title: Removal of cationic dye methylene blue by zero-valent iron: Effects of pH and dissolved oxygen on removal mechanisms.
abstract: Effects of pH and dissolved oxygen on mechanisms for decolorization and total organic carbon (TOC) removal of cationic dye methylene blue (MB) by zero-valent iron (ZVI) were systematically examined. Decolorization and TOC removal of MB by ZVI are attributed to the four potential mechanisms, i.e. reduction, degradation, precipitation and adsorption. The contributions of four mechanisms were quantified at pH 3.0, 6.0 and 10.0 in the oxic and anoxic systems. The maximum efficiencies of decolorization and TOC removal of MB were found at pH 6.0. The TOC removal efficiencies at pH 3.0 and 10.0 were 11.0 and 17.0%, respectively which were considerably lower as compared with 68.1% at pH 6.0. The adsorption, which was favorable at higher pH but was depressed by the passive layer formed on the ZVI surface at alkaline conditions, characterized the effects of pH on decolorization and TOC removal of MB. The efficiencies of decolorization and TOC removal at pH 6.0 under the anoxic condition were 73.0 and 59.0%, respectively, which were comparable to 79.9 and 55.5% obtained under the oxic condition. In the oxic and anoxic conditions, however, the contributions of removal mechanisms were quite different. Although the adsorption dominated the decolorization and TOC removal under the oxic condition, the contribution of precipitation was largely superior to that of adsorption under the anoxic condition.
authors.affiliation: a Research Center for Chemical and Environmental Engineering, Department of Applied Chemistry , Toyo University , Kawagoe, Saitama , Japan.
authors.forename: Xuan
authors.initials: X
authors.lastname: Sun
authors.forename: Tomoyo
authors.initials: T
authors.lastname: Kurokawa
authors.forename: Moe
authors.initials: M
authors.lastname: Suzuki
authors.forename: Minoru
authors.initials: M
authors.lastname: Takagi
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kawase
mesh_terms: D000327:Adsorption; D004791:Enzyme Inhibitors / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008751:Methylene Blue / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
chemical_list: D004791:Enzyme Inhibitors; D014874:Water Pollutants, Chemical; D007501:Iron; D010100:Oxygen; D008751:Methylene Blue
keywords: Dissolved oxygen; methylene blue; removal mechanism; solution pH; zero-valent iron