Fig. 6. Photocatalytic degradation of MB by the as-prepared samples alone (a), or the catalysts in conjunction with H₂O₂ (b) under visible-light irradiation. Unless otherwise stated, the reaction conditions are: [MB] = 10 mg L⁻¹, 60 mL MB solution, [catalyst] = 1 mg mL⁻¹, visible light irradiation (λ > 420 nm, 500 W), T = 25 °C, initial pH = 6.4. (c) Effect of solution pH on the zeta potentials of CoFe₂O₄ and CoFe₂O₄–RGO hybrids. (d) MB degradation using CoFe₂O₄–RGO/H₂O₂: effect of hydrogen peroxide dose (reaction conditions: [MB] = 10 mg L⁻¹, 60 mL MB solution, [catalyst] = 1 mg mL⁻¹).