In situ observation of Co₃O_4−α–OH formation on optimized biochar for peroxymonosulfate activation and ultrafast antibiotics degradation

Abstract

Biochar optimized with oxygen-containing functional groups is believed to be beneficial for peroxymonosulfate (PMS) activation, and biochar-loaded Co₃O₄-based catalysts are expected to be one of the most promising PMS activators for the efficient removal of organic pollutants. Nevertheless, the real active sites on Co₃O₄ catalysts are still in debate due to insufficient experimental evidence. Herein, Co₃O₄ growing on the oxygen-containing functional groups optimized rice husk biochar (RHBA) was synthesized (RHBA@Co₃O₄), and RHBA800@25Co₃O₄ + PMS system achieved complete degradation (100%) of refractory levofloxacin (LFX) within 4 min. The superior catalytic performance was suggested to be attributed not only to the uniform dispersion of Co₃O₄, but also to the transformation of lattice oxygen in Co₃O₄, which was found to play an important role in the catalytic process by inducing the formation of Co₃O_4−α–OH. Meanwhile, density functional theory (DFT) calculations indicated that the adsorption energy (E_ads) of PMS on Co₃O_4−α–OH was far lower than that on Co₃O₄. Moreover, both radical and non-radical pathways were indicated to be involved during the degradation process. Additionally, the practical application of RHBA@Co₃O₄ was investigated using various antibiotics, actual water environments, and fixed-bed reactors. The results showed that it possessed good practical degradation performance and significantly reduced the toxicity of intermediate products. This work provides a fresh insight into the catalytic mechanism of RHBA800@25Co₃O₄ for PMS activation and wastewater treatment, offering a new perspective on the catalytic mechanism of Co₃O₄-based materials.

Highlights

•	RHBA800@25Co3O4 exhibited ultrafast antibiotics degradation via peroxymonosulfate activation.
•	Inspired formation of Co3O4−α–OH by lattice oxygen induction was explored.
•	Ecological safety of levofloxacin degradation products was verified through antibacterial experiments.

Graphical Abstract

Keywords

Optimized biochar / Co₃O₄ catalyst / Peroxymonosulfate / Antibiotics degradation / Environmental sustainability

References

[1] Bao X, Zhou L, Liu B, Zhang G, Fang Y, Zeng Y. Peroxydisulfate activation by one-step pyrolysis iron-rich sludge biochar for tetracycline removal in water: performance, mechanism and degradation pathway. Biochar, 2025, 7: 87.

[2] Bhagia S, Ďurkovič J, Lagaňa R, Kardošová M, Kačík F, Cernescu A, Schäfer P, Yoo CG, Ragauskas AJ. Nanoscale FTIR and mechanical mapping of plant cell walls for understanding biomass deconstruction. ACS Sustain Chem Eng, 2022, 10: 3016-3026.

[3] Chen C, Liu L, Guo J, Zhou L, Lan Y. Sulfur-doped copper-cobalt bimetallic oxides with abundant Cu(I): a novel peroxymonosulfate activator for chloramphenicol degradation. Chem Eng J, 2019, 361: 1304-1316.

[4] Chen L, Duan J, Du P, Sun W, Lai B, Liu W. Accurate identification of radicals by in-situ electron paramagnetic resonance in ultraviolet-based homogenous advanced oxidation processes. Water Res, 2022, 221. ArticleID: 118747

[5] Chen H, Yu Z, Sun W, Li T, Zhang J, Qiu Z, Younas M. Degradation of tetracycline through peroxymonosulfate activation with Co/Fe-LDH modified magnetic hydrochar: synergistic effect and low toxicity. Sep Purif Technol, 2024, 351. ArticleID: 128023

[6] Chen X, Zhou Y, He J, Pillai SC, Li N, Xu S, Li J, Chen X, Wang H. Elevated efficiency in tartrazine removal from wastewater through boron-doped biochar: enhanced adsorption and persulfate activation. Biochar, 2024, 6: 79.

[7] Gao S, Li T, Zhao X, Hu G, Cui X, Pan L, Wågberg T. Heterogeneous cobalt-based catalysts for boosting peroxymonosulfate activation: a review on cobalt-ion leaching inhibition strategies. Clean Chem Eng, 2025, 11. ArticleID: 100173

[8] Georgin J, Franco D, Meili L, Bonilla-Petriciolet A, Kurniawan T, Imanova G, Demir E, Ali I. Environmental remediation of the norfloxacin in water by adsorption: advances, current status and prospects. Adv Colloid Interface Sci, 2024, 324. ArticleID: 103096

[9] Gong C, Zhao L, Li D, He X, Chen H, Du X, Wang D, Fang W, Zeng X, Li W. In-situ interfacial engineering of Co(OH)₂/Fe₇Se₈ nanosheets to boost electrocatalytic water splitting. Chem Eng J, 2023, 466. ArticleID: 143124

[10] Hu C, Feng J, Zhou N, Zhu J, Zhang S. Hydrochar from corn stalk used as bio-asphalt modifier: high-temperature performance improvement. Environ Res, 2021, 193. ArticleID: 110157

[11] Huang Q, Zhang W, Li F, Zhang M, Li Q, Yang J. Highly efficient peroxymonosulfate activation by molten salt-assisted synthesis of magnetic Mn–Fe₃O₄ supported mesoporous biochar composites for SDZ degradation. ACS EST Water, 2024, 4: 4591-4603.

[12] Islam MdA, Morton DW, Johnson BB, Pramanik BK, Mainali B, Angove MJ. Opportunities and constraints of using the innovative adsorbents for the removal of cobalt(II) from wastewater: a review. Environ Nanotechnol Monit Manag, 2018, 10: 435-456.

[13] Ji X, Huang J-W, Liu W-J, Yu H-Q. Pyrolysis of biomass wastes to N-doped biochar-stabilized Co nanoparticles for efficient pollutant degradation via peroxymonosulfate activation. ACS EST Eng, 2021, 1: 1715-1724.

[14] Jiang J, Shi W, Song S, Hao Q, Fan W, Xia X, Zhang X, Wang Q, Liu C, Yan D. Solvothermal synthesis and electrochemical performance in super-capacitors of Co₃O₄/C flower-like nanostructures. J Power Sources, 2014, 248: 1281-1289.

[15] Li R, Lu X, Yan B, Li N, Chen G, Cheng Z, Hou L, Wang S, Duan X. Sludge-derived biochar toward sustainable peroxymonosulfate activation: regulation of active sites and synergistic production of reaction oxygen species. Chem Eng J, 2022, 440. ArticleID: 135897

[16] Li B, Liu Y, Hu K, Dai Q, Chen C, Duan X, Wang S, Wang Y. Spin‐regulated Fenton‐like catalysis for nonradical oxidation over metal oxide@carbon composites. Adv Funct Mater, 2024, 34. ArticleID: 2401397

[17] Li H, Qin X, Wang K, Ma T, Shang Y. Insight into metal-based catalysts for heterogeneous peroxymonosulfate activation: a critical review. Sep Purif Technol, 2024, 333. ArticleID: 125900

[18] Li Y, Wang K, Wang Z, Wang X, Chu X, Zhang R, Song S, Zhang H, Wang X. Ultra‐fast synthesis of composite oxide‐supported transition metal alloy as an advanced catalyst for ammonia decomposition. Adv Energy Mater, 2025, 15. ArticleID: 2405296

[19] Lu F, Chen Y, Huang J, Lin J, Zhang Y, Xu L, Gan L, Yan M, Gong H. Peroxymonosulfate activation by peanut shell biochar-doped BiFeO₃ composite to remove antibiotic resistant bacteria from aquaculture wastewater. Biochar, 2025, 7: 104.

[20] Meena V, Swami D, Chandel A, Joshi N, Prasher SO. Selected emerging contaminants in water: global occurrence, existing treatment technologies, regulations and associated risk. J Hazard Mater, 2025, 483. ArticleID: 136541

[21] Meng H, Zhou J, Zhang Y, Cui J, Chen Y, Zhong W, Chen Y, Jia CQ. Single-atom Co-N₃ sites induce peroxymonosulfate activation for acetaminophen degradation via nearly 100 % internal electron transfer process. Appl Catal B Environ, 2025, 366. ArticleID: 125038

[22] Mo F, Song C, Zhou Q, Xue W, Ouyang S, Wang Q, Hou Z, Wang S, Wang J. The optimized Fenton-like activity of Fe single-atom sites by Fe atomic clusters–mediated electronic configuration modulation. Proc Natl Acad Sci U S A, 2023, 120. ArticleID: e2300281120

[23] Oberlé K, Capdeville M, Berthe T, Budzinski H, Petit F. Evidence for a complex relationship between antibiotics and antibiotic-resistant Escherichia coli: from medical center patients to a receiving environment. Environ Sci Technol, 2012, 46: 1859-1868.

[24] Patil DJ, Grewal HS. Comparative study of heterogeneous activation of H₂O₂ and peroxymonosulfate over nanoporous ZnFe₂O₄ for dye degradation via batch and continuous-flow channel approach. J Water Process Eng, 2025, 75. ArticleID: 108007

[25] Qi J, Yang X, Pan P-Y, Huang T, Yang X, Wang C-C, Liu W. Interface engineering of Co(OH)₂ nanosheets growing on the KNbO₃ perovskite based on electronic structure modulation for enhanced peroxymonosulfate activation. Environ Sci Technol, 2022, 56: 5200-5212.

[26] Schlumberger C, Thommes M. Characterization of hierarchically ordered porous materials by physisorption and mercury porosimetry—A tutorial review. Adv Mater Interfaces, 2021, 8. ArticleID: 2002181

[27] Song J, Zhao C, Cao X, Cheng W. Enhanced catalytic degradation of antibiotics by peanut shell-derived biochar-Co₃O₄ activated peroxymonosulfate: An experimental and mechanistic study. Process Saf Environ Prot, 2023, 171: 423-436.

[28] Tian W, Lin J, Tian Z, Ncube S, Zhang H, Cortés E, Sun H, Wang S. Biomass native structure into functional carbon-based catalysts for Fenton-like reactions. Adv Funct Mater, 2025.

[29] Wang L, Lan X, Peng W, Wang Z. Uncertainty and misinterpretation over identification, quantification and transformation of reactive species generated in catalytic oxidation processes: a review. J Hazard Mater, 2021, 408. ArticleID: 124436

[30] Wang Y, Peng W, Wang J, Chen G, Li N, Song Y, Cheng Z, Yan B, Hou L, Wang S. Sulfamethoxazole degradation by regulating active sites on distilled spirits lees-derived biochar in a continuous flow fixed bed peroxymonosulfate reactor. Appl Catal B Environ, 2022, 310. ArticleID: 121342

[31] Wang B, Sui Q, Liu H, Yu G, Qu J. Promoting environmental risk assessment and control of emerging contaminants in China. Engineering, 2024, 37: 13-17.

[32] Wang M, Zhang Y, Dong S, Li N, Xu Q, Li H, Lu J, Chen D. Self-floating polymer microreactor for high-efficiency synergistic CO₂ photoreduction and antibiotic degradation in one photoredox cycle. Adv Funct Mater, 2024, 34. ArticleID: 2408831

[33] Wang H, Wang D, Sun C, Zhao X, Xu C, Li Z, Hou Y, Lei L, Yang B, Duan X. Oriented generation of ¹O₂ from peroxymonosulfate via Co₃O₄ facet engineering. Appl Catal B Environ, 2025, 364. ArticleID: 124854

[34] Weng B, Zhang M, Lin Y, Yang J, Lv J, Han N, Xie J, Jia H, Su B-L, Roeffaers M, Hofkens J, Zhu Y, Wang S, Choi W, Zheng Y-M. Photo-assisted technologies for environmental remediation. Nat Rev Clean Technol, 2025, 1: 201-215.

[35] Wu J, Cao M, Tong D, Finkelstein Z, Hoek EMV. A critical review of point-of-use drinking water treatment in the United States. Npj Clean Water, 2021, 4. ArticleID: 40

[36] Yu T, Wang Z, Li H, Zheng K, Luo J, Liu H, Li Y, Ai L, Wang J, Song Y, Ye Z, Zhang Y, Wang H, Chen X, Chen Y. MFe₂O₄/biochar composites in persulfate-advanced oxidation process for antibiotic treatment: a mini review. J Water Process Eng, 2024, 68. ArticleID: 106535

[37] Zhang X, Wei J, Wang C, Wang L, Guo Z, Song Y. Recent advance of Fe-based bimetallic persulfate activation catalysts for antibiotics removal: performance, mechanism, contribution of the key ROSs and degradation pathways. Chem Eng J, 2024, 487. ArticleID: 150514

[38] Zhang J, Xie J-F, Chen J-J, Li W-W, Yang JE, Zheng Y-M, Yu H-Q. Mimicking the protein: hierarchically hydrophilic Co(OH)₂ boosted peroxymonosulfate activation for ultrafast antibiotics degradation. Adv Funct Mater, 2025.

[39] Zhang Z-Q, Duan P-J, Bai C-W, Chen X-J, Wang J, Chen F. Surface-hydroxylated single-atom catalyst with an isolated Co-O-Zn configuration achieves high selectivity in regulating active species. Nat Commun, 2025, 16. ArticleID: 2376

[40] Zhao X, Zhang Z. Heterogeneous peroxymonosulfate-based advanced oxidation mechanisms: new wine in old bottles?. Environ Sci Technol, 2025, 59: 5913-5924.

[41] Zhao J, Li F, Wei H, Ai H, Gu L, Chen J, Zhang L, Chi M, Zhai J. Superior performance of ZnCoO_x/peroxymonosulfate system for organic pollutants removal by enhancing singlet oxygen generation: the effect of oxygen vacancies. Chem Eng J, 2021, 409. ArticleID: 128150

[42] Zhou Q, Song C, Wang P, Zhao Z, Li Y, Zhan S. Generating dual-active species by triple-atom sites through peroxymonosulfate activation for treating micropollutants in complex water. Proc Natl Acad Sci USA, 2023, 120. ArticleID: e2300085120

[43] Zou J, Fan C, Jiang Y, Liu X, Zhou W, Xu H, Huang L. A preliminary study on assessing the Brunauer-Emmett-Teller analysis for disordered carbonaceous materials. Micro Meso Mater, 2021, 327. ArticleID: 111411

Funding

National Key Research & Development Program of China(2021YFA1202700)

International Partnership Program of the Chinese Academy of Sciences(322GJHZ2022035MI)

Fujian Province Natural Science Foundation of China(2025J01257)

Youth Innovation Promotion Association CAS(2022308)

China Postdoctoral Science Foundation(2024M763193)

RIGHTS & PERMISSIONS

The Author(s)