Electrospinning composite nanofibers of wool keratin with nanoparticles from water solutions

Keratin extracted from wool can be solubilised in formic acid to produce nanofibers by electrospinning [1]. This protein (thanks to its active sites) has properties to remove toxic substances such as formaldehyde [2], metal ions [2] and dyes [3]. In addition, it becomes insoluble in water when treated at high temperature [4] to permit use in filtration of water and wet gas streams. In this work, to avoid the use of organic solvents (e.g. formic acid), solutions of keratin in water were doped with inorganic nanoparticles (Ag or TiO2 water nanosol) and they were successively electrospun into nanofibrous membranes, by adding poly(ethylene oxide). The as-spun keratin/PEO/nanoparticles nanofibers showed a highly interconnected fibrous structure of beaded nanofibers. Moreover, heat treatments were successfully applied to electrospun nanofibers to produce water insoluble keratin-based membranes in spite of the presence of PEO. In this way, it was also possible to remove PEO from the nanofibers increasing the keratin content and maintaining a nanofibrous structure and small-sized porosity comparable to the as-spun materials. Antibacterial and photocatalytic properties of the nanofibres doped with Ag or TiO2 nanoparticles were tested. Antibacterial tests against Escherichia coli were carried out using AATCC 100 Test Method. Both composite nanofibers showed excellent antibacterial properties, with bacteria reduction of 95% for Ag and 97% for TiO2, as sign that the nanoparticles can exert their functions even if embedded in keratin nanofibers. Furthermore, the photocatalytic test based on model reaction of Rhodamine B dye degradation showed promising photocatalytic properties for the hybrid electrospun nanofibers. Indeed the result in term of conversion was 53% for TiO2-loaded nanofibres in 2 h under 9 W/m2 UV light. Nevertheless, the conversion is not complete, it evidences a considerable activity improvement with respect to the data resulting from the electrospun sample without TiO2 nanoparticles, which shows the same activity of the solution alone.