title: Oxidative degradation of azo dyes using tourmaline.
abstract: This study aimed to investigate the catalyzed degradation ability of tourmaline on the dyes methylene blue (MB), rhodamine B (RhB), and congo red (CR) at different pH values. Interestingly, tourmaline strongly adsorbed anionic dyes, but it did not adsorb cationic dyes. When H₂O₂ was introduced into the tourmaline-dye systems, the degradation percentage for CR catalysis by tourmaline was lower than the percentage of adsorption, whereas the opposite was true for MB and RhB systems. Notably, the catalyzed degradation decreased from 100% to 45% for MB, 100% to 15% for RhB and 100% to 25% for CR as the pH increased from 3.0 to 10.0, respectively, which was much greater than the degradation obtained for previously reported materials at pH values ranging from 4.0 to 10.0. Tourmaline catalytically degraded the dyes over a broad range of pH values, which was attributed to tourmaline automatically adjusting the pH of the dye solutions to approximately 5.5 from an initial range of 4.2-10.0. An electron paramagnetic resonance spin trapping technique observed peroxyl (ROO·) and alkoxy (RO·) or alkyl (R·) radicals originated from the attack of ·OH radicals and O₂(·-) radicals, indicating that these radicals were involved in the catalyzed degradation of MB. Importantly, four intermediate products of MB at m/z 383, 316, 203 and 181 were observed by LC/MS.
authors.affiliation: MOE Key Laboratory of Pollution Process and Environmental Criteria, College of Environment Science and Engineering, Nankai University, Tianjin 300071, PR China. wangcuipping0@163.com
authors.forename: Cuiping
authors.initials: C
authors.lastname: Wang
authors.forename: Yanwei
authors.initials: Y
authors.lastname: Zhang
authors.forename: Li
authors.initials: L
authors.lastname: Yu
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Zhang
authors.forename: Hongwen
authors.initials: H
authors.lastname: Sun
mesh_terms: D000327:Adsorption; D001391:Azo Compounds / Q000032:analysis* / Q000737:chemistry; D002384:Catalysis; D004396:Coloring Agents / Q000032:analysis* / Q000737:chemistry; D003224:Congo Red / Q000032:analysis / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste; D008751:Methylene Blue / Q000032:analysis / Q000737:chemistry; D008903:Minerals / Q000737:chemistry*; D009930:Organic Chemicals; D010100:Oxygen / Q000737:chemistry*; D010545:Peroxides; D012235:Rhodamines / Q000032:analysis / Q000737:chemistry; D017640:Silicates / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013783:Textile Industry; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry; D018508:Water Purification / Q000379:methods
chemical_list: D001391:Azo Compounds; D004396:Coloring Agents; D005609:Free Radicals; D007220:Industrial Waste; D008903:Minerals; D009930:Organic Chemicals; D010545:Peroxides; D012235:Rhodamines; D017640:Silicates; D014874:Water Pollutants, Chemical; C049375:perhydroxyl radical; D003224:Congo Red; D012822:Silicon Dioxide; D006861:Hydrogen Peroxide; C029773:rhodamine B; D010100:Oxygen; D008751:Methylene Blue
keywords: Dye; EPR; Intermediate products; Tourmaline