Abstract：Carbon nanotubes (CNT) were modified using concentrated sulfuric acid, and the modified CNTs (MCNT) were employed as the support for iron (MCNT-Fe) to construct a heterogeneous electro-Fenton system with the cathode of MCNT-Fe for the removal of levofloxacin (LFV). Characterization results of the cathode material by SEM, XPS, XRD, and FTIR revealed that the loaded iron existed in the form of nano-Fe2O3 with the majority of particles (>80%) being smaller than 8nm, while various oxygen-containing functional groups were found on the surface of MCNT. Analysis of the cyclic voltammetry curves (CV) and impedance spectra (EIS) of the cathode materials indicated that the MCNT-Fe cathode exhibited greater oxygen reduction activity and stronger electron transfer capability than CNT and MCNT. Consequently, the electro-Fenton with the MCNT-Fe cathode demonstrated higher LFV removal efficiency. Under optimized conditions, the LFV removal efficiency could reach 92.7%~95.7% in range of pH 3~9 after 240min reaction. The Singlet oxygen (1O2) was identified as the primary reactive oxygen species (contributing to 64.6%). Furthermore, the MCNT-Fe cathode exhibited stable performance during multiple cycles with LFV removal rate of 89.3% after six cycles. The expanded pH range, stable cathode performance, and excellent LFV removal performance make the electro-Fenton method with MCNT-Fe cathode highly suitable for practical application. The proposed mechanism for the formation of 1O2 provides theoretical support for its application.
[1] Millanao A R, Mora A Y, Villagra N A, et al. Biological effects of quinolones: A family of broad-spectrum antimicrobial agents [J]. Molecules, 2021,26(23):7153. [2] Grenni P, Ancona V, Caracciolo A B. Ecological effects of antibiotics on natural ecosystems: A review [J]. Microchemical Journal, 2018,136:25-39. [3] Brillas E, Sires I, Oturan M A. Electro-Fenton process and related electrochemical technologies based on Fenton’s reaction chemistry [J]. Chemical Reviews, 2009,109(12):6570-6631. [4] Zeng H, Zhang G, Ji Q, et al. pH-independent production of hydroxyl radical from atomic H*-mediated electrocatalytic H2O2 reduction: A green Fenton process without byproducts [J]. Environmental Science & Technology, 2020,54(22):14725-14731. [5] Mazzucato M, Durante C. Insights on oxygen reduction reaction to H2O2: the role of functional groups and textural properties on the activity and selectivity of doped carbon electrocatalysts [J]. Current Opinion in Electrochemistry, 2022,35:101051. [6] Zhou W, Xie L, Gao J, et al. Selective H2O2 electrosynthesis by O-doped and transition-metal-O-doped carbon cathodes via O2 electroreduction: A critical review [J]. Chemical Engineering Journal, 2021,410:128368. [7] Ding Y, Zhou W, Gao J, et al. H2O2 Electro generation from O2 Electroreduction by N-Doped Carbon Materials: A Mini-Review on Preparation Methods, Selectivity of N Sites, and Prospects [J]. Advanced Materials Interfaces, 2021,8(10):2002091. [8] Brillas E, Sirés I, Oturan M A. Electro-Fenton process and related electrochemical technologies based on Fenton’s reaction chemistry [J]. Chemical Reviews, 2009,109(12):6570-6631. [9] De Volder M F L, Tawfick S H, Baughman R H, et al. Carbon nanotubes: present and future commercial applications [J]. Science, 2013,339(6119):535-539. [10] Brillas E, Sirés I, Oturan M A. Electro-Fenton process and related electrochemical technologies based on Fenton’s reaction chemistry [J]. Chemical Reviews, 2009,109(12):6570-6631. [11] Gao G, Zhang Q, Hao Z, et al. Carbon nanotube membrane stack for flow-through sequential regenerative electro-Fenton [J]. Environmental Science & Technology, 2015,49(4):2375-2383. [12] Jiang Y, Ni P, Chen C, et al. Selective electrochemical H2O2 production through two-electron oxygen electrochemistry [J]. Advanced Energy Materials, 2018,8(31):1801909. [13] Gao G, Zhang Q, Hao Z, et al. Carbon nanotube membrane stack for flow-through sequential regenerative electro-Fenton [J]. Environmental Science & Technology, 2015,49(4):2375-2383. [14] Jiang Y, Ni P, Chen C, et al. Selective electrochemical H2O2 production through two-electron oxygen electrochemistry [J]. Advanced Energy Materials, 2018,8(31):1801909. [15] Liu Y, Xie J, Ong C N, et al. Electrochemical wastewater treatment with carbon nanotube filters coupled with in situ generated H2O2 [J]. Environmental Science: Water Research & Technology, 2015,1(6): 769-778. [16] Isarain-Chávez E, de la Rosa C, Martínez-Huitle C A, et al. On-site hydrogen peroxide production at pilot flow plant: application to electro-Fenton process [J]. International Journal of Electrochemical Science, 2013,8(3):3084-3094. [17] Zhou M, Yu Q, Lei L. The preparation and characterization of a graphite-PTFE cathode system for the decolorization of CI Acid Red 2[J]. Dyes and Pigments, 2008,77(1):129-136. [18] Enami S, Sakamoto Y, Colussi A J. Fenton chemistry at aqueous interfaces [J]. Proceedings of the National Academy of Sciences, 2014,111(2):623-628. [19] Zhang S, Sun M, Hedtke T, et al. Mechanism of heterogeneous Fenton reaction kinetics enhancement under nanoscale spatial confinement [J]. Environmental Science & Technology, 2020,54(17):10868-10875. [20] Yi Q, Ji J, Shen B, et al. Singlet oxygen triggered by superoxide radicals in a molybdenum catalytic Fenton reaction with enhanced REDOX activity in the environment [J]. Environmental Science & Technology, 2019,53(16):9725-9733. [21] Wang P, Zhou X, Wang J, et al. Heterogeneous electro-Fenton system with Co/N-GO modified cathode to degrade phenolic organic pollutants: The main role of singlet oxygen [J]. Journal of Water Process Engineering, 2023,53:103850. [22] Zhao Y, Sun M, Wang X, et al. Janus electrocatalytic flow-through membrane enables highly selective singlet oxygen production [J]. Nature communications, 2020,11(1):6228. [23] Xing H, Feng F, Guo B, et al. Improvement of sludge dewatering performance by electro-Fenton process with activated carbon fiber cathode [J] Environmental protection of Chemical Industry, 2023, 43(5):668-675. [24] Gopiraman M, Karvembu R, Kim I S. Highly active, selective, and reusable RuO2/SWCNT catalyst for Heck olefination of aryl halides [J]. ACS Catalysis, 2014,4(7):2118-2129. [25] Wu T, Zhang Y, Lin Y, et al. Preparation of CNT-Fe/Zn catalyst and its catalytic ozonation performance on the removal of dibutyl phthalate at a wide pH range [J/OL]. China Environmental Science,https://doi.org/10.19674/j.cnki.issn1000-6923.20230928.006. [26] Chen W, Pan X, Bao X, et al. Tuning of redox properties of iron and iron oxides via encapsulation within carbon nanotubes. J. Am. Chem. Soc. 2007,129,7421−7426. [27] Xie J, Wang Z, Gao W, et al. Cobalt-based gas diffusion electrodes enhance the E-Fenton for sulfathiazole sodium treatment [J]. China Environmental Science, 2023,43(1):122-131. [28] Zhou M, Yu Q, Lei L. The preparation and characterization of a graphite-PTFE cathode system for the decolorization of CI Acid Red 2[J]. Dyes and Pigments, 2008,77(1):129-136. [29] Haag W R, Yao C C D. Rate constants for reaction of hydroxyl radicals with several drinking water contaminants [J]. Environmental Science & Technology, 1992,26(5):1005-1013. [30] Ghorbani P, Mojtabapour Z S, Ganjali F, et al. A Light-Driving Magnetic Nanocomposite Based on Zn/Fe/Cu Embedded in HKUST-1Applied for Adsorption/Degradation of Indigo Carmine and Pathogens [J]. Environmental Technology & Innovation, 2023:103439. [31] Fu Q, Li W X, Yao Y, et al. Interface-confined ferrous centers for catalytic oxidation [J]. Science, 2010,328(5982):1141-1144. [32] Guo D, Liu Y, Ji H, et al.Silicate-enhanced heterogeneous flow- through electro- Fenton system using iron oxides under nanoconfinement [J]. Environmental Science & Technology, 2021, 55(6):4045-4053. [33] MacManus-Spencer L A, McNeill K. Quantification of singlet oxygen production in the reaction of superoxide with hydrogen peroxide using a selective chemiluminescent probe [J]. Journal of the American Chemical Society, 2005,127(25):8954-8955. [34] Zhang J, He X, Li X, et al.《Determination of trace iron in water by phenanthroline spectrophotometry》Training improvement research [J]. Journal of Green Science and Technology, 2020,(21):271-272,274.
