Magnetically enhanced Fenton-like processes by nanofibers: real-time observation of tetracycline degradation in pig manure wastewater

This work investigates the degradation of tetracycline (TC) in pig manure wastewater by a magnetically assisted heterogeneous Fenton-like process using MnFe₂O₄ magnetic nanoparticles (MNPs) embedded into polyacrylonitrile nanofibers (MNFs), resulting in flexible mats with high magnetic heating capacity (SLP ≈ 2.2 kW/g in air). TC degradation was monitored in real time by UV - Vis spectroscopy, showing that the MNF/H₂O₂ system could reduce the TC concentration from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>[</mml:mo><mml:mrow><mml:mrow><mml:mi>TC</mml:mi></mml:mrow></mml:mrow><mml:msub><mml:mo>]</mml:mo><mml:mn>0</mml:mn></mml:msub><mml:mo>≈</mml:mo><mml:mn>6</mml:mn><mml:mrow><mml:mspace></mml:mspace><mml:mi>μ</mml:mi></mml:mrow><mml:mi>g</mml:mi><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mi>mL</mml:mi></mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>[</mml:mo><mml:mrow><mml:mrow><mml:mi>TC</mml:mi></mml:mrow></mml:mrow><mml:mo>]</mml:mo><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mo>≈</mml:mo><mml:mn>50</mml:mn><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mi>ng</mml:mi><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mi>mL</mml:mi></mml:math> after <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>40</mml:mn><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mi>h</mml:mi></mml:math>, corresponding to a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>></mml:mo><mml:mn>99</mml:mn><mml:mrow><mml:mi>&percnt</mml:mi><mml:mspace></mml:mspace><mml:mspace></mml:mspace></mml:mrow></mml:math> removal. Control (blank) PAN fibres showed only a slow adsorption/degradation rate of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>≈</mml:mo><mml:mn>8</mml:mn><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mi>ng</mml:mi><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mi>mL</mml:mi><mml:mo>⋅</mml:mo><mml:mi>h</mml:mi></mml:math>. The degradation kinetics displayed three regimes: an induction time (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>∼</mml:mo><mml:mn>5</mml:mn><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mi>h</mml:mi></mml:math>), followed by accelerated degradation and late-time deactivation. A heterogeneous dynamic kinetic model (DKM) was used to describe the degradation mechanism, incorporating reactive oxygen species (ROS) generation, catalyst surface inactivation, and polymer stripping effects. The application of an alternating magnetic field (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow><mml:mn>0</mml:mn></mml:msub><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mo>=</mml:mo><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mn>32</mml:mn><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mi>kA</mml:mi><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mspace></mml:mspace><mml:mspace></mml:mspace><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mi>f</mml:mi><mml:mspace></mml:mspace><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mo>=</mml:mo><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mn>450</mml:mn><mml:mrow><mml:mspace></mml:mspace></mml:mrow><mml:mi>kHz</mml:mi></mml:math>) shortened the induction period from several hours to minutes, through the local heating of the MNFs (up to ≈51 °C). For a concentrated pig-manure filtrate (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>[</mml:mo><mml:mrow><mml:mrow><mml:mi>TC</mml:mi></mml:mrow></mml:mrow><mml:msub><mml:mo>]</mml:mo><mml:mn>0</mml:mn></mml:msub><mml:mo>≈</mml:mo><mml:mn>0.32</mml:mn><mml:mrow><mml:mi>μ</mml:mi></mml:mrow><mml:mi>g</mml:mi><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mi>mL</mml:mi></mml:math>), circulation through MNFs with H₂O₂ resulted in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>≈</mml:mo><mml:mn>50</mml:mn><mml:mrow><mml:mi>&percnt</mml:mi><mml:mspace></mml:mspace><mml:mspace></mml:mspace></mml:mrow></mml:math> TC removal. We propose that the degradation process was driven by hydroxyl radical (•OH) formation through hydrogen peroxide (H₂O₂) activation on the MNPs surface. The magnetically triggerable Mn₂FeO₄@PAN nanofibers show that heterogeneous Fenton catalysis can be synergistically combined with localized magnetic heating to accelerate antibiotic degradation, offering a scalable, reusable and efficient alternative for antibiotic-contaminated wastewater with reduced iron sludge versus conventional homogeneous Fenton process..