Enhanced tetracycline degradation using carbonized PEI-grafted lignin microspheres supported Fe-loading catalyst...

Traditional homogeneous Fenton systems face limitations, including a narrow pH range, potential secondary pollution, and poor repeatability. In this study, these bottlenecks in tetracycline wastewater treatment were addressed with using carbonized porous polyethyleneimine-grafted lignin microspheres (PLMs) supported Fe-loading catalysts (PLMs/Fe-C). An optimized PLMs/Fe-C catalyst under specific conditions (carbonization temperature: 350 °C, PLMs: Fe = 1:1, and alkali lignin: PEI = 1:4) was developed, which proved to be an efficient Fenton-like catalyst for tetracycline (TC) degradation. TC degradation results showed that the PLMs/Fe-C + H₂O₂ system achieved a high removal efficiency of 100 % within 150 min (50 mL TC with an initial concentration of 50 mg/L, 0.015 g catalyst, 0.5 mL H₂O₂), demonstrating its applicability over a wide pH range (3-10) and the capability to remove multiple pollutants (2,4-D, BPA, Lev, etc.). This efficiency was attributed to the stronger electron-donating ability and mass transfer properties derived from the porous structure and functional groups. Arrhenius fitting analysis revealed a lower activation energy (E = 52.98 kJ/mol) for the PLMs/Fe-C, indicating a more accessible reaction. Additionally, the removal efficiency marginally decreased from 100 % to 98.32 % after five cycles, demonstrating excellent reusability. Mechanistic investigations indicated that the PLMs/Fe-C can activate H₂O₂ to produce reactive oxygen species •OH, ¹O₂, effectively degrading TC.