S. Liu, M. Ahsani, K. Fischer, A. Schulze, A.I. Schäfer 
Photocatalytic removal of steroid hormone micropollutants under simulated sunlight using TiO₂-coated electrospun nanofibers on poly(vinylidene fluoride) membrane 
Sep. Purf. Technol. (2025),  https://doi.org/10.1016/j.seppur.2025.134589  

Solar-driven membrane photocatalysis holds promise for micropollutant removal. TiO₂ is an environmentally benign and abundant semiconductor, but its limited light-harvesting capacity in the visible light region poses a challenge to its application as an effective photocatalyst. Herein, the degradation of steroid hormone (SH) micropollutants was investigated using TiO₂ nanoparticles immobilized on a poly(vinylidene fluoride) microfiltration membrane (TiO₂-PVDF) under simulated solar light (350–1150 nm) at environmentally relevant micropollutant concentrations (100 ng/L estradiol, E2). Key rate-limiting factors influencing SH removal were identified under various operational conditions. The results demonstrated that photon availability was the primary limiting factor for E2 degradation at light intensities below 40 mW/cm². As the light intensity increased, the catalyst surface area (or catalyst loading) accessible to the light became the main constraint. The TiO₂ surface area was thus increased by spinning PVDF nanofibers of varying thickness onto the membrane substrate to enhance the surface area available for TiO₂ loading. A thicker nanofiber layer provided more surface area for TiO₂ attachment (from 0.11 ± 0.01 to 0.33 ± 0.02 mg/cm² as the thickness increased from 70 to 149 µm). However, this improvement came at the expense of light transmission, which decreased substantially from 55 to 19%. Increasing the nanofiber mat thickness from 70 to 149 µm did not significantly enhance the mass removed (from 18 ± 3 to 22 ± 2 ng/cm²), attributed to the reduced light transmission counterbalancing the benefits of increased TiO₂ loading. Amplifying the light irradiance achieved limited enhancement in E2 removal, due to the reduced collision frequency between reactants within the enlarged pores of the nanofiber mat. These findings highlight the importance of striking innovative photocatalytic membrane design that achieves a balance between maximizing catalyst loading and preserving sufficient light penetration, while avoiding excessive pore enlargement. Such an approach is essential for improving the efficiency of micropollutant treatment in membrane photocatalysis.

S. Lotfi, K. Fischer, A. Schulze, A I. Schäfer 
Photocatalytic degradation of steroid hormone micropollutants by TiO₂-coated polyethersulfone membranes in a continuous flow-through process 
Nat. Nanotechnol. (2022),  https://doi.org/10.1038/s41565-022-01074-8  

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).    

K. Fischer, J. Lohmann, E. Schmidt, T. H. Blaich, C. Belz, I. Thomas, et al. 
Anti-biofouling membranes via hydrogel electron beam modification – a fundamental and applied study 
Colloids Surf. A: Physicochem. Eng. Asp. (2023), https://doi.org/10.1016/j.colsurfa.2023.132044  

Biofouling is still a major challenge in membrane science and accounts for up to 70% of the total costs of membrane-operated filtration systems. Thus, in this work, a thin layer of diverse synthetic hydrogels has been applied via electron beam-initiated polymerization on a polyethylene terephthalate (PET) track-etched membrane (fundamental study) as a simple model membrane and on a conventional used polyethersulfone (PES) ultrafiltration membrane (applied study) to study its anti-biofouling properties. The effect of hydrophilicity, roughness, surface charge, and degree of swelling of the attached hydrogel on algae (Chlorella Vulgaris) fouling was studied in a fundamental way, and long-time tests in a membrane bioreactor (MBR, filtration area 1.5 m²) over 11 months were performed on an applied scale. The hydrophilicity, roughness, and surface charge had only a minor to no effect on algae fouling. Only the degree of swelling had an impact on biofouling. The membranes with hydrogels with a low degree of swelling (6%) showed a lower loss of permeability (only 5%) after fouling, compared to a 25% loss with the highest degree of swelling (25%). During the operation over 11 months in a membrane bioreactor (MBR), the permeability is higher (ca. 10%) in a module equipped with hydrogel modified membranes, compared to a module with reference membranes. Thus, modification of membranes with a thin layer of a hydrogel results in an anti-biofouling surface. The degree of swelling is a decisive parameter to control biofouling.  

S. Liu, E. Véron, S. Lotfi, K. Fischer, A. Schulze, A. Schäfer 
Poly(vinylidene fluoride) membrane with immobilized TiO₂ for degradation of steroid hormone micropollutants in a photocatalytic membrane reactor 
J. Hazard. Mater. (2023),  https://doi.org/10.1016/j.jhazmat.2023.130832  

The lack of effective technologies to remove steroid hormones (SHs) from aquatic systems is a critical issue for both environment and public health. The performance of a flow-through photocatalytic membrane reactor (PMR) with TiO₂ immobilized on a photostable poly(vinylidene fluoride) membrane (PVDF-TiO₂) was evaluated in the context of SHs degradation at concentrations from 0.05 to 1000 µg/L under UV exposure (365 nm). A comprehensive investigation into the membrane preparation approach, including varying the surface Ti content and distribution, and membrane pore size, was conducted to gain insights on the rate-limiting steps for the SHs degradation. Increasing surface Ti content from 4% to 6.5% enhanced the 17β-estradiol (E2) degradation from 46 ± 12–81 ± 6%. Apparent degradation kinetics were independent of both TiO₂ homogeneity and membrane pore size (0.1–0.45 µm). With optimized conditions, E2 removal was higher than 96 % at environmentally relevant feed concentration (100 ng/L), a flux of 60 L/m²h, 25 mW/cm², and 6.5% Ti. These results indicated that the E2 degradation on the PVDF-TiO₂ membrane was limited by the catalyst content and light penetration depth. Further exploration of novel TiO₂ immobilization approach that can offer a larger catalyst content and light penetration is required to improve the micropollutant removal efficiency in PMR. 

K. Fischer, A. Abdul Latif, J. Griebel, A. Prager, O. Shayestehpour, S. Zahn, A. Schulze 
Immobilization of Bi₂WO₆ on polymer membranes for photocatalytic removal of micropollutants from water – a stable and visible light active alternative  
Global Challenges (2024),  https://doi.org/10.1016/j.jhazmat.2023.130832  

In this work, bismuth tungstate Bi₂WO₆ is immobilized on polymer membranes to photocatalytically remove micropollutants from water as an alternative to titanium dioxide TiO₂. A synthesis method for Bi₂WO₆ preparation and its immobilization on a polymer membrane is developed. Bi₂WO₆ is characterized using X-ray diffraction and UV–vis reflectance spectroscopy, while the membrane undergoes analysis through scanning electron microscopy, X-ray photoelectron spectroscopy, and degradation experiments. The density of states calculations for TiO₂ and Bi₂WO₆, along with PVDF reactions with potential reactive species, are investigated by density functional theory. The generation of hydroxyl radicals ^•OH is investigated via the reaction of coumarin to umbelliferone via fluorescence probe detection and electron paramagnetic resonance. Increasing reactant concentration enhances Bi₂WO₆ crystallinity. Under UV light at pH 7 and 11, the Bi₂WO₆ membrane completely degrades propranolol in 3 and 1 h, respectively, remaining stable and reusable for over 10 cycles (30 h). Active under visible light with a bandgap of 2.91 eV, the Bi₂WO₆ membrane demonstrates superior stability compared to a TiO₂ membrane during a 7-day exposure to UV light as Bi₂WO₆ does not generate ^•OH radicals. The Bi₂WO₆ membrane is an alternative for water pollutant degradation due to its visible light activity and long-term stability. 

• Upscaling – From Fundamentals to Application 
• Photocatalysis (Degradation in different reactors – batch, continuous: over stream, cross-flow, dead-end) 
• Adsorption (batch, continuous: over stream, cross-flow, dead-end) 
• Enzymes (Hydrolases such as lipases, proteases and amylases, oxidoreductases such as laccase)
• Characterization of the degradation of various pollutants (diclofenac, ibuprofen, ranitidine, propanolol, aspartame, acesulfame K, cimetidine, ofloxacin, sulfomethoxazole, glyphosate

• Analytics: 

  • Permeance (dead-end, cross-flow) 
  • Bubble point, MWCO, sieve  curve analysis, Hg porosimetry, porometry 
  • Contact angle, surface energy 
  • Zeta potential, surface charge density 
  • Protein adsorption (BCA test) 
  • Fouling (proteins, algae, wastewater, surface water, etc.) 
  • Toxicity (luminescent bacteria) 
  • Enzyme activities (various enzymes) 
  • Photocatalytic activity (static and continuous operating modes) 
  • Adsorption of micropollutants 
  • SEM, TEM, AFM 
  • Tensile test, DMA 
  • TOC, ICP-OES, SPME-GC/MS 
  • IR, Raman, UV/VIS 
  • XPS, XRD, EDX