Lanthanide oxide doped zinc oxide: effective photocatalysts for the degradation of diesel in seawater under visible light irradiation

Nanocrystalline lanthanide oxide doped ZnO has been prepared by a simple and efficient technique for exhibiting an enhanced visible light photocatalytic activity. The prepared photocatalysts were characterized by SEM, XRD and UV-Vis DRS analysis. XRD data showed that the particles of samples were highly nanosized and crystalline. The sizes of Yb2O3/ZnO, Er2O3/ZnO and Pr6O11/ZnO nanoparticle were 40.97, 40.94 and 51.18 nm and found to be mixed morphology. Six factors such as dosage of photocatalysts, coupling ratio of lanthanide oxide and ZnO, initial concentration of diesel, concentration of H2O2, illumination time of visible light and pH value were changed in order to test the photocatalytic activity and efficiency of reaction. The enhanced photocatalytic activity was due to the presence of f shells in the lanthanide oxide crystal lattice which delays the process of recombination of electron hole pair. According to the results, diesel removal was < 30% without any catalyst (losses only by evaporation) and the optimized effects of Yb2O3/ZnO, Er2O3/ZnO and Pr6O11/ZnO occurred when the catalyst dose at 0.4, 0.6 and 0.4 g/L, catalyst-coupling ratio at 40, 30 and 10%, initial diesel concentration was 0.05, 0.10 and 0.20 g/L, H2O2 concentration at 4, 4 and 6 mg/L, illumination time at 1.5, 1.5, 2.5 h and pH at 7, 10 and 6 respectively, in which case the diesel removal rate reached 95.48, 98.60 and 90.81%. The experimental results clearly show that lanthanide oxide doped nanocrystalline semiconductor are highly active under visible light irradiation and may find wider applications in environmental remediation technologies.