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.

Original languageEnglish (US)
Pages (from-to)40-47
Number of pages8
JournalApplied Catalysis B: Environmental
Volume136-137
DOIs
StatePublished - Jun 5 2013

Fingerprint

formic acid
scavenger
Nitrates
Byproducts
nitrate
Water
Potable water
Drinking Water
water
Silver
silver
drinking water
Nitrites
electron
nitrite
Electrons
Protons
by-product
Nanoparticles
Hole concentration

Keywords

  • Formate
  • Hole scavenger
  • Nitrate
  • Photocatalysis
  • Silver
  • Titanium dioxide

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology
  • Environmental Science(all)

Cite this

Photocatalytic nitrate reduction in water : Managing the hole scavenger and reaction by-product selectivity. / Doudrick, K.; Yang, T.; Hristovski, Kiril; Westerhoff, Paul.

In: Applied Catalysis B: Environmental, Vol. 136-137, 05.06.2013, p. 40-47.

Research output: Contribution to journalArticle

@article{8938811a16a24f7e878467f901170908,
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.",
keywords = "Formate, Hole scavenger, Nitrate, Photocatalysis, Silver, Titanium dioxide",
author = "K. Doudrick and T. Yang and Kiril Hristovski and Paul Westerhoff",
year = "2013",
month = "6",
day = "5",
doi = "10.1016/j.apcatb.2013.01.042",
language = "English (US)",
volume = "136-137",
pages = "40--47",
journal = "Applied Catalysis B: Environmental",
issn = "0926-3373",
publisher = "Elsevier",

}

TY - JOUR

T1 - Photocatalytic nitrate reduction in water

T2 - Managing the hole scavenger and reaction by-product selectivity

AU - Doudrick, K.

AU - Yang, T.

AU - Hristovski, Kiril

AU - Westerhoff, Paul

PY - 2013/6/5

Y1 - 2013/6/5

N2 - 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.

AB - 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.

KW - Formate

KW - Hole scavenger

KW - Nitrate

KW - Photocatalysis

KW - Silver

KW - Titanium dioxide

UR - http://www.scopus.com/inward/record.url?scp=84874367261&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84874367261&partnerID=8YFLogxK

U2 - 10.1016/j.apcatb.2013.01.042

DO - 10.1016/j.apcatb.2013.01.042

M3 - Article

VL - 136-137

SP - 40

EP - 47

JO - Applied Catalysis B: Environmental

JF - Applied Catalysis B: Environmental

SN - 0926-3373

ER -