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
N1 - Funding Information:
This research was supported by the National Science Foundation ( CBET 1132779 ). Graduate student support was partially provided by a Science Foundation Arizona fellowship. Materials were characterized in the LeRoy Eyring Center for Solid State Science at Arizona State University. Appendix A
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
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U2 - 10.1016/j.apcatb.2013.01.042
DO - 10.1016/j.apcatb.2013.01.042
M3 - Article
AN - SCOPUS:84874367261
SN - 0926-3373
VL - 136-137
SP - 40
EP - 47
JO - Applied Catalysis B: Environmental
JF - Applied Catalysis B: Environmental
ER -