**2. Experimental**

#### *2.1. Materials for Membranes Preparation*

Poly(ethylene oxide) (PEO, Mw=4M ≈ 4 × 10<sup>6</sup> g/mol) and Silica (Nanopowder, average size = 10–20 nm—"BET" Brunauer–Emmett–Teller) were purchased form Sigma-Aldrich (St. Louis, MO, USA). Bi-distilled water was produced in house.

#### *2.2. Membrane Separators Fabrication*

An in-house made electrospinning apparatus, composed of a high voltage power supply (Spellman SL 50 P 10/CE/230, Hauppauge, NY, USA), a syringe pump (KD Scientific 200 series, Holliston, MA, USA), a glass syringe, a stainless steel blunt-ended needle (inner diameter: 0.84 mm) connected with the power supply electrode, and a grounded aluminum plate-type collector (area ≈10 cm2), was utilized in order to prepare the electrospun PEO membranes. The water-based PEO polymer solution was dispensed through a Teflon tube to the needle that was vertically placed on the collecting plate. PEO was dissolved at a concentration of 3% w/v in bi-distilled water. To create the composite systems, after the polymer dissolution, silica nanoparticles were added to the resulting solutions in proper amounts in order to produce a final membrane containing 10% w/w of silica. The realized dispersions were electrospun by using the following conditions: voltage = 13 kV, needle-to-collector distance = 30 cm, and flow rate = 0.005 mL/min. A quality control was performed in order to verify the homogeneity of the sample thickness by means of a digital micrometer. Only specimens having thicknesses in the range of 50 ± 10 μm were used for further characterizations.

The two synthesized membranes will be here labelled as "es-PEO" (for the electrospun sample based on pure PEO) and "es-PEO-SiO2" (for the electrospun sample based on PEO with 10% of silica particles)
