Enhanced electron transfer in Fe–N–C catalysts for nitrobenzene reduction: from electrodes to functional materials

Abstract

The remediation of nitroaromatic-contaminated water systems remains a critical environmental challenge, creating the urgent need for cost-effective, non-precious metal catalysts to increase wastewater biodegradability. In this study, we present an Fe/N-functionalized three-dimensional porous carbon (Fe–N–C) catalyst synthesized via a straightforward pyrolysis approach that enables efficient nitrobenzene (NB) degradation via electrochemical and chemical reduction pathways. The high-temperature pyrolysis process facilitates the iron-catalyzed reconstruction of the carbon matrix, resulting in a hierarchically porous structure with increased graphitization and uniformly distributed macrocyclic Fe–N₄ coordination sites. These structural features give the Fe–N–C catalyst exceptional electron transfer kinetics, catalytic activity, and pH adaptability, surpassing conventional graphite (GR) and nitrogen-doped carbons (NPCs) in NB reduction. Systematic evaluation of the electrochemical reduction performance revealed that the Fe–N–C electrode achieved the highest NB removal efficiency. To further assess the versatility of the catalyst, a functionalized Fe–N–C/zero-valent iron (ZVI) composite was engineered by integrating Fe–N–C as a catalytic layer onto the reductant ZVI. Compared with ZVI alone, this composite markedly increased the NB reduction efficiency. These findings provide valuable insights into the electrochemical reduction process of Fe–N–C and new directions for the rational design of efficient nitrobenzene reduction systems.

Graphical abstract

Keywords

Nitrobenzene / Fe–N–C catalyst / Nitrogen-doped porous carbon / Electrochemical reduction / Functionalized ZVI composite

Highlight

	● Fe–N–C materials enable highly efficient reduction of nitrobenzene (NB).
	● High graphitization and Fe–N4 coordination enhanced the electrochemical performance.
	● Fe–N–C behaves as an n-type semiconductor with high carrier concentration.
	● Fe–N–C/ZVI demonstrates outstanding performance in the reduction of nitrobenzene.

References

[1] Ao X, Zhang W, Li Z S, Lv L, Ruan Y J, Wu H H, Chiang W H, Wang C D, Liu M L, Zeng X C. (2019). Unraveling the high-activity nature of Fe–N–C electrocatalysts for the oxygen reduction reaction: the extraordinary synergy between Fe–N₄ and Fe₄N. Journal of Materials Chemistry A, 7(19): 11792–11801

[2] Bai Y Y, Yun Z C, Xia F, Deng S, Liu Q Y, Wu S X, Han X, Yang Y, Jiang Y H. (2025). Insights on mitigation of chemical clogging of zero-valent iron for nitrobenzene reduction: the role of oxygenated anion modification. Frontiers of Environmental Science & Engineering, 19(9): 117

[3] Cai Z Q, Fu J, Du P H, Zhao X, Hao X D, Liu W, Zhao D Y. (2018). Reduction of nitrobenzene in aqueous and soil phases using carboxymethyl cellulose stabilized zero-valent iron nanoparticles. Chemical Engineering Journal, 332: 227–236

[4] Cao R G, Thapa R, Kim H, Xu X D, Gyu Kim M, Li Q, Park N, Liu M L, Cho J. (2013). Promotion of oxygen reduction by a bio-inspired tethered iron phthalocyanine carbon nanotube-based catalyst. Nature Communications, 4: 2076

[5] Cerrón-Calle G A, Aranda-Aguirre A J, Luyo C, Garcia-Segura S, Alarcón H. (2019). Photoelectrocatalytic decolorization of azo dyes with nano-composite oxide layers of ZnO nanorods decorated with Ag nanoparticles. Chemosphere, 219: 296–304

[6] Chen J, Zuo K C, Li B, Hu J H, Liu W B, Xia D S, Lin L, Liang J J, Li X Y. (2022). Fungal hypha-derived freestanding porous carbon pad as a high-capacity electrode for water desalination in membrane capacitive deionization. Chemical Engineering Journal, 433: 133781

[7] Cheng T Y, Yu H, Peng F, Wang H J, Zhang B S, Su D S. (2016). Identifying active sites of CoNC/CNT from pyrolysis of molecularly defined complexes for oxidative esterification and hydrogenation reactions. Catalysis Science & Technology, 6(4): 1007–1015

[8] Chong S, Song Y L, Zhao H, Zhang G M, Li J. (2016). Ultrasound/Zn⁰ for aqueous 4-nitrobenzoic acid degradation. Desalination and Water Treatment, 57(52): 24990–24998

[9] Cui X Y, Yang S B, Yan X X, Leng J G, Shuang S, Ajayan P M, Zhang Z J. (2016). Pyridinic-nitrogen-dominated graphene aerogels with Fe–N–C coordination for highly efficient oxygen reduction reaction. Advanced Functional Materials, 26(31): 5708–5717

[10] Daems N, Sheng X, Vankelecom I F J, Pescarmona P P. (2014). Metal-free doped carbon materials as electrocatalysts for the oxygen reduction reaction. Journal of Materials Chemistry A, 2(12): 4085–4110

[11] Daems N, Wouters J, Van Goethem C, Baert K, Poleunis C, Delcorte A, Hubin A, Vankelecom I F J, Pescarmona P P. (2018). Selective reduction of nitrobenzene to aniline over electrocatalysts based on nitrogen-doped carbons containing non-noble metals. Applied Catalysis B: Environmental, 226: 509–522

[12] Dong J, Zhao Y S, Zhao R, Zhou R. (2010). Effects of pH and particle size on kinetics of nitrobenzene reduction by zero-valent iron. Journal of Environmental Sciences, 22(11): 1741–1747

[13] Fan P, Zhang X J, Deng H H, Guan X H. (2021). Enhanced reduction of p-nitrophenol by zerovalent iron modified with carbon quantum dots. Applied Catalysis B: Environmental, 285: 119829

[14] Haigler B E, Spain J C. (1991). Biotransformation of nitrobenzene by bacteria containing toluene degradative pathways. Applied and Environmental Microbiology, 57(11): 3156–3162

[15] Hu J P, Liu G L, Li H, Luo H P, Zhang R D. (2022). Synergistic effect of bioanode and biocathode on nitrobenzene removal: microbial community structure and functions. Science of the Total Environment, 833: 155190

[16] Jiang W J, Gu L, Li L, Zhang Y, Zhang X, Zhang L J, Wang J Q, Hu J S, Wei Z D, Wan L J. (2016). Understanding the high activity of Fe-N-C electrocatalysts in oxygen reduction: Fe/Fe₃C nanoparticles boost the activity of Fe-N_x. Journal of the American Chemical Society, 138(10): 3570–3578

[17] Jiao L, Wan G, Zhang R, Zhou H, Yu S H, Jiang H L. (2018). From metal-organic frameworks to single-atom fe implanted n-doped porous carbons: efficient oxygen reduction in both alkaline and acidic media. Angewandte Chemie International Edition, 57(28): 8525–8529

[18] Jin M, Liu Y Y, Zhang X, Wang J L, Zhang S B, Wang G Z, Zhang Y X, Yin H J, Zhang H M, Zhao H J. (2021). Selective electrocatalytic hydrogenation of nitrobenzene over copper-platinum alloying catalysts: Experimental and theoretical studies. Applied Catalysis B: Environmental, 298: 120545

[19] Lei Z C, Huang Z Y, Lin Y M, Liu Y W, Yan Z, Zheng W X, Ma H X, Dang Z, Feng C H. (2022). Boosting the oxidative capacity of the Fe⁰/O₂ system via an air-breathing cathode. Journal of Hazardous Materials, 438: 129552

[20] Lin L L, Yao S Y, Gao R, Liang X, Yu Q L, Deng Y C, Liu J J, Peng M, Jiang Z, Li S W. . (2019). A highly CO-tolerant atomically dispersed Pt catalyst for chemoselective hydro-genation. Nature Nanotechnology, 14(4): 354–361

[21] Liu C, Zhang A Y, Pei D N, Yu H Q. (2016a). Efficient electrochemical reduction of nitrobenzene by defect-engineered TiO_2–x single crystals. Environmental Science & Technology, 50(10): 5234–5242

[22] Liu D Q, Wei B, Zhang C, Li Q W. (2025). Electrochemically regulated cerium-based electrode for enhanced phosphate adsorption and desorption process. Separation and Purification Technology, 360: 131025

[23] Liu W G, Zhang L L, Yan W S, Liu X Y, Yang X F, Miao S, Wang W T, Wang A Q, Zhang T. (2016b). Single-atom dispersed Co–N–C catalyst: structure identification and performance for hydrogenative coupling of nitroarenes. Chemical Science, 7(9): 5758–5764

[24] Liu Y W, Gu K L, Zhang J H, Li J X, Qian J S, Shen J Y, Guan X H. (2024). Partial aging can counter-intuitively couple with sulfidation to improve the reactive durability of zerovalent iron. Frontiers of Environmental Science & Engineering, 18(2): 14

[25] Mahata N, Cunha A F, Órfão J J M, Figueiredo J L. (2008). Hydrogenation of nitrobenzene over nickel nanoparticles stabilized by filamentous carbon. Applied Catalysis A: General, 351(2): 204–209

[26] Nichela D A, Berkovic A M, Costante M R, Juliarena M P, Einschlag F S G. (2013). Nitrobenzene degradation in Fenton-like systems using Cu(II) as catalyst. Comparison between Cu(II)- and Fe(III)-based systems. Chemical Engineering Journal, 228: 1148–1157

[27] Qu K G, Zheng Y, Zhang X X, Davey K, Dai S, Qiao S Z. (2017). Promotion of electrocatalytic hydrogen evolution reaction on nitrogen-doped carbon nanosheets with secondary heteroatoms. ACS Nano, 11(7): 7293–7300

[28] Song J J, Huang Z F, Pan L, Li K, Zhang X W, Wang L, Zou J J. (2018). Review on selective hydrogenation of nitroarene by catalytic, photocatalytic and electrocatalytic reactions. Applied Catalysis B: Environmental, 227: 386–408

[29] Wang B S, Zhao P Y, Zhang X N, Zhang Y, Liu Y M. (2024). Three-dimensional electro-Fenton system with iron-carbon packing as a particle electrode for nitrobenzene wastewater treatment. Frontiers of Environmental Science & Engineering, 18(11): 138

[30] Wang H B, Maiyalagan T, Wang X. (2012). Review on recent progress in nitrogen-doped graphene: synthesis, characterization, and its potential applications. ACS Catalysis, 2(5): 781–794

[31] WangJLuHZhouYSongYLiuG FFengY J (2013). Enhanced biotransformation of nitrobenzene by the synergies of Shewanella species and mediator-functionalized polyurethane foam. Journal of Hazardous Materials, 252–253: 252–253

[32] Wang Y C, Liu Y Y, Zhao Z Y, Zheng Z K, Balu A M, Luque R, Yan K. (2023a). Topological iron silicide with H^* intermediate modulated surface for efficient electrocatalytic hydrogenation of nitrobenzene in neutral medium. Materials Today, 66: 84–91

[33] Wang Y F, Hou Y H, Wang Q F, Wang Y T. (2021). The elucidation of the biodegradation of nitrobenzene and p-nitrophenol of nitroreductase from Antarctic psychrophile Psychrobacter sp. ANT206 under low temperature. Journal of Hazardous Materials, 413: 125377

[34] WangY XSunH QDuanX GAngH MTadéM OWangS B (2015). A new magnetic nano zero-valent iron encapsulated in carbon spheres for oxidative degradation of phenol. Applied Catalysis B: Environmental, 172–173: 172–173

[35] Wang Z, Zhang W J, Wang Z W, Chang J. (2023b). Ozonation of aromatic monomer compounds in water: factors determining reaction outcomes. Frontiers of Environmental Science & Engineering, 17(5): 54

[36] Wang Z L, Li C L, Yamauchi Y. (2016). Nanostructured nonprecious metal catalysts for electrochemical reduction of carbon dioxide. Nano Today, 11: 373–391

[37] Yang X, Xia D S, Kang Y Q, Du H D, Kang F Y, Gan L, Li J. (2020). Unveiling the axial hydroxyl ligand on Fe-N₄-C electrocatalysts and its impact on the pH-dependent oxygen reduction activities and poisoning kinetics. Advanced Science, 7(12): 2000176

[38] Yin W Z, Wu J H, Huang W L, Wei C H. (2015). Enhanced nitrobenzene removal and column longevity by coupled abiotic and biotic processes in zero-valent iron column. Chemical Engineering Journal, 259: 417–423

[39] Yu D, Jiang Q, Zhu H Q, Chen Y, Xu L X, Ma H, Pu S Y. (2025). Electrochemical reduction for chlorinated hydrocarbons contaminated groundwater remediation: mechanisms, challenges, and perspectives. Water Research, 274: 123149

[40] Zhang E R, Wang F, Zhai W J, Scott K, Wang X, Diao G W. (2017). Efficient removal of nitrobenzene and concomitant electricity production by single-chamber microbial fuel cells with activated carbon air-cathode. Bioresource Technology, 229: 111–118

[41] Zhang Q S, Bu J H, Wang J D, Sun C Y, Zhao D Y, Sheng G Z, Xie X W, Sun M, Yu L. (2020). Highly efficient hydrogenation of nitrobenzene to aniline over Pt/CeO₂ catalysts: the shape effect of the support and key role of additional Ce³⁺ sites. ACS Catalysis, 10(18): 10350–10363

[42] Zhao X Y, Li A L, Quan X, Chen S, Yu H T, Zhang S S. (2020). Efficient electrochemical reduction of nitrobenzene by nitrogen doped porous carbon. Chemosphere, 238: 124636

[43] Zhu S J, Wang Z J, Chen Y H, Lu T R, Li J, Wang J C, Jin H L, Lv J J, Wang X, Wang S. (2024). Recent progress toward electro-catalytic conversion of nitrobenzene. Small Methods, 8(8): 2301307

RIGHTS & PERMISSIONS

Higher Education Press 2025