Advanced oxidation of calmagite using in situ generated hydrogen peroxide catalyzed by manganese(II) ions and bicarbonate Ye Cao and Tippu Sheriff Queen Mary University of London, UK The discharge of azo dyes, that possess the stable –N=N– unit, are threatening the aquatic ecosystem since they are toxic to organisms and difficult to degrade by traditional water treatment technologies. 1 An in situ advanced oxidation process is proposed here to address the water pollution caused by azo dye discharge, which involves the formation of [Mn II T 2 ] 6- (where TH 2 = 1,2-dihydroxybenzene-3,5-disulfonate, disodium salt (Tiron), Fig. 1(a)) as the catalyst for the in situ generation of H 2 O 2 , and bicarbonate as a co-catalyst for the oxidative degradation of Calmagite (CAL, 2-hydroxy-1-(2-hydroxy-5-methylphenylazo)-4-naphthalenesulfonic acid, Fig. 1(b)), which is a typical azo dye, at room temperature. A one-eighth-lives method 2 was applied to investigate the effect of pH, buffer type and Mn 2+ concentration on the degradation of CAL. Mn(IV)=O, was found to be the main reactive species, while percarbonate () and hydroxyl radicals () were the subsidiary reactive species for CAL degradation (Fig. 2). Using HPLC/ESI-MS, the degradation intermediates of CAL were identified as 1-amino-2-naphthol- 4-sulfonate ion, 1-amino-2-naphthol-4-sulfinic ion, 1-amino-2-naphthol and 1-nitroso-2-naphthol. This work demonstrates that the in situ generation of H 2 O 2 system catalyzed by Mn 2+ can efficiently degrade CAL under ambient conditions in aqueous solution. 3 In addition, we have showed this system can be used as an anti-corrosion and anti-bacteria formulation by the consumption of dissolved O 2 and the in situ generation of H 2 O 2 . We are currently investigating the use of Cu II as the catalyst in activating the in situ generated H 2 O 2 for the degradation of more stable pollutants like 4,4'-(Hexafluoroisopropylidene)diphenol (BPAF, Fig. 1(c)). This work will include an investigation of the degradation mechanism, the degradation kinetics, the degradation pathways, the concentration variation of reactive oxidant species such as , and the influence of co-existing anions such as chloride, sulfate, and nitrate on degradation. Preliminary results are promising and will be presented in the poster.
Fig 1. The Chemical structures of (a) Tiron, (b) Calmagite and (c) BPAF
Fig 2. The in situ generation of H 2 O 2 and its use for the oxidative degradation of CAL References 1. X. Meng, B. Scheidemantle, M. Li, Y.-y. Wang, X. Zhao, M. Toro-González, P. Singh, Y. Pu, C. E. Wyman, S. Ozcan, C. M. Cai and A. J. Ragauskas, ACS Omega , 2020, 5 , 2865-2877. 2. J. Peng, X. Lu, X. Jiang, Y. Zhang, Q. Chen, B. Lai and G. Yao, Chem. Eng. J. , 2018, 354 , 740-752. 3. Y. Cao and T. S. Sheriff, Chemosphere , 2022, 286 , 131792.
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