Application of an active immobilized iron oxide with catalytic H₂O₂ for the mineralization of phenol in a batch photo-fluidized bed reactor

A batch photo-fluidized bed reactor (photo-FBR) is designed for the mineralization of phenol and the minimization of iron species leached from an active immobilized iron oxide (denoted as SiG2). The hydroxyl radical ({radical dot}OH), which is produced from the reaction of hydrogen peroxide (H₂O₂) and SiG2 under irradiation by a 400-W Hg-vapor lamp, was confirmed by electron paramagnetic resonance signals of 5,5-DIMETHYL-1-pyrroline-N-oxide (DMPO)-{radical dot}OH (aqueous solution). The mineralization of phenol was more efficient in the presence of light. In general, a decrease of solution pH is commonly ascribed to the formation of carboxylic acids (acetic acid, oxalic acid, formic acid etc.) during the degradation of phenol. However, in this study, an interesting phenomenon was observed. The solution pH first decreased and then rose during the reaction in the presence of light. Also, in this case, the variation of solution pH reflected the degree of mineralization in this study. The approximately 98% mineralization of phenol led to fewer iron species being leached from SiG2 in the photo-FBR. A savings of more than 40% of the H₂O₂ dosage required for the phenol mineralization process was confirmed. In a batch photo-FBR, the system loading reflects the ratio of catalyst weight to the reaction volume. About 96%, 86% and 11% of the total organic carbons were removed after 180 min, resulting in catalyst weight to reaction volume ratios of 30:1, 20:1 and 13:1, respectively. The activity of SiG2 did not decline after six reactions. The reactions for photo-assisted SiG2 in the presence of hydrogen peroxide and phenol were summarized.