Photo-Activated ClO2 • Oxidation of PP NWFs. The PP NWFs (40-50 mg; 4 × 4 cm 2 ) were oxidized by the ClO2 • gas generated from an aqueous solution (20 mL) of NaClO2 (200 mg) and 35% HCl aq. (100 μL), under irradiation with a 60 W LED lamp (λ = 365 nm, 5 mW/cm 2 ). A glassware system reported previously was used to perform the oxidation of a PP NWF in a large size and/or under heating conditions. An aqueous solution of NaClO2 was added to the outer moat of the glassware, while the sample was placed on the inner side. During the reaction, the sample was protected from direct UV irradiation using aluminum sheet. The reaction was carried out in three stages at 30 °C, 60 °C, and 80 °C. The oxidized samples were labeled Ox-30, Ox-60, and Ox-80, respectively.