title: Removal of methylene blue from water by gamma-MnO2.
abstract: Methylene blue (MB) is a cationic dyestuff, which is particularly resistant to biodegradation. The molecular sieved gamma-MnO2 was used as an adsorbent/oxidant to remove the MB at room temperature and in visible light. The removal efficiency was mainly evaluated by X-ray diffractometer (XRD), UV-Vis spectrometer (UV-Vis), total organic carbon (TOC). The results revealed that the mechanisms of MB removal by gamma-MnO2 are significantly influenced by the pH. In acidic conditions, hypsochromic effects (i.e. blue shifts of UV-Vis spectra) resulting from N-demethylation of the dimethylamino group in MB may occur concomitantly with oxidative degradation by gamma-MnO2. However, the TOC in solution after gamma-MnO2 treatment in acidic conditions did not show a dramatic decrease. At near neutral pH conditions, there was almost no UV-Vis absorption for the MB solution, however, only 50% TOC removal was observed. It indicated that MB was not only adsorbed onto gamma-MnO2 but also partially oxidatively degraded to other organic compounds which were colourless for UV-Vis.
authors.affiliation: Department of Safety, Health, and Environmental Engineering, Ming Chi University of Technology, 84 Gung-Juan Road, Taishan, New Taipei City, Chinese Taiwan.
authors.forename: W H
authors.initials: WH
authors.lastname: Kuan
authors.forename: C Y
authors.initials: CY
authors.lastname: Chen
authors.forename: C Y
authors.initials: CY
authors.lastname: Hu
mesh_terms: D017895:Manganese Compounds / Q000737:chemistry*; D008751:Methylene Blue / Q000302:isolation & purification*; D010087:Oxides / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: D017895:Manganese Compounds; D010087:Oxides; D014874:Water Pollutants, Chemical; D008751:Methylene Blue; C016552:manganese dioxide