Degradação fotocatalítica de antibióticos sulfonamidas empregando nitreto de carbono grafítico (g-C3N4) e g-C3N4/Fe3O4 magneticamente recuperável”

Abstract

The presence of sulfonamide antibiotics in aquatic environments represents a significant environmental concern due to their persistence and potential to promote the spread of bacterial resistance. In this work, two visible-light-active photocatalysts were synthesized: graphitic carbon nitride (g-C₃N₄), obtained by urea pyrolysis, and the magnetic composite 3% Fe₃O₄/gC₃N₄, prepared from melamine through a combined pyrolysis and solvothermal route. The materials were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), UV–Vis Diffuse Reflectance Spectroscopy (DRS), textural analysis (BETBJH), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS). FTIR spectra of g-C₃N₄ showed bands between 1200–1650 cm⁻¹ associated with C–N and C=N vibrations of the heptazine framework and a band at ~799 cm⁻¹, characteristic of triazine/heptazine ring breathing modes. In the g-C₃N₄ / Fe₃O₄ (3%) composite, an additional absorption at ~586 cm⁻¹ corresponding to the Fe–O stretching vibration confirmed the incorporation of magnetite. XRD patterns revealed characteristic peaks of g-C₃N₄ at 2θ ≈ 13° (100) and 27° (002), while Fe₃O₄ exhibited reflections of the cubic spinel structure at 18.3° (111), 30.1° (220), 35.6° (311), 43.3° (400), 53.5° (422), 57.3° (511) and 62.9° (440), consistent with PDF 01-075-0449. The composite showed the coexistence of both phases. DRS analysis indicated a band gap of ~2.8 eV for g-C₃N₄. Morphological analysis revealed a sponge-like structure for g-C₃N₄, while the composite exhibited structural stability and magnetic recoverability. Photocatalytic tests showed that g-C₃N₄ outperformed photolysis, achieving degradation efficiencies of 94% for sulfathiazole (k = 7.8 × 10⁻³ min⁻¹), 77% for sulfadiazine (k = 8.8 × 10⁻³ min⁻¹), and 72% for sulfapyridine (k = 6.9 × 10⁻³ min⁻¹), maintaining stability over six reuse cycles. The 3% Fe₃O₄/g-C₃N₄ composite achieved 80% sulfathiazole degradation (k = 1.4 × 10⁻² min⁻¹) within 100 min, showing stability over four cycles and the advantage of magnetic separation. Mechanistic studies indicated that photogenerated holes (h⁺) were the dominant reactive species, followed by superoxide radicals (O₂•⁻) and hydroxyl radicals (•OH). These results highlight the high photocatalytic efficiency of urea-derived g-C₃N₄, while the magnetic composite offers operational advantages related to catalyst recovery and reuse, demonstrating strong potential for advanced oxidation processes aimed at the removal of antibiotics from aqueous systems.