Polyvinyl alcohol (PVA, Mowiol 18-88) and silicotungstic acid hydrate H4SiW12O40 (HSiW, purum) were purchased from Merck and used as received. Deionized water was used as a solvent. For electrospinning, a Nanospider NS LAB500S instrument (Elmarco, Czech Republic) equipped with a cylindrical electrode with micro blades for allocation of the electrical charge and solution droplets was used (shown schematically in Figure ). Electrospinning preparation of green composite fibers consisting of PVA and HSiW was described in a previous study. The experimental procedure used here is described in Supplementary Experimental