Hydrothermal Modification of Zinc Oxide and Titanium Dioxide for Photocatalytic Degradation of Rhodamine B

Zinc oxide (ZnO) and titanium dioxide (TiO2) powders were hydrothermally modified in 10 M sodium hydroxide solutions at 120 degrees C for 24 hours to alter its morphologies. Hydrothermally treated ZnO and TiO2 showed partially rod-shaped particles and used as catalysts in the photocatalytic degradation of Rhodamine B under UV illumination. The effect of operational parameters on degradation efficiency such as catalyst loading (0.5 g/L to 2.5 g/L), initial dye concentration (2.5 ppm to 12.5 ppm), initial H2O2 concentration (0.1 M to 4.0 M) and solution pH (3 to 11) were studied. ZnO showed better photocatalytic activity as compared to TiO2 because ZnO has a lower bandgap energy and more active electron-hole pairs formation in the system. The optimum conditions were 0.5 M H2O2, 1.5 g/L ZnO suspension and 7.5 ppm Rhodamine B at neutral solution pH. The degradation of Rhodamine B followed pseudo first order reaction, with the apparent rate of reaction, k(app) = 0.0501 min(-1). An effective, efficient and environmental friendly method to remove organic dye from wastewater was developed and could be implemented in treating various types of organic pollutants.