Fast and Efficient Methylene Blue Photodegradation Process Using Natural Iron Oxide as Catalyst in the Dark and Under Irradiation

Heterogeneous photodegradation of Methylene Blue (MB) in the presence of Natural Iron Oxide (NIO) was investigated in the solution medium. Five methods for characterizing the NIO were employed: X-ray diffraction (XRD), X-ray fluorescence and Brunauer–Emmett–Teller (BET) analysis, Raman andscanning electron microscopy (SEM). These analyses showed that the NIOconsists essentially ofhematite(89 %). To dissolving iron from the NIO we have used citric acid, tartaric and oxalic acid and the results confirmed that the Fe(II) was obtained in the presence of oxalic acid (OA). Under UVA light, the most efficient degradation of MB was achieved with the OA which 100 % degradation ratio was reached within 90 minutes. The effect of various parameters such as concentration of dye, concentration of OA, pH and type of radiation (solar or UV radiation) on the NIO/OA process were investigated. The process was closely related to the concentration of oxalate and to the pH value as well. The optimal MB photodegradation was found with 4 × 10−³ M of OA at pH = 3. Use of 2.0 % of ter-butanol, as a scavenger of hydroxyl radicals, confirmed the main involvement of these entities in in the MB’s photodegradation mechanism.