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Photocatalytic nitrate reduction in water: Managing the hole scavenger and reaction by-product selectivity

Paper ID Volume ID Publish Year Pages File Format Full-Text
46308 46437 2013 8 PDF Available
Title
Photocatalytic nitrate reduction in water: Managing the hole scavenger and reaction by-product selectivity
Abstract

Nitrate contamination of groundwater limits it use as a drinking water supply unless the nitrate is removed. The aim of this study was to move toward implementing photocatalysis for nitrate treatment in drinking water systems by understanding the effects of experimental conditions and the mechanisms involved. Specifically, the photocatalytic reduction of nitrate in water was examined using titanium dioxide (Evonik P90) loaded with silver nanoparticles and formate as a hole scavenger (electron donor). Experimental conditions including pH, nitrate concentration, formate concentration, photocatalyst concentration, and silver loading were varied to demonstrate their effect on the rate of nitrate and formate removal as well as by-product selectivity. For drinking water applications, minimization of residual formate is essential to prevent adverse effects in potable water distribution systems (e.g., carbon source for biofilm growth). The experimental stoichiometric requirement for formate indicated that it acts as a two-hole scavenger, which suggests conduction band electrons, rather than radicals, are responsible for nitrate reduction. Using optimal operating conditions, nitrate and formate were efficiently removed at nearly a 1:1 ratio, showing that the residual hole scavenger concentration can be controlled while maintaining an acceptable rate. Compared to P90 alone, the addition of silver nanoparticles improved the rate of nitrate and formate removal significantly, reduced the overpotential for nitrate reduction, and provided a more positive surface charge. The removal rates decreased with increasing pH, which suggests that the reaction is a proton-coupled electron reaction and that adsorption of the constituents is necessary for effective charge transfer. Under acidic conditions (pH = 2.5), nitrogen gases (∼85%) and ammonium (∼15%) were the final by-products. Between pH 3.5 and 4, a sudden by-product switch occurred to nitrite, suggesting that, at higher pH, a co-catalyst that is efficient at localizing protons is required to move beyond nitrite.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Stoichiometric evidence is provided showing formic acid acts as a two-hole scavenger and that nitrate/formate can be removed at a 1:1 ratio. ► Silver is present as a metallic core with an oxide shell and reduces the overpotential for nitrate reduction at neutral pH. ► Nitrate reduction occurs through a step-wise reduction via multi-electron transfers. ► Proton localization at the reaction site is necessary to move beyond nitrite.

Keywords
Titanium dioxide; Photocatalysis; Silver; Nitrate; Formate; Hole scavenger
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Photocatalytic nitrate reduction in water: Managing the hole scavenger and reaction by-product selectivity
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volumes 136–137, 5 June 2013, Pages 40–47
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