Degradation of ibuprofen in the carbon dots/Fe3O4@carbon sphere pomegranate-like composites activated persulfate system

Abstract

Carbon dots and nanomagnetites encapsulated in amorphous carbon spheres (CDs/Fe3O4@CS) with a pomegranate-like structure were synthesized via a solvothermal method and their peroxide activation performances for ibuprofen degradation were investigated in this work. The pomegranate-like nanocomposites, with an average diameter of 451.9 nm, possessed multicores and a 20–50 nm thick amorphous carbon shell. The multicores were composed of multiple 3.9–9.8 nm carbon dots and 5.6–18.6 nm nanomagnetites, as confirmed by X-ray diffraction, X-ray photoelectron, Raman and photoluminescence spectra. The Fe3O4 loading was calculated to be 50.9 wt% according to thermo-gravimetric analysis. CDs/Fe3O4@CS had a specific surface area of 101.5 m2/g and the saturation magnetization of 26.8 emu/g. The CDs/Fe3O4@CS formation mechanism was proposed based on the characterization results. CDs/Fe3O4@CS exhibited high catalytic activities for peroxymonosulfate, persulfate and H2O2 with and without visible light illumination, and persulfate showed higher ibuprofen degradation efficiencies. The amorphous carbon shell might benefit ibuprofen enrichment, the nano Fe3O4 provided sufficient reactive sites to activate persulfate, and the CDs could accelerate the degradation due to their excellent electron donating and accepting abilities. The ibuprofen degradation in the CDs/Fe3O4@CS activated persulfate system followed a pseudo-first-order kinetic model and the activation energy was derived as 27.2 kJ/mol. The CDs/Fe3O4@CS also presented good reusability performances in the repeated experiments with visible light illumination. Singlet oxygen, hydroxyl and sulfate radicals were verified and the roles of these reactive species in ibuprofen degradation pathways were discussed based on intermediate analysis. The pomegranate-like nanocomposites might provide a potential promising catalyst for pollution control technologies.