Encapsulation of Fe⁰-dominated Fe₃O₄/Fe⁰/Fe₃C nanoparticles into carbonized polydopamine nanospheres for catalytic degradation of tetracycline via persulfate activation

Porous carbonized polydopamine nanospheres encapsulated with Fe⁰-dominated Fe₃O₄/Fe⁰/Fe₃C nanoparticles (Fe@C-PDA) were feasibly fabricated by a one-step pyrolysis of the Fe-PDA polymer, which was employed to activate persulfate (PS) toward degrading tetracycline (TC). The morphology, structure, chemical compositions and textural properties of the resulting catalyst were characterized systematically, and effects of catalyst dosages, PS concentration, inorganic anions (HCO₃⁻ and Cl⁻), natural organic matter and practical water body were studied in detail. The N-doping derived from C-PDA not only enhanced TC adsorption capacity, but also worked as active sites for PS excitation. Moreover, Fe@C-PDA displayed an excellent efficiency and stability in the 5th cycle tests. Electron paramagnetic resonance, classical radical scavenging experiments and X-ray photoelectron spectroscopy analysis disclosed that the active species in the system were identified as sulfate radicals (SO₄^[rad]−) and hydroxyl radicals (^[rad]OH), and the variable chemical valences of Fe₃O₄/Fe⁰/Fe₃C nanoparticles as well as N-doping in the C-PDA nanospheres contributed to the outstanding catalytic activity. This work can provide new insight of making this kind of Fe-based materials as the promising catalysts for application in eliminating organic pollutants.