Kinetic Study of Photocatalytic Degradation of Methylene Blue by Zinc Cadmium Sulfide Particles under UV Irradiation
Abstract
Zinc cadmium sulfide (ZCS) nanoparticles with the Zn2+ : Cd2+ mole ratios of 4 : 1 (ZCS1) and 1 : 4 (ZCS2) were synthesized using microwave irradiation method. Photocatalytic activity of ZCS1 and ZCS2 towards the degradation of methylene blue (MB) in water at room temperature (27±1oC) under UV irradiation was investigated. The effects of parameters such as the initial MB concentration (8 - 12 mg L-1), pH (3 - 6) and catalyst dose (0.06 - 0.12 g L‑1) on the reaction kinetics, MB degradation efficiency under UV irradiation (%DEG) and MB removal efficiency (%REM) were examined. The degradation kinetics of MB followed the first-order kinetic model under all conditions attempted, except for the case of ZCS2 at pH = 3 where the degradation of MB exhibited the zero-order reaction behavior. The rate constant (kobs,1) for the degradation of MB was found to increase with increasing pH, but did not vary much with the initial MB concentration. Based on the values of kobs,1, the photocatalytic activity of ZCS2 (0.0236 min-1 £ kobs,1 £ 0.0283 min-1) was superior to that of ZCS1 (0.0118 min-1 £ kobs,1 £ 0.0212 min-1). The optimal conditions for the MB removal in this work included the initial MB concentration of 12 mg L‑1, pH = 9 and the catalyst dose of 0.1 g L‑1. These conditions essentially leaded to the maximum values of both %DEG (91.5% and 96.0% for ZCS1 and ZCS2, respectively) and %REM (95.4% and 97.3% for ZCS1 and ZCS2, respectively) at the UV irradiation time of 120 minutes.References
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