Efficient degradation of tetracycline contaminants by a flow-through Electro-Fenton system: Carbon nanotube-encapsulated α-Fe2O3 under nanoconfinement

Developing nano-space confined materials for efficient tetracycline removal is still a challenge. In this study, the catalytic membrane cathode (alpha-Fe2O3@CNT) with a nanoconfinement effect was synthesized by encapsulating alpha-Fe2O3 into the carbon nanotube (CNT) pores. Most of the alpha-Fe2O3 was encapsulated into the inner wall of the CNTs in the form of nanoparticles (NPs) and was highly dispersed, which enabled the catalytic membrane cathode to have good contact efficiency with active sites for pollutants and promoted the degradation efficiency of tetracycline. When combined with the response surface method, 94.7 % of tetracycline could be degraded in 60 min under the most favorable process parameters ([Na2SO4]0 = 0.052 mol center dot L- 1, current intensity = 2.46 mA center dot cm- 2, pH = 6.73, and [tetracycline]0 = 10 mg center dot L- 1). After 8 consecutive cycles of degradation, the alpha-Fe2O3@CNT catalytic membrane cathode still maintained a stable tetracycline removal rate. In addition, the average electron transfer number of the electrode was 2-2.3, and the selectivity for 2e- oxygen reduction reaction was more than 90 %, which indicated a significant selectivity for 2e- oxygen reduction. Meanwhile, under the synergistic effect of CNT nanoconfinement and alpha-Fe2O3 NPs, more active species (center dot OH and 1O2) were generated, which accelerated the removal of tetracycline. This study presented an innovative strategy for the environmentally friendly and energy efficient degradation of tetracycline.