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Influence of pH and pH adjustment conditions on photocatalytic oxidation of aqueous ammonia under airflow over Pt-loaded TiO2

Paper ID Volume ID Publish Year Pages File Format Full-Text
39353 45819 2015 6 PDF Available
Title
Influence of pH and pH adjustment conditions on photocatalytic oxidation of aqueous ammonia under airflow over Pt-loaded TiO2
Abstract

•The pH and the concentration of ammonia strongly affected the selectivity.•Under the conditions of [NH3]i 100 mM at pH 10, the main product was nitrogen.•The presence of NaHCO3–Na2CO3 lowered the rate and the selectivity for nitrogen.•The amount of ammonia adsorbed on Pt-TiO2 affected the rate and the selectivity.

The influence of pH and pH adjustment conditions on the photocatalytic oxidation of aqueous ammonia in the presence of Pt-TiO2 under airflow was investigated as a possible treatment for ammonia-containing wastewater. Ammonia oxidation proceeded only under alkaline conditions, and the maximum initial oxidation rate was obtained at pH ∼ 10. The pH of the reaction suspension decreased with the formation of nitrite and nitrate species, stopping completely when the pH fell below 7 for reactions in which the initial pH (pHi) was adjusted within the range 8.7–11.3 using NaOH(aq). The rate of ammonia oxidation was higher when NaOH(aq) was used to adjust the pHi than that achieved using Na2CO3–NaHCO3 buffer solution at the same pH. The maximum ammonia adsorption on Pt-TiO2 (measured under dark conditions) was obtained at pH 10 and the amount of ammonia adsorbed when the pHi was adjusted with NaOH(aq) was higher than that achieved using the Na2CO3–NaHCO3 buffer solution at the same pH; thus, the amount of adsorbed ammonia strongly affected the oxidation rate. Although the selectivity for the sum of the undesired products, nitrite and nitrate was high when the ammonia concentration was low (e.g., 5 mM), the selectivity decreased as the initial ammonia concentration increased for each pH and pH adjustment condition. Suppression of the selectivity was evident when the pHi was adjusted to 10 with NaOH(aq). The selectivity was affected by the changes in the density of N-containing species on the photocatalyst surface as the pH and pH adjustment conditions were varied.

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Keywords
Ammonia; Photocatalysis; Water treatment; Wastewater; pH; Titanium dioxide; Nitrogen; Nitrate
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Influence of pH and pH adjustment conditions on photocatalytic oxidation of aqueous ammonia under airflow over Pt-loaded TiO2
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 496, 25 April 2015, Pages 73–78
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us