Micropollutants in the aquatic environment pose a high risk to both environmental and human health. The photocatalytic degradation of steroid hormones in a flow-through photocatalytic membrane reactor under UV light (365 nm) at environmentally relevant concentrations (50 ng l–1 to 1 mg l–1) was examined using a polyethersulfone–titanium dioxide (PES–TiO2) membrane. The TiO2 nanoparticles (10–30 nm) were immobilized both on the surface and in the nanopores (220 nm) of the membrane. Water quality and operational parameters were evaluated to elucidate the limiting factors in the degradation of steroid hormones. Flow through the photocatalytic membrane increased contact between the micropollutants and ·OH in the pores. Notably, 80% of both oestradiol and oestrone was removed from a 200 ng l–1 feed (at 25 mW cm–2 and 300 l m–2 h–1). Progesterone and testosterone removal was lower at 44% and 33%, respectively. Increasing the oestradiol concentration to 1 mg l–1 resulted in 20% removal, whereas with a 100 ng l–1 solution, a maximum removal of 94% was achieved at 44 mW cm–2 and 60 l m–2 h–1. The effectiveness of the relatively well-known PES–TiO2 membrane for micropollutant removal has been demonstrated; this effectiveness is due to the nanoscale size of the membrane, which provides a high surface area and facilitates close contact of the radicals with the very small (0.8 nm) micropollutant at an extremely low, environmentally relevant concentration (100 ng l–1).
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The Helmholtz Association is thanked for Recruitment Initiative funding, as well as the Helmholtz ERC Recognition Award NAMEPORED to A.I.S. Deutscher Akademischer Austauschdienst (DAAD) provided a PhD stipend to S.L. H. Lambach and S. Schweikert-Joß (IMVT-KIT) are thanked for the fabrication of the photocatalytic membrane cell. At IMT-KIT, B. S. Richards contributed helpful discussions on light data analysis and T. Berger provided support in micro-cross-flow system troubleshooting, LabVIEW programming and light absorption measurements. At Leibniz-IOM, A. Prager supplied SEM images and A. A. Latif performed the TiO2 coating of membranes. T. Luxbacher (Anton Paar) and J. Lützenkirchen (INE-KIT) contributed expertise with streaming potential measurements. At IAMT, R. Lyubimenko developed the UHPLC analysis, assisted with operation and contributed to discussion of calculation methods, C. Regmi prepared membrane cross-sections, J. C. Espíndola discussed aspects of data interpretation, A. Imbrogno established the error calculation methodology, M. Nguyen supported with LabVIEW operation, IT troubleshooting, provided hormone properties and took care of regraphing and error corrections, E. Véron carried out E2 photocatalytic degradation experiments with the TiO2_120C membrane, and C. Suliani Raota carried out repeat experiments with methylene blue. Last but not least, we express our sincere gratitude to F.-D. Kopinke (UFZ Leipzig) for his post-acceptance review that helped identify errors and significantly improve the manuscript.
The authors declare no competing interests.
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Lotfi, S., Fischer, K., Schulze, A. et al. Photocatalytic degradation of steroid hormone micropollutants by TiO2-coated polyethersulfone membranes in a continuous flow-through process. Nat. Nanotechnol. 17, 417–423 (2022). https://doi.org/10.1038/s41565-022-01074-8
Nature Nanotechnology (2022)