Kinetics of MB degradation and effect of pH on the photocatalytic activity of MIn2O4 (M = Ca, Sr, Ba) under visible light irradiation

Degradation of Methylene Blue (MB) on MIn2O4 (M = Ca, Sr, Ba) semiconductors was observed and the analysis of the products confirmed that MB was decomposed other than simply bleached on these photocatalysts under visible light irradiation. The activity order under visible light irradiation was CaIn2O4 > SrIn2O4 > BaIn2O4. The reaction kinetics of MB degradation on MIn2O4 was investigated, suggesting that these reactions followed approximately first-order kinetics. Furthermore, the effects of pH value of the solution on the photocatalytic properties of these materials were observed in detail, which indicated that the decomposition efficiency of MB was the highest in the alkaline solution and the lowest in the acidic solution on all of the photocatalysts.