2.3. Bleached DFF

The extracted DFF samples were soaked with 3% NaOH (1:10, w/v) at 120 °C for 15 min in an autoclave, then filtered and washed with hot distilled water several times. This step was repeated until the filtrated solution remained colorless. Afterward, the remaining solid was neutralized by washing with distilled water until pH ~7. The sample was then air dried overnight and stored for the next steps. The DFF sample was bleached in an aqueous solution containing H₂O₂ (1.3%, w/w) and acetic acid (0.1%, v/v) (this solution was prepared by combining 74 mL 35% w/w H₂O₂ in H₂O with 2 L H₂O and adding 2 mL of glacial acetic acid) by stirring at 70 °C for 2 h. The solids were filtered off and washed with H₂O (3 × 500 mL). This bleaching/washing cycle was repeated once. After two cycles, the solids were washed with H₂O until the pH was neutral and dried for 24 h at ambient temperature and pressure.