山东大学/山东科技大学ACB: 单原子催化点位的微环境调控实现类芬顿体系自由基/电子转移过程的同步强化

图文摘要

成果简介

近日，山东科技大学尚亚男、山东大学许醒等合作在 Applied Catalysis B: Environmental 上发表了题为“ Microenvironment modulation of cobalt single-atom catalysts for boosting both radical oxidation and electron-transfer process in Fenton-like system” 的研究论文 。该文章通过对碳基钴单原子催化剂（ Co-SACs ）的钴 - 氮配位结构（ Co-N _x ）进行微环境调控，探究了微环境调控下的不同配位结构（ Co-N ₃ 和 Co-N ₄ ）活化过硫酸盐（ PMS ）的自由基 / 非自由基途径及对污染物马卡西平（ CBZ ）的降解性能。结果表明， 与 Co-N ₄ 配位结构相比， Co-N ₃ 配位结构可以更好地调节金属 - 载体的微环境活化 PMS ，产生更多的自由基并促进催化体系中的电子转移过程（ ETP ） 。这项工作从单原子配位结构的微环境角度，为解释碳基 SACs/PMS 体系的多路径活化机制提供了新思路 。

引言

基于 N 原子的高电负性以及对金属原子的强亲和力，目前大部分的碳基 SACs 主要通过 N 原子掺杂的方式构造金属单原子位点，以限制金属原子在碳基载体上的迁移和团聚，并增强金属与载体的相互作用。借助金属单原子与 N 配位原子之间的强相互作用，金属 - 氮配位结构（ M‒N _x ）能够调控金属单原子的电荷密度及电子结构，并影响其与 PMS 的结合强度和构型、电荷传递以及特定污染物降解反应的能垒。因此，设计具有不同配位结构的单原子催化剂将有助于深入了解单原子催化剂的电子结构 - 吸附 / 催化活性之间的关系，并揭示不同氧化途径的机制与作用 。

图文导读

合成方法

Fig. 1 (a) Fabricating scheme of Co-N ₃ and Co-N ₄ catalysts using chitosan as starting material; (b) HADDF-HRTEM of Co-N ₃ catalyst; (c) HRTEM mappings of Co-N ₃ ; (d) HADDF-HRTEM of Co-N ₄ ; (e) HRTEM mappings of Co-N ₄ catalyst. Copyright 2023, Elsevier Inc .

Fig. 2 (a) XANES of Co-N ₃ and Co-N ₄ catalysts at energy of 7690-7780 eV; (b) Energy at 7700-7725 eV; (c) FT-EXAFS of the two Co-SACs; (d) WT-EXAFS spectra of Co-N ₃ and Co-N ₄ catalysts; (d-e) Comparison between the experimental K-edge XANES spectra and the theoretical spectra of (d) Co-N ₄ and (e) Co-N ₃ catalysts (The gray, blue and pink balls refer to C, N, and Co atoms, respectively). (e) XPS N 1s spectra of N-C, Co-N ₄ and Co-N ₃ catalysts; (f) XRD patterns of N-C, Co-N ₄ and Co-N ₃ catalysts. Copyright 2023, Elsevier Inc .

通过定量 EXAFS 拟合分析验证了两种 Co-SACs 的精确配位结构。 EXAFS 拟合后，计算出两个 Co-SACs 中的 Co-N 配位数分别为 3.1 和 4.0 。我们还分析了 Co-N ₃ 和 Co-N ₄ 俩种模型的 XANES 拟合图谱，并将其与实验图谱进行了比较。结果表明， Co-N ₃ 和 Co-N ₄ 的理论计算图谱与实验结果具有相似的特征。例如， Co-N ₃ 实验图谱在 7732 eV 左右峰的结构与 Co-N ₃ 的理论结果非常相似 。

不同配位结构的活化机制

Fig. 3 (a) Degradationof CBZ in different catalytic systems; (b) The k _obs values of CBZ in different catalytic systems; (c) CBZ oxidation in Co-N ₄ /PMS and Co-N ₃ /PMS systems with different PMS dosages, (d) CBZ oxidation in Co-N ₄ /PMS and Co-N ₃ /PMS systems with different catalyst dosage; (e) Comparison of the k _obs of CBZ in different catalytic systems. (CBZ concentration: 10 mg/L; PMS dosage: 0.5 mM; catalyst dosage: 0.1 g/L). Copyright 2023, Elsevier Inc .

Fig. 4 (a) The k _obs values of CBZ oxidation in Co-N ₃ /PMS and Co-N ₄ /PMS systems by using differentscavengers; (b) DMPO adducts in PMS only, Co-N ₃ /PMS (0.5 mM), Co-N ₃ /PMS (2.0 mM), and Co-N ₄ /PMS (2.0 mM) systems; (c) CBZ oxidation in Co-N ₃ /PMS and Co-N ₄ /PMS systems by replacement of H ₂ O with D ₂ O; (d) The k _obs of CBZ oxidation in H ₂ O and D ₂ O solutions; (e) PMSO and PMSO ₂ concentrations at PMS of 0.5 mM in PMS alone, Co-N ₃ /PMS, and Co-N ₄ /PMS systems. (CBZ concentration: 10 mg/L; PMS dosage: 0.5 mM; catalyst dosage: 0.1 g/L) Copyright 2023, Elsevier Inc .

Fig. 5 (a) The k _obs of CBZ oxidation in Co-N ₃ /PMS and Co-N ₄ /PMS systems with premixing catalyst and PMS (CBZ concentration: 10 mg/L; PMS dosage: 0.5 mM; catalyst dosage: 0.1 g/L); (b) Open-potential in Co-N ₃ /PMS and Co-N ₄ /PMS systems; (c) A scheme of galvanic oxidation system; (d) Current generation in GOS coating with different catalysts (Co-N ₃ , Co-N ₄ , and N-C). Copyright 2023, Elsevier Inc .

降解实验表明， Co-N ₃ /PMS 体系对 CBZ 的降解速率要高于 Co-N ₄ /PMS 体系。自由基淬灭实验、原位电子顺磁光谱（ ESR ）和电化学实验（盐桥实验、开路电势）测试揭示在俩种 Co-SACs 催化体系（ Co-N ₃ /PMS 和 Co-N ₄ /PMS ）中，自由基和 ETP 在 CBZ 的降解过程中起主要作用，其余催化路径（高价钴氧化、单线态氧）的作用很小。同时， 与 Co-N ₄ 配位结构相比， Co-N ₃ 配位结构可以更好地调节金属 - 载体的微环境活化 PMS ，产生更多的自由基并促进催化体系中的 ETP 反应 。

DFT 计算

Fig. 6 (a) Energy barriers of radical pathways in Co-N ₄ /PMS and Co-N ₃ /PMS systems; (b) Gaps of LUMO of Co-N ₃ /PMS or Co-N ₄ /PMS and HOMO of CBZ. Copyright 2023, Elsevier Inc .

DFT 计算显示， Co-N ₃ 构型中的 Co 原子凸出于碳基平面，而 Co-N ₄ 的构型为纯平面结构。因此， Co-N ₃ 构型中凸出的 Co 原子与 PMS 分子的结合具有更小的空间位阻效应，表现出更大的吸附能和热力学稳定性。同时， Co-N ₃ /PMS 复合物与污染物分子之间具有较低的 HOMO-LUMO 能隙，有利于通过 ETP 促进 CBZ 的高效降解 。

性能分析

Fig. 7 (a) The degradation of CBZ in Co-N ₃ /PMS system under different pH conditions; (b) k _obs values of CBZ adsorption and degradation in Co-N ₃ /PMS system; (c) CBZ degradation by the leached Co ion in Co-N ₃ /PMS system under different pH conditions; (d) CBZ degradation in Co-N ₃ /PMS system with the background of different anions; (e) Stability test of Co-N ₃ under different PMS dosages; (f) Removal efficiency of CBZ after different cycles. (CBZ concentration: 10 mg/L; PMS dosage: 0.5 mM; catalyst dosage: 0.1 g/L). Copyright 2023, Elsevier Inc.

Fig. 8 (a) Degradation of different organics in Co-N ₃ /PMS system (organics concentration: 10 mg/L; PMS dosage: 0.5 mM; catalyst dosage: 0.1 g/L); (b) The k _obs values of different organics in Co-N ₃ /PMS system; (c) Scheme of catalytic carbon-fiber filter; (d) SEM of the Co-N ₃ coated carbon-fiber; (e) Degradation of different pollutants in the Co-N ₃ coated catalytic filter (Co-N ₃ dosage: 15 mg). Copyright 2023, Elsevier Inc.

Fig. 9  (a) Fukui values of all atoms in the CBZ molecule; (b) Possible transformation pathways of CBZ in the Co-N ₃ /PMS system. Copyright 2023, Elsevier Inc.

小结

作者介绍

备注：

Permissions for reuse of all Figures have been obtained from the original publisher. Copyright 2023, Elsevier Inc

参考文献：

K.X. Yin, R.X. Wu, Y.N. Shang, D.D. Chen a, Z. Wu, X.H. Wang, B.Y. Gao, X. Xu, Microenvironment Modulation of Cobalt Single-atom Catalysts for boosting both radical oxidation and electron-transfer process in Fenton-like system, Applied Catalysis B: Environmental, https://doi.org/10.1016/j.apcatb.2023.122558

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