely tailored by controlling the dynamic adsorption time and initial aqueous Mg²⁺ concentration. The resulting five MgO nanoclusters/SC-20 s samples with 0.43–1.12% (mass percentage) Mg have a turnover frequency of 0.038 towards the catalytic ozonation of 4-chlorophenol, much higher than those of the bigger nanoclusters and nanocrystals (i.e. MgO/SC-20 s with 1.43% Mg, MgO/SC-3 min with 0.85–2.0% Mg). The pseudo-first-order reaction constant of MgO nanoclusters/SC with 1.12% Mg is 0.0126 min⁻¹, 6.0 and 4.1 times that of SC and bulky MgO/SC, respectively. The presence of MgO nanoclusters/SC also enhanced the removal of cephalexin, florfenicol and sulfamethoxazole by 54.3%, 45.5%, and 57.4%, respectively. The high activity can be ascribed to the rich and highly under-coordinated Mg in the smaller MgO nanoclusters and the unblocked hierarchical pores of the SC support. Finally, DFT calculations revealed at the atomic level that the under-coordinated Mg in MgO nanoclusters could directly or indirectly activate ozone through the protonated hydroxyl or just hydroxyl bonded to the under-coordinated Mg. Except for (MgO)₂, the smaller the nanocluster, the higher the activity. This work shed a light on the design and preparation of highly reactive nanoclusters of metal oxide catalysts for catalytic ozonation of refractory organic pollutants.

中文翻译：

氧化镁纳米团簇/污水污泥衍生的分级多孔碳增强污染物臭氧化：实验和理论研究

由于其热力学不稳定性，金属氧化物的高反应性纳米团簇极难合成。通过在SC上接枝1.31±0.03 mmol g ^-1酸性基团，然后动态控制Mg ²⁺的化学吸附，首次成功制备了负载在污水污泥衍生的分级多孔碳上的MgO纳米团簇（MgO纳米团簇/SC）。在 20 秒内将修饰的 SC，最终通过热处理将固定的 Mg ²⁺转化为尺寸小于 2.4 nm 的 MgO 纳米团簇。此外，可以通过控制动态吸附时间和初始含水 Mg ²⁺轻松调整簇大小专注。由此产生的五个 MgO 纳米团簇/SC-20 s 样品具有 0.43-1.12%（质量百分比）Mg 对 4-氯苯酚的催化臭氧化的周转频率为 0.038，远高于更大的纳米团簇和纳米晶体（即MgO/ SC-20 秒，含 1.43% Mg，MgO/SC-3 分钟，含 0.85–2.0% Mg）。MgO 纳米团簇/SC 与 1.12% Mg 的准一级反应常数为 0.0126 min ^-1，分别是 SC 和大块 MgO/SC 的 6.0 倍和 4.1 倍。MgO 纳米团簇/SC 的存在也将头孢氨苄、氟苯尼考和磺胺甲恶唑的去除率分别提高了 54.3%、45.5% 和 57.4%。高活性可归因于较小的 MgO 纳米团簇中富含且高度配位不足的 Mg 以及 SC 载体的未阻塞分级孔。最后，DFT 计算在原子水平上显示，MgO 纳米团簇中配位不足的 Mg 可以通过质子化的羟基或仅与配位不足的 Mg 键合的羟基直接或间接激活臭氧。(MgO) ₂除外，纳米团簇越小，活性越高。这项工作阐明了用于催化臭氧化难降解有机污染物的金属氧化物催化剂的高反应性纳米团簇的设计和制备。

更新日期：2021-07-30

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