CuFe2O4 modified expanded graphite synthesized by urea-assisted hydrothermal method for tetracycline treatment through persulfate activation: Characterization, mechanism and degradation intermediates

Abstract

• Expanded graphite (EG) was applied as the support of CuFe 2 O 4 . • Composite catalyst (EG-CuFe 2 O 4 -U) was synthesized by the urea-assisted hydrothermal method. • EG-CuFe 2 O 4 -U possessed outstanding catalytic performance to PDS activation for TC degradation. • Both SO 4 ·− , ·OH and 1 O 2 were generated in the EG-CuFe 2 O 4 -U/PDS system. • The intermediates of TC were detected and analyzed. Owing to the stable crystal structure and wide range of pH applications, CuFe 2 O 4 particles have been intensively concerned in the field of advanced oxidation, but their serious agglomeration and slow catalytic efficiency are still the stumbling blocks. The composite catalyst (EG-CuFe 2 O 4 -U) prepared by urea-assisted hydrothermal method with expanded graphite (EG) as the substrate immobilized CuFe 2 O 4 not only exposed more active sites but also exhibited a higher electron transfer rate. Additionally, EG-CuFe 2 O 4 -U showed excellent performance in degrading tetracycline (TC) in model wastewater by activated peroxydisulfate (PDS). The synthesis mechanism of EG-CuFe 2 O 4 -U and the principle of urea in the formation of reduction environment were discussed in detail by the experimental results of key preparation parameters and characterization. Meanwhile, several critical influencing factors were examined including PDS concentration, catalyst dosage, initial pH of the solution, and the change of pH in different systems. Furthermore, the removal efficiency and mineralization efficiency of TC (50 ppm) exceed 91% and 34.6%, on the conditions of 0.4 gL −1 EG-CuFe 2 O 4 -U, 6 mM PDS, initial solution pH of 4, and room temperature. What’s more, the internal reaction mechanism of free radicals and non-free radicals in the EG-CuFe 2 O 4 -U/PDS system was further elaborated via scavenging tests, electron paramagnetic resonance (EPR). Finally, based on twenty-one principal intermediates of TC, four possible degradation pathways were proposed. In general, the catalyst with a rich pore structure and high catalytic activity has great potential in the effective activation of PDS and is prospective to be further applied in the field of antibiotic wastewater degradation.