Photodegradation of Methylene Blue Using a UV/H2O2 Irradiation System

Abstract

This study presents an efficient way to degrade methylene blue (MB) present in water via photodegradation using H2O2 as an oxidant in the presence of UV irradiation and without the use of a catalyst. The reaction variables, employed to evaluate the performance of the photodegradation process using the UV/H2O2 system, were the amount of H2O2 in the reacting solution and the initial concentration of methylene blue. The degradation of methylene blue in the presence of H2O2 was not observed during agitation in darkness. The degradation time decreased as the H2O2 concentration increased after the ideal concentration was reached. At this stage, as it began to scavenge the generated hydroxyl radicals, the rate of degradation became inversely proportional to the concentration of H2O2. An increase in the quantities of MB and H2O2 improved the degradation efficiency because the oxidation process was aided by using the appropriate amount of H2O2 and an ideal length of UV light exposure. The experimental data obtained were well-fitted to zero-order reaction kinetics based on the high values of the correlation coefficient. It is believed that the OH radicals (OH●) generated during the breakdown of H2O2 and the generated O2●− species attack the MB molecules and produce MB radicals (MB●). These MB radicals further experience oxidation and convert to intermediates and finally to CO2 and H2O. The UV/H2O2 system proved to be quite efficient for the photodegradation of methylene blue without the use of any solid catalyst. This UV/H2O2 system can be employed in the degradation of other organic pollutants in industrial wastewater.