Fig. 3. (a) Scanning electron microscope (SEM) image of oxide-free (dithionite–citrate-treated) Prassa-Kimolos bentonite (Greece), (b) oxide-free bentonite treated with 30% (wt/wt) H₂O₂ (6 h, 80°C) in the presence of 230 mg L^–1 dissolved organic C. Bars represent 100 µm.