Effect of bromide ion on the reaction pathway between hydroxyl radical and glycine
2015
Ying, Liwen | Dong, Wenbo | Yuan, Haixia | Liu, Yan | Ma, Luming
Br⁻and nitrogen-containing organic pollutants, such as amino acids, protein, etc., were often detected in water and wastewater treatment plants using advanced oxidation technologies. All these technologies have one common characteristic, that is, the removal processes involve ·OH. Therefore, it is necessary to study the different reaction pathways among ·OH, Br⁻, and amino acids. In this research, glycine was chosen as the representative of amino acids and H₂O₂was selected as ·OH precursor. Results showed that Br⁻had a shielding effect on H of α-carbon in glycine, when it was abstracted by ·OH. The main reaction pathway in the system containing Br⁻was the abstraction of H from amino group in glycine by ·OH, contributing 85 % of total abstracted H. This system had a prominent phenomenon of decarboxylation and performed as alkali production dominating. However, in the system not containing Br⁻, the main reaction pathway was the abstraction of H from α-carbon in glycine by ·OH, contributing 97 % of total abstracted H. This system performed as acid production dominating. By laser flash photolysis, the second-order rate constants of abstraction of H from both α-carbon and amino group in glycine by ·OH were obtained as (3.3 ± 0.5) × 10⁷M⁻¹·s⁻¹and (8.2 ± 0.8) × 10⁸ M⁻¹·s⁻¹, respectively. The second-order rate constants of the reaction between H₂NCH₂COO⁻, HṄCH₂COO⁻ and H₂O₂ were (1.5 ± 1.1) × 10⁷ M⁻¹·s⁻¹and (4.4 ± 0.3) × 10⁷ M⁻¹·s⁻¹, respectively. In addition, Br⁻was found to play a catalytic role in the decomposition of H₂O₂under UV radiation. The results mentioned above were significant for the application of advanced oxidation technologies for water containing both amino acids and Br⁻in water and wastewater treatment plants.
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