M. Schmidt, D. Breite, I. Thomas, M. Went, A. Prager, A. Schulze
J. Membr. Sci. 563 (2018) 481-491
https://doi.org/10.1016/j.memsci.2018.06.013

Immobilization of different digestive enzymes consisting of proteases, amylases and lipases on polyvinylidene fluoride resulted in biocatalytic active polymer membranes with self-cleaning capability. Activation of enzymes and therefore “switching on” the membrane system was achieved by adjusting pH and temperature leading to an active degradation of fouled substances on its surface. Fouling and self-cleaning experiments with solutions of protein, lipid, carbohydrate, and a mixture were performed and resulted in high recovery of water permeance (99%, 72%, 77%, and 68%, respectively). Furthermore, real samples including river water (75% after first cycle), and household sewage (62%) were examined, as well as first investigations in longtime performance, and stability were performed. Comprehensive membrane characterization was conducted by investigation of the immobilized enzyme concentration, enzyme activity, fouling tests and water permeation monitoring, mercury porosimetry, X-ray photoelectron spectroscopy, scanning electron microscopy, and finally, zeta potential, as well as water contact angle measurements.

M. Schmidt, S. Zahn, F. Gehlhaar, A. Prager, J. Griebel, A. Kahnt, et al.
Polymers2021, 13(11), 1849
https://doi.org/10.3390/polym13111849

Radiation-induced graft immobilization (RIGI) is a novel method for the covalent binding of substances on polymeric materials without the use of additional chemicals. In contrast to the well-known radiation-induced graft polymerization (RIGP), RIGI can use non-vinyl compounds such as small and large functional molecules, hydrophilic polymers, or even enzymes. In a one-step electron-beam-based process, immobilization can be performed in a clean, fast, and continuous operation mode, as required for industrial applications. This study proposes a reaction mechanism using polyvinylidene fluoride (PVDF) and two small model molecules, glycine and taurine, in aqueous solution. Covalent coupling of single molecules is achieved by radical recombination and alkene addition reactions, with water radiolysis playing a crucial role in the formation of reactive solute species. Hydroxyl radicals contribute mainly to the immobilization, while solvated electrons and hydrogen radicals play a minor role. Release of fluoride is mainly induced by direct ionization of the polymer and supported by water. Hydrophobic chains attached to cations appear to enhance the covalent attachment of solutes to the polymer surface. Computational work is complemented by experimental studies, including X-ray photoelectron spectroscopy (XPS) and fluoride high-performance ion chromatography (HPIC).

R. Das, P. Solís-Fernández, D. Breite, A. Prager, A. Lotnyk, A. Schulze, H. Ago
Chem. Eng. J. 420 (2021) 127721
https://doi.org/10.1016/j.cej.2020.127721

Water pollution has prejudicial effects on human health and ecosystems. An advanced membrane technology, which uses less energy for pollutants removal from water, is strongly desired for improving cost efficiency. This study demonstrates a high-flux enabled non-functionalized hexagonal boron nitride (h-BN) lamellar membrane, which retains pollutants through adsorption mediated filtration system–a phenomenon that is not yet studied. The membrane is found to be pH responsive, and acidic solution increases anionic methyl orange (MO) and direct red-80 (DR-80) dyes retention up to ≥90%. It also improves permeance fluxes by ~15 and 61-folds for MO and DR-80, respectively, as compared with the previous studies. Next, the membrane qualifies to be a good adsorbent for pollutants removal. The maximum adsorption capacities of this h-BN membrane for bisphenol A, MO and DR-80 are 125.7, 120.8, and 328.2 mg g−1, respectively. Furthermore, the anti-fouling performance of the membrane has been studied. The membrane exhibits normal fouling tendency, but could be recovered to 80% after washing. The membrane is very stable, and no swelling is observed even in extremely high acidic and basic conditions. The membrane could be regenerated with ethanol treatment and retained dye removal efficiency (around 90%) after four consecutive cycles test.

S. Lotfi, K. Fischer, A. Schulze, A. I. Schäfer
Nat. Nanotechnol. 17 (2022) 417-423
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).