Department of Safety, Health, and Environmental Engineering, Ming Chi University of Technology, 84 Gung-Juan Road, Taishan, New Taipei City, Chinese Taiwan.
Water Sci Technol. 2011;64(4):899-903. doi: 10.2166/wst.2011.262.
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.
亚甲蓝（MB）是一种阳离子染料，特别耐生物降解。分子筛γ-MnO2 被用作吸附剂/氧化剂，在室温下和可见光下去除 MB。去除效率主要通过 X 射线衍射仪 (XRD)、紫外可见分光光度计 (UV-Vis) 和总有机碳 (TOC) 进行评估。结果表明，γ-MnO2 去除 MB 的机制受 pH 值的显著影响。在酸性条件下，MB 中二甲基氨基的 N-去甲基化可能会同时发生，导致紫外可见光谱发生蓝移（即蓝移），同时被 γ-MnO2 氧化降解。然而，在酸性条件下用 γ-MnO2 处理后溶液中的 TOC 并没有明显下降。在近中性 pH 条件下，MB 溶液几乎没有紫外可见吸收，但仅观察到 50%的 TOC 去除。这表明 MB 不仅被吸附到 γ-MnO2 上，而且部分被氧化降解为其他无色的有机化合物，这些化合物对紫外可见没有吸收。
