Carbon nanotube membrane armed with confined iron for peroxymonosulfate activation towards efficient tetracycline removal

The water treatment performance of metal-based peroxymonosulfate (PMS) catalytic membrane is always limited by the finite residence time and complex water matrixes. Therefore, the development of high efficiency and anti-interference PMS catalytic membrane is of great significance. In this work, an oxidized carbon nanotube membrane with Fe2O3 nanoparticle confined inside (Fe2O3@OCNT) has been fabricated for enhanced PMS activation in the membrane filtration process (MFPA process). The experiment results showed that through fine-tuning the confinement degree of Fe2O3 in OCNT, the non-radical electron transfer pathway was gradually enhanced and became the dominant process. Under the suitable confinement condition, the tetracycline (TC) removal in the Fe2O3@OCNT MFPA process was up to 96.1 % with a residence time of only 8.0 s, which remarkably outperformed the powder-based or batch process. The high efficiency of the membrane was attributed to the enhanced mass transfer and non-radical electron transfer process due to the nanoconfinement effect. This was supported by theoretical calculations, where it was showed that confining Fe2O3 inside OCNT not only enhanced the electron activity in the lumen of OCNT, but also increased the adsorption energy for PMS. In addition, the four possible degradation pathways of TC were proposed based on Fukui function analysis and LC-MS results. This system displayed reusability and good stability for TC removal (5 cycles > 85 %, low Fe leaching of 10 μg·L-1, and long-term running of 48 h) and wide applicability for different pollutants, while also demonstrated unique anti-interference property in the presence of inorganic ions and in real water matrixes.