Cage-like ulva biochar confined synthesis of Fe₃O₄/ZnO heterojunction nanoparticles for synergistic adsorption and photocatalytic degradation of PFOA

Abstract

Perfluorooctanoic acid (PFOA) has emerged as a new urgent pollutant in aquatic environments due to its high persistence and ecotoxicity. In photocatalytic degradation systems, challenges such as rapid recombination of electron–hole pairs (e⁻/h⁺), short lifespans of reactive oxygen species (ROS), and insufficient ROS generation hinder the efficient degradation of PFOA. This study presents a novel "scallop cage" architecture, constructed using Ulva biochar to create confined spaces that encapsulate the Fe₃O₄/ZnO heterojunction. This approach not only controls the crystal size of the Fe₃O₄/ZnO heterojunction but also confines the degradation reactions to a specific space, significantly shortening the mass transfer distance for ROS and effectively mitigating their rapid deactivation in aqueous-phase degradation processes. Furthermore, the confinement effect enhances the generation of multiple reactive species (·O₂⁻, ·OH, ¹O₂, and h⁺). The optimized FZS@UBC-2 composite photocatalyst achieved a PFOA removal efficiency of 97.53%. In practical applications, FZS@UBC-2 efficiently decomposes PFOA in complex aqueous matrices and can be easily recovered using an external magnetic field. This work not only expands the application of algae-derived biochar in advanced oxidation processes but also offers a sustainable strategy for addressing persistent organic pollutants in aquatic environments.

Keywords

Biochar / Confinement synthesis / Adsorption-photocatalysis synergistic degradation / Emerging contaminants (ECs) / Perfluorooctanoic acid (PFOA)

References

[1] Amir M, Fazal T, Iqbal J, Din AA, Ahmed A, Ali A, Razzaq A, Ali Z, Rehman MSU, Park YK. Integrated adsorptive and photocatalytic degradation of pharmaceutical micropollutant, ciprofloxacin employing biochar-ZnO composite photocatalysts. J Ind Eng Chem, 2025, 115: 171-182

[2] Bahiraei H, Azarakhsh S, Ghasemi S. Ternary CoFe₂O₄/g-C₃N₄/ZnO heterostructure as an efficient and magnetically separable visible-light photocatalyst: characterization, dye purification, and mechanism. Ceram Int, 2023, 49: 21050-21059

[3] Brindhadevi K, Kim TP, Alharbi SA, Ramesh MD, Lee J, Bharathi D. Enhanced photocatalytic degradation of polycyclic aromatic hydrocarbons (PAHs) using NiO nanoparticles. Environ Res, 2024, 252 118454

[4] Cai S, Zhang Q, Wang Z, Hua S, Ding D, Cai T, Zhang R. Pyrrolic N-rich biochar without exogenous nitrogen doping as a functional material for bisphenol A removal: performance and mechanism. Appl Catal B, 2021, 291 120093

[5] Chen S, Jiao XC, Gai N, Li XJ, Wang XC, Lu GH, Piao HT, Rao Z, Yang YL. Perfluorinated compounds in soil, surface water, and groundwater from rural areas in Eastern China. Environ Pollut, 2016, 211: 124-131

[6] Chen L, Wang X, Shi G, Lu G, Wang Y, Xie X, Chen D, Sun J. The regulation of Lewis acid/basic sites in NaFe bimetal MOXs for the controllable photocatalytic degradation of electron-rich/deficient VOCs. Appl Catal B, 2023, 334 122850

[7] Chetverikov SP, Sharipov DA, Korshunova TY, Loginov ON. Degradation of perfluorooctanyl sulfonate by strain pseudomonas plecoglossicida 2.4-D. Appl Biochem Microbiol, 2017, 53: 533-538

[8] Cotruvo JA, Goldhaber SB, Cohen AJ. EPA's unprecedented interim drinking water health advisories for PFOA and PFOS. Ground Water, 2020, 61: 301-303

[9] Dhore R, Murthy GS. Per/polyfluoroalkyl substances production, applications and environmental impacts. Bioresour Technol, 2021, 341 125808

[10] Ding S, Wu S, Fang N, Chu Y, Wang P, Ding L. Design and synthesis of porous nano-confined catalysts for VOCs oxidation: a critical review based on pollutant sorts. Sep Purif Technol, 2025, 352 128158

[11] Edalati K, Shakiba A, Khaki J, Zebarjad S. Low-temperature hydrothermal synthesis of ZnO nanorods: effects of zinc salt concentration, various solvents and alkaline mineralizers. Mater Res Bull, 2016, 74: 374-376

[12] Essa RA, El-Aal MA, Sedky A, Zeid EFA, Amin S. ZnO NPs-modified biochar derived from banana peels for adsorptive removal of methylene blue from water. J Mol Struct, 2025, 1321 139821

[13] Fenton SE, Ducatman A, Boobis A, Dewitt JC, Roberts SM. Per- and polyfluoroalkyl substance toxicity and human health review: current state of knowledge and strategies for informing future research. Environ Toxicol Chem, 2020, 40: 606-630

[14] Grifoni E, Piccini G, Lercher J, Glezakou VA, Rousseau R, Parrinello M. Confinement effects and acid strength in zeolites. Nat Commun, 2021, 114: 2630

[15] Guo D, Liu Y, Ji H, Wang CC, Chen B, Shen C, Li F, Wang Y, Lu P, Liu W. Silicate-enhanced heterogeneous flow-through electro-Fenton system using iron oxides under nanoconfinement. Environ Sci Technol, 2021, 55: 4045-4053

[16] Han J, Guan J. Controllable synthesis of dual-atom catalysts by a confinement-pyrolysis strategy. Chin J Catal, 2023, 49: 1-4

[17] Hori H, Nagaoka Y, Yamamoto A, Sano T, Yamashita N. Efficient decomposition of environmentally persistent perfluorooctanesulfonate and related fluorochemicals using zerovalent iron in subcritical water. Environ Sci Technol, 2006, 40: 1049-1054

[18] Jia Z, Yang Y, Yang C, Wang D. Magnetic γ-Fe₂O₃/ZnO@CNTs synthesized by a green precipitation method for the degradation of aniline through photocatalysis coupling catalytic ozonation. Appl Surf Sci, 2024, 659 159866

[19] Khan I, Qurashi A, Berdiyorov G, Iqbal N, Fuji K, Yamani Z. Single-step strategy for the fabrication of GaON/ZnO nanoarchitectured photoanode their experimental and computational photoelectrochemical water splitting. Nano Energy, 2018, 44: 23-33

[20] Li K, Gao P, Xiang P, Zhang X, Cui X, Ma L. Molecular mechanisms of PFOA-induced toxicity in animals and humans: implications for health risks. Environ Int, 2016, 99: 43-54

[21] Li M, Yu Z, Liu Q, Sun L, Huang W. Photocatalytic decomposition of perfluorooctanoic acid by noble metallic nanoparticles modified TiO₂. Chem Eng J, 2016, 286: 232-238

[22] Li Y, Li Y, Yin Y, Xia D, Ding H, Ding C, Wu J, Yan Y, Liu Y, Chen N, Wong P, Lu A. Facile synthesis of highly efficient ZnO/ZnFe₂O₄ photocatalyst using earth-abundant sphalerite and its visible light photocatalytic activity. Appl Catal B, 2018, 226: 324-336

[23] Li S, Zhao Y, Du L, He Y, Wang R, Guo Y, Wang C, Tian T, Wang L, Liu H. Moisture-assisted molecular sieve-confined synthesis of lead-free CsAgCl₂ perovskite-derivative nanocrystals. Chem Eng J, 2024, 482 148966

[24] Liu R, Huang H, Li H, Liu Y, Zhong J, Li Y, Zhang S, Kang Z. Metal nanoparticle/carbon quantum dot composite as a photocatalyst for high-efficiency cyclohexane oxidation. ACS Catal, 2014, 11: 328-336

[25] Liu J, Guo C, Wu N, Li C, Qu R, Wang Z, Jin R, Qiao Y, He Z, Lu J, Feng X, Zhang Y, Wang A, Gao J. Efficient photocatalytic degradation of PFOA in N-doped In₂O₃/simulated sunlight irradiation system and its mechanism. Chem Eng J, 2022, 435 134627

[26] Liu H, Shi M, Yang R, Wang Y, Li H, Su Q, Wang T, Wang S. Enhanced photocatalytic hydrogen evolution via yolk–heteroshell TiO₂@TiO₂/SiO₂ nanoreactor with confined Pt nanoparticles. Chem Eng J, 2024, 499 156118

[27] Luo J, Chen Y, Huang H, Ma R, Ma N, Yan F, Xu J, Zhang J, Chen J, Sun S. Microwave-coordinated KOH directionally modulated N/O co-doped porous biochar from Enteromorpha and its structure–effect relationships in efficient CO₂ capture. Chem Eng J, 2023, 473 145279

[28] Lv C, Jiao P, Xin H, Wu L, Ouyang G, Hou X. Earth-abundant insulator hydroxyapatite-based composite for full-spectrum photocatalytic degradation of 2, 4- dichlorophenol. Appl Catal B, 2024, 340 123248

[29] Magnier L, Cossard G, Martin V, Pascal C, Roche V, Sibert E, Shchedrina I, Bousquet R, Parry V, Chatenet M. Fe–Ni-based alloys as highly active and low-cost oxygen evolution reaction catalyst in alkaline media. Nat Mater, 2024, 23: 252-261

[30] Malhotra M, Soni V, Kumar R, Tarannum SP, Thakur S, Le QV, Nguyen LH, Nguyen VH, Raizada P. MOFs-based S-scheme heterojunction photocatalysts: Challenges and prospects to break the selectivity limitation for intensified C₁ products in CO₂ photoreduction. Chem Eng J, 2024, 506 160238

[31] Park SH, Kim S, Park JW, Kim S, Cha W, Lee J. In-situ and wavelength-dependent photocatalytic strain evolution of a single Au nanoparticle on a TiO₂ film. Nat Commun, 2024, 15: 5416

[32] Qiu Z, Wang Y, Bi X, Zhou T, Zhou J, Zhao J, Miao Z, Yi W, Fu P, Zhuo S. Biochar-based carbons with hierarchical micro-meso-macro porosity for high rate and long cycle life supercapacitors. J Power Sources, 2018, 376: 82-90

[33] Qu S, Yuan Y, Yang X, Xu H, Mohamed AK, Zhang J, Zhao C, Liu L, Wang B, Wang X, Rinklebe J, Li YC, Wang S. Carbon defects in biochar facilitated nitrogen doping: the significant role of pyridinic nitrogen in peroxymonosulfate activation and ciprofloxacin degradation. Chem Eng J, 2022, 441 135864

[34] Rana P, Soni V, Sharma S, Poonia K, Patial S, Singh P, Selvasembian R, Chaudhary V, Hussain CM, Raizada P. Harnessing nitrogen doped magnetic biochar for efficient antibiotic adsorption and degradation. J Ind Eng Chem, 2025, 148: 174-195

[35] Senevirathna ST, Tanaka S, Fujii S, Kunacheva C, Harada H, Shivakoti BR, Okamoto R. A comparative study of adsorption of perfluorooctane sulfonate (PFOS) onto granular activated carbon, ion-exchange polymers and non-ion-exchange polymers. Chemosphere, 2024, 80: 647-651

[36] Shan S, Lv Z, Wu HA. Novel readily recyclable Fe3O4/ZnO/loofah biochar composite for efficient degradation of organic pollutants under visible light. Mater Sci Eng B Solid State Mater Adv Appl, 2024, 303 117272

[37] Tang L, Meng GD, Deng H, Bao H. Confinement Catalysis with 2D Materials for Energy Conversion. Adv Mater, 2019, 31: 1901996

[38] Tian D, Cheng J, Jia M, Li R, Liu Z, Chen Q. Re-insight of the degradation of perfluorooctanoic acid (PFOA) through three-dimensional rotating gliding arc plasma. Process Saf Environ Prot, 2024, 194: 231-245

[39] Velumani M, Rajamohan S, Pandey A, Pham N, Nguyen V, Hoang A. Nanocomposite from tannery sludge-derived biochar and Zinc oxide nanoparticles for photocatalytic degradation of Bisphenol A toward dual environmental benefits. Sci Total Environ, 2024, 907 167896

[40] Wang JS, Wu K, Yin C, Li K, Huang Y, Ruan J, Feng X, Hu P, Su CY. Cage-confined photocatalysis for wide-scope unusually selective [2 + 2] cycloaddition through visible-light triplet sensitization. Nat Commun, 2020, 11: 4675

[41] 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, 2022, 310 121342

[42] Wang C, Zhou S, Cui Q, Zhang M, Zheng L, Li S, Liu X, Chen M. Self-floating g-C₃N₄/h-BN/Au photo-thermal catalysts with unprecedented thermostability at solar-activated heating condition for reusable degradation of organic pollutants. Appl Catal B, 2024, 343 123491

[43] Wang R, Yin Z, Yang G, Zha Q, Xiong C, Xie Y, Xu J, Luo Y, Hong Z, Xie C, Xue M. Highly efficient multifunctional 3D polyurethane sponge with photothermal responsiveness for efficient oil-water separation and microplastic extraction. Desalination, 2025, 601 118604

[44] Wee SY, Aris AZ. Environmental impacts, exposure pathways, and health effects of PFOA and PFOS. Ecotoxicol Environ Saf, 2023, 267 115663

[45] Wei S, Zhang J, Zhang L, Wang Y, Sun H, Hua X, Guo Z, Dong D. Efficient generation of singlet oxygen for photocatalytic degradation of antibiotics: synergistic effects of Fe spin state reduction and energy transfer. Appl Catal B, 2024, 358 124406

[46] Wu Y, Ye C, Yu L, Liu Y, Huang J, Bi J, Xue L, Sun J, Yang J, Zhang W, Wang X, Xiong P, Zhu J. Soft template-directed interlayer confinement synthesis of a Fe-Co dual single-atom catalyst for Zn-air batteries. Energy Storage Mater, 2022, 45: 805-813

[47] Xin S, Liu G, Ma X, Gong J, Ma B, Yan Q, Chen Q, Ma D, Zhang G, Gao M, Xin Y. High efficiency heterogeneous Fenton-like catalyst biochar modified CuFeO₂ for the degradation of tetracycline: economical synthesis, catalytic performance and mechanism. Appl Catal B, 2021, 280 119386

[48] Yang G, Yin Z, Han X, Hong Z, Xie C, Ma Y, Xu J, Xue M. Corrugated janus hydrogel-based solar evaporator with enhanced light-trapping nanostructures inspired by corn bracts for efficient seawater desalination. Chem Eng J, 2016, 512 162459

[49] Yang G, Zhang Y, Yin Z, Deng Y, Li Z, Xie Y, Chen Y, Yang C, Yang H, Luo Y, Hong Z, Xue M. Robust mussel-inspired LBL carbon nanotube-based superhydrophobic polyurethane sponge for efficient oil–water separation utilizing photothermal effect. Fuel, 2025, 381 133353

[50] Yang G, Yin Z, Zha Q, Wang R, Xie Y, Chen Y, Hong Z, Luo Y, Xue M. A typha orientalis-inspired 3D Janus solar evaporator with controllable wettability for highly efficient and stable solar desalination. Desalination, 2025, 595 118318

[51] Yang G, Yin Z, Deng Y, Li Z, Chen Y, Xiao W, Hong Z, Luo Y, Xie C, Xue M. Fabrication of flexible multifunctional graphene-based composite membrane with improved hydrophobicity and thermal conductivity characters for thermal management. Colloids Surf A Physicochem Eng Asp, 2025, 704 135494

[52] Yin Z, Chen X, Chen Z, Song H, Lv P, Xue M, Li H. Superhydrophobic photocatalytic self-cleaning nanocellulose-based strain sensor for full-range human motion monitoring. Adv Mater Interfaces, 2023, 10(33 2300350

[53] Yin Z, Yu Q, Chen H, Chen X, Liu K, Li M, Yang X, Chen Y, Xie Y, Luo Y, Xue M. Ce-MOF-based superhydrophobic nancellulose composite membrane with rapid photocatalytic properties and continuous oil-water separation. Int J Biol Macromol, 2025, 308 142520

[54] Zhang D, Zuo X, Gao W, Huang H, Zhang H, Cong T, Yang S, Zhang J, Pan L. Recyclable ZnO/Fe₃O₄ nanocomposite with piezotronic effect for high performance photocatalysis. Mater Res Bull, 2022, 148 111677

[55] Zhu J, Zhu Z, Zhang H, Lu H, Zhang W, Qiu Y, Zhu L, Küppers S. Calcined layered double hydroxides/reduced graphene oxide composites with improved photocatalytic degradation of paracetamol and efficient oxidation-adsorption of As (III). Appl Catal B, 2018, 225: 550-562

[56] Zou Y, Xiao K, Qin Q, Shi JW, Heil T, Markushyna Y, Jiang L, Antonietti M, Savateev A. Enhanced organic photocatalysis in confined flow through a carbon nitride nanotube membrane with conversions in the millisecond regime. ACS Nano, 2021, 15: 6551-6561

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