Cobalt Single-Atom-Bonded Covalent Heptazine Framework Selectively Generates Nonradicals in Fenton-Like Catalysis for Rapidly Purifying Organic Wastewater

Abstract

Engineering the coordination architecture of cobalt single-atom catalysts (Co-SACs) represents a promising strategy to activate peroxymonosulfate (PMS) for sewage purification. In this study, Co single atoms were bonded to a 2,2′-bipyridine-bridged covalent heptazine framework (Bpy-CHF). The obtained Bpy-CHF-Co_0.6 catalyst contained highly homogeneous Co-N active sites and succeeded in achieving efficient generation of ¹O₂. Density functional theory (DFT) calculations showed that the Co sites tended to adsorb the terminal oxygen of PMS, which facilitated the oxidation of PMS to generate SO₅^•− and achieved efficient generation of ¹O₂, accompanied by the formation of Co(IV)=O. Furthermore, the catalyst demonstrated durability against a variety of environmental conditions, indicating potential for practical applications, and we fixed it on a PVDF microfiltration membrane to establish a continuous flow system. This study proposes innovative concepts for the advancement of catalysts that facilitate efficient and selective degradation of pollutants, as well as new insights into the selective generation of ¹O₂ and the formation of Co(IV)=O.

Keywords

Co-SACs / covalent heptazine framework / non-radical / peroxymonosulfate

References

[1] P. Wang, Z. Zhao, L. Zhang, S. Zhan, and Y. Li, “Revealing the Role of Binary Distortion in PMS Activation Over Spinel Toward Efficient New Pollutants Removal,” Advanced Functional Materials34, no. 25 (2024): 2316542.

[2] Y. Lu, C. Ding, J. Guo, et al., “Cobalt-Doped ZnAl-LDH Nanosheet Arrays as Recyclable Piezo-Catalysts for Effective Activation of Peroxymonosulfate to Degrade Norfloxacin: Non-radical Pathways and Theoretical Calculation Studies,” Nano Energy112 (2023): 108515.

[3] J. Zhen, J. Sun, X. Xu, et al., “M−N₃ Configuration on Boron Nitride Boosts Singlet Oxygen Generation via Peroxymonosulfate Activation for Selective Oxidation,” Angewandte Chemie International Edition63, no. 26 (2024): e202402669.

[4] Z. Weng, Y. Lin, S. Guo, et al., “Site Engineering of Covalent Organic Frameworks for Regulating Peroxymonosulfate Activation to Generate Singlet Oxygen With 100% Selectivity,” Angewandte Chemie International Edition135, no. 43 (2023): e202310934.

[5] Y. Huang, K. Zhu, Z. Hu, et al., “Rongliang Qiu, Kai Yan, Solvent-Free Synthesis of Foam Board-Like CoSe₂ Alloy to Selectively Generate Singlet Oxygen via Peroxymonosulfate Activation for Sulfadiazine Degradation,” Journal of Hazardous Materials466 (2024): 133611.

[6] J. Ji, Q. Yan, P. Yin, S. Mine, M. Matsuoka, and M. Xing, “Defects on CoS_2−x: Tuning Redox Reactions for Sustainable Degradation of Organic Pollutants,” Angewandte Chemie International Edition60, no. 6 (2021): 2903-2908.

[7] N. Song, S. Ren, Y. Zhang, C. Wang, and X. Lu, “Confinement of Prussian Blue Analogs Boxes Inside Conducting Polymer Nanotubes Enables Significantly Enhanced Catalytic Performance for Water Treatment,” Advanced Functional Materials32, no. 34 (2022): 2204751.

[8] Y. He, H. Qin, Z. Wang, et al., “Fe-Mn Oxycarbide Anchored on N-Doped Carbon for Enhanced Fenton-Like Catalysis: Importance of High-Valent Metal-Oxo Species and Singlet Oxygen,” Applied Catalysis B340 (2024): 123204.

[9] L. Zhang, J. Qi, W. Chen, et al., “Constructing Hollow Multishelled Microreactors With a Nanoconfined Microenvironment for Ofloxacin Degradation Through Peroxymonosulfate Activation: Evolution of High-Valence Cobalt-Oxo Species,” Environmental Science and Technology57, no. 42 (2023): 16141-16151.

[10] Y. Meng, Y. Liu, C. Wang, et al., “Nanoconfinement Steers Nonradical Pathway Transition in Single Atom Fenton-Like Catalysis for Improving Oxidant Utilization,” Nature Communications15, no. 1 (2024): 5314.

[11] J. Miao, J. Song, J. Lang, et al., “Single-Atom MnN₅ Catalytic Sites Enable Efficient Peroxymonosulfate Activation by Forming Highly Reactive Mn(IV)–Oxo Species,” Environmental Science and Technology571, no. 10 (2023): 4266-4275.

[12] Z. Wang, E. Almatrafi, H. Wang, et al., “Cobalt Single Atoms Anchored on Oxygen-Doped Tubular Carbon Nitride for Efficient Peroxymonosulfate Activation: Simultaneous Coordination Structure and Morphology Modulation,” Angewandte Chemie International Edition61, no. 29 (2022): e202202338.

[13] X. Zhao, X. Li, Z. Zhu, et al., “Single-Atom Co Embedded in BCN Matrix to Achieve 100% Conversion of Peroxymonosulfate Into Singlet Oxygen,” Applied Catalysis B300 (2022): 120759.

[14] X. Mi, H. Zhong, H. Zhang, et al., “Crittenden, Facilitating Redox Cycles of Copper Species by Pollutants in Peroxymonosulfate Activation,” Environmental Science and Technology56, no. 4 (2022): 2637-2646.

[15] H. Zhang, Z. Lin, P. Kidkhunthod, and J. Guo, “Stable Immobilization of Nickel Ions on Covalent Organic Frameworks for Panchromatic Photocatalytic Hydrogen Evolution,” Angewandte Chemie International Edition62, no. 21 (2023): e202217527.

[16] H. Cheng, H. Lv, J. Cheng, L. Wang, X. Wu, and H. Xu, “Stable Immobilization of Nickel Ions on Covalent Organic Frameworks for Panchromatic Photocatalytic Hydrogen Evolution,” Advanced Materials34, no. 7 (2022): 2107480.

[17] X. Wang, C. Wang, H. Tan, et al., “Design of Porous Organic Polymer Photocatalysts Based on Heptazine for Efficient Photocatalytic Aerobic Oxidation,” Chemical Engineering Journal431 (2022): 134051.

[18] X. Wu, R. Zhong, X. Lv, et al., “Modulating g-C₃N₄-Based van der Waals Heterostructures With Spatially Separated Reductive Centers for Tandem Photocatalytic CO₂ Methanation,” Applied Catalysis B330 (2023): 122666.

[19] Y. Xiong, W. Sun, Y. Han, et al., “Cobalt Single Atom Site Catalysts With Ultrahigh Metal Loading for Enhanced Aerobic Oxidation of Ethylbenzene,” Nano Research14, no. 7 (2021): 2418-2423.

[20] Y. Zhao, L. Zhu, J. Tang, et al., “Switchable and Tunable Radiative Cooling: Mechanisms, Applications, and Perspectives,” ACS Nano18, no. 1 (2024): 373-382.

[21] P. Yu, X. Zhang, T. Zhang, et al., “Nitrogen-Mediated Promotion of Cobalt-Based Oxygen Evolution Catalyst for Practical Anion-Exchange Membrane Electrolysis,” Journal of the American Chemical Society146, no. 29 (2024): 20379-20390.

[22] W. Wang, Q. Song, Q. Luo, et al., “Photothermal-enabled Single-Atom Catalysts for High-Efficiency Hydrogen Peroxide Photosynthesis From Natural Seawater,” Nature Communications14, no. 1 (2023): 2493.

[23] P. Kumar, K. Kannimuthu, A. Zeraati, et al., “High-Density Cobalt Single-Atom Catalysts for Enhanced Oxygen Evolution Reaction,” Journal of the American Chemical Society145, no. 14 (2023): 8052-8063.

[24] H. Chen, Y. Xiong, J. Li, et al., “Epitaxially Grown Silicon-Based Single-Atom Catalyst for Visible-Light-Driven Syngas Production,” Nature Communications14, no. 1 (2023): 1719.

[25] S. Liu, H. Fu, F. Wang, et al., “Insight Into the Extremely Different Catalytic Behaviors of Asymmetric and Symmetric Oxygen Vacancies for Peroxymonosulfate Activation,” Applied Catalysis B346 (2024): 123753.

[26] Z. Zhao, P. Wang, C. Song, T. Zhang, S. Zhan, and Y. Li, “Enhanced Interfacial Electron Transfer By Asymmetric Cu-O_v-In Sites on In₂O₃ for Efficient Peroxymonosulfate Activation,” Angewandte Chemie International Edition62, no. 11 (2023): e202216403.

[27] Y. Zhen, S. Zhu, Z. Sun, et al., “Identifying the Persistent Free Radicals (PFRs) Formed as Crucial Metastable Intermediates During Peroxymonosulfate (PMS) Activation by N-Doped Carbonaceous Materials,” Environmental Science and Technology55, no. 13 (2021): 9293-9304.

[28] J. Song, N. Hou, X. Liu, G. Bi, Y. Wang, and Y. Mu, “Directional Formation of Reactive Oxygen Species Via a Non-Redox Catalysis Strategy That Bypasses Electron Transfer Process,” Advanced Materials36, no. 30 (2024): 2405832.

[29] L. Wu, Z. Sun, Y. Zhen, et al., “Oxygen Vacancy-Induced Nonradical Degradation of Organics: Critical Trigger of Oxygen (O₂) in the Fe–Co LDH/Peroxymonosulfate System,” Environmental Science and Technology55, no. 22 (2021): 15400-15411.

[30] H. Gong, L. Xu, C. Li, M. Pan, and M. Zhou, “Axially Coordinated Dual-Atomic-Site Catalysts for Nearly 100% Peroxymonosulfate Conversion to ¹O₂ in Membrane Filtration,” Applied Catalysis B355 (2024): 124202.

[31] L. Zhang, X. Jiang, Z. Zhong, et al., “Carbon Nitride Supported High-Loading Fe Single-Atom Catalyst for Activation of Peroxymonosulfate to Generate ¹O₂ With 100% Selectivity,” Angewandte Chemie International Edition60, no. 40 (2021): 21751-21755.

[32] L. Liang, J. Cao, Y. Zhang, et al., “Selective Adsorption of High Ionization Potential Value Organic Pollutants in Wastewater,” PNAS121, no. 29 (2024): e2403766121.

[33] Y. Pan, J. Cao, M. Xing, and Y. Zhang, “Current Mechanism of Peroxymonosulfate Activation by CobaltBased Heterogeneous Catalysts in Degrading Organic Compounds,” Environmental Science and Technology4, no. 1 (2024): 19-46.

[34] F. Mo, C. Song, Q. Zhou, and J. Wang, “The Optimized Fenton-Like Activity of Fe Single-Atom Sites by Fe Atomic Clusters–Mediated Electronic Conffguration Modulation,” PNAS120 (2024): e2300281120.

[35] Y. Deng, S. Wang, T. Zhou, et al., “Highly-Separated Co Anchored on S, O-Doped Carbon Nitride for Enhanced Peroxymonosulfate Activation: Insights Into Radical and Non-radical Pathways,” Chemical Engineering Journal497 (2024): 154580.

[36] Z. Zhu, X. Xing, Q. Qi, et al., “Fabrication of Graphene Modified CeO₂/g-C₃n₄ Heterostructures for Photocatalytic Degradation of Organic Pollutants,” Chinese Journal of Structural Chemistry42, no. 12 (2023): 100194.

[37] Z. Zhu, J. Ye, X. Tang, et al., “Vacancy-Rich CoS_x@LDH@Co-NC Catalytic Membrane for Antibiotic Degradation With Mechanistic Insights,” Environmental Science and Technology57, no. 42 (2023): 16131-16140.

[38] T. Li, X. Wang, Z. Fan, et al., “Unique Role of Doped Mo into Fe-Based Catalyst to Intensify Peroxydisulfate Activation for Micropollutants Degradation: Promote the Conversion of SO₄•- to Fe^IV = O,” Chemical Engineering Journal500 (2024): 157255.

[39] J. Pan, X. Wang, X. Yang, et al., “Insights Into the Enhanced Oxidation of Organic Micropollutants by Single-Atom Cu Catalyst Activated Peroxydisulfate: Valence-Dominated Nonradical Pathway,” Applied Catalysis B351 (2024): 123997.

[40] X. Wang, T. Li, Z. Fan, et al., “Redox Potentials of Sulfonamide Antibiotics Mediating the Electron Transfer Process in Single-Tom Cu Catalyst/Peroxymonosulfate System: Selective Removal Mechanisms for Sulfonamides,” Journal of Hazardous Materials485 (2025): 136880.

[41] T. Khiem, N. Huy, E. Kwon, et al., “Electron Transfer-Mediated Enhancement of Superoxide Radical Generation in Fenton-Like Process: Key Role of Oxygen Vacancy-Regulated Local Electron Density of Cobalt Sites,” Applied Catalysis B343 (2024): 123490.

[42] M. Chen, J. Jiang, W. Guan, et al., “Sustainable and Rapid Water Purification at the Confined Hydrogel Interface,” Advanced Materials36, no. 18 (2024): 2311416.

[43] S. Hu, W. Yan, Yu J. Yan, et al., “Degradation of Sulfamethoxazole in Water by Dielectric Barrier Discharge Plasma Jet: Influencing Parameters, Degradation Pathway, Toxicity Evaluation,” Plasma Science and Technology25, no. 3 (2023): 035510.

[44] C. Xiao, Y. Hu, Q. Li, et al., “Degradation of Sulfamethoxazole by Super-hydrophilic MoS₂ Sponge Co-catalytic Fenton: Enhancing Fe²⁺/Fe³⁺ Cycle and Mass Transfer,” Journal of Hazardous Materials458 (2023): 131878.

[45] S. Wang, J. Hu, and J. Wang, “Degradation of Sulfamethoxazole Using PMS Activated by Cobalt Sulfides Encapsulated in Nitrogen and Sulfur Co-Doped Graphene,” Science of the Total Environment827 (2023): 154379.

[46] J. Zheng, Q. Lin, Y. Liu, et al., “Peroxymonosulfate Activation by Mg-Introduced Fe-N Carbon Nanotubes to Accelerate Sulfamethoxazole Degradation: Singlet Oxygen-Dominated Nonradical Pathway,” Chemical Engineering Journal452 (2023): 139233.

[47] T. Khiem, N. Huy, E. A. KwonEbrahimi, et al., “Hetero-Interface-Engineered Sulfur Vacancy and Oxygen Doping in Hollow Co₉S₈/Fe₇S₈ Nanospheres Towards Monopersulfate Activation for Boosting Intrinsic Electron Transfer in Paracetamol Degradation,” Applied Catalysis B330 (2023): 122550.

[48] T. Sun, Y. Deng, G. Wang, et al., “Charge Carrier Controlled Free Radical Construction Efficient Photocatalytic Self-Fenton System,” Chemical Engineering Journal496 (2024): 154351.

RIGHTS & PERMISSIONS

2025 The Author(s). EcoEnergy published by John Wiley & Sons Australia, Ltd on behalf of China Chemical Safety Association.