Journal of The Electrochemical Society, 163 (14) E421-E427 (2016) E421 Fabrication and Characterization of a Cu-Zn-TiO2 Nanotube Array Polymetallic Nanoelectrode for Electrochemically Removing Nitrate from Groundwater Fang Liu,a,b,c Miao Li,a,c,z Hao Wang,d Xiaohui Lei,d Lele Wang,a and Xiang Liua,z a School of Environment, Tsinghua University, Beijing 100084, China b College of Architecture & Civil Engineering, Beijing University of Technology, Beijing 100124, China c Key Laboratory of Solid Waste Management and Environment Safety (Tsinghua University), Ministry of Education, Tsinghua University, Beijing 100084, China d State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China A novel Cu-Zn-TiO2 nanotube array (TNTA) polymetallic nanoelectrode, intended to improve the electrochemical nitrate removal efficiency, was fabricated The nanoelectrode was fabricated by plating Cu onto a Ti nanoelectrode and then plating Zn onto the Cu/Ti bilayer electrode produced The Ti nanostructures on the Cu-Zn-TNTA nanoelectrode surface gave the nanoelectrode a large specific surface area, and the Zn and Cu gave the nanoelectrode a high electrocatalytic activity for reducing nitrate Scanning electron microscopy images showed that the Cu-Zn-TNTA polymetallic nanoelectrode had a honeycomb structure with spongy deposits X-ray diffractometry results showed that the Cu-Zn-TNTA nanoelectrode predominantly contained Cu, O, Ti, and Zn The nitrate removal efficiency of the Cu-Zn-TNTA nanoelectrode was 345.7% of the removal efficiency for a Ti nanoelectrode The presence of NaCl allowed both the cathodic reduction of nitrate and the anodic oxidation of the ammonia and nitrite byproducts to be achieved with high removal efficiencies, especially using an IrO2 anode In the present of NaCl, nitrate removal rate was 93.4% in current density of 30 mA/cm2 after 90 Nitrate was completely removed using the IrO2 anode, and little ammonia was detected in the treated solution The reduction efficiency increased slightly as the initial nitrate concentration increased through the range 20–100 mg/L, and the pH had little effect on the nitrate reduction efficiency © The Author(s) 2016 Published by ECS This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited [DOI: 10.1149/2.1391614jes] All rights reserved Manuscript submitted August 15, 2016; revised manuscript received October 5, 2016 Published November 25, 2016 Water resource shortages have become increasingly serious in recent years, and are aggravated by groundwater pollution Nitrate is an important groundwater pollutant, and removing nitrate from groundwater is attracting increasing amounts of attention.1 Major anthropogenic sources of nitrate in groundwater are industrial wastewater, domestic sewage, animal waste, nitrogen fertilizers, and other waste liquids.2–4 The World Health Organization has set a guideline maximum nitrate concentration in drinking water of 45 mg/L, and the European Union regulatory limit is 50 mg/L for regular potable water and 15 mg/L for water ingested by infants.5–7 High nitrate concentrations in drinking water can seriously harm human health, impairing oxygen transport to the tissues The ingestion of nitrate can cause several health problems, including congenital deformities, gastric cancer, high blood pressure, mental decline, thyroid disorders (e.g., goiter), and visual and auditory problems, which develop relatively slowly.8–13 Attention has therefore been given to developing methods for removing nitrate from groundwater Various methods have been proposed for the removal of nitrate such as biological, physicochemical, chemical and electrochemical.4 Biological method has various disadvantages e.g it need a long time to react, difficult to control, react incomplete will release of NO2, N2 O and NOx , produced a large number of biological sludge, requires a constant supply of the organic substrate This limits the biological removal of nitrate application.14,15 The physicochemical processes mainly include distillation, reverse osmosis, electrodialysis, ion exchange,16,17 it would produce secondary brine wastes, because the nitrates are merely separated but not destroyed The chemical methods produce toxic byproducts, such as nitrite and ammonia and require either large quantities of metals or hydrogen as reducing agent.4 In recent years, attention has been particularly focused on electrochemical methods of removing nitrate from water Electrochemical methods have advantages such as no demand for chemicals before or after the treatment, no sludge produce, small area occupied by the plant and low investment costs.4,18–24 The efficiency at which z E-mail: watersml@126.com; x.liu@tsinghua.edu.cn nitrate is removed using such methods depends strongly on the material the electrode is made from The broad practical use of electrochemical nitrate reduction requires a material to be found with appropriate electrocatalytic properties.3 The abilities of electrodes made out of various materials, including alloys, diamonds, metals, metal complexes, and materials with adatoms, to remove nitrate have previously been studied.25–27 Large numbers of metal electrodes, including Cu, Ni, and Zn electrodes, have been studied Ti and other substrates offer promise for use in environmental applications because they are relatively resistant to corrosion Pt has a low nitrate reduction activity, whereas Cu and Zn are much more active.3,4 Electrodes made of two metals often have higher catalytic activities than electrodes made of one metal Using a Cu/Zn cathode and a Pt anode has been found to give a high electrocatalytic activity for nitrate Using a Cu/Zn cathode, Cu catalyzes the reduction of NO3 − to NO2 − and Zn catalyzes the reduction of NO2 − to the final product.28 Materials containing nanostructures are generally called nanomaterials It has been shown that nanostructures on the surface of a metal electrode can improve the electrochemical reduction performance of the electrode.29 This could be caused by the nanostructures giving the nanoelectrode a large specific surface area Despite the good results that nanoelectrodes have given, nanoelectrodes are limited by the poor reproducibility achieved when preparing their activated surfaces Modified nanoelectrodes that can be prepared reproducibly are therefore required To the best of our knowledge, polymetallic nanoelectrodes have not previously been used to electrochemically reduce nitrate The purpose of this study was to develop a novel and highly efficient polymetallic nanoelectrode for electrochemically reducing nitrate We fabricated a Cu-Zn-TiO2 nanotube array (TNTA) polymetallic nanoelectrode and investigated its nitrate reduction performance We developed a nanoelectrode fabrication method and optimized the method to allow a nanoelectrode to be produced that could very efficiently remove nitrate using nontoxic materials The mechanism involved the removal of nitrate The efficiency of the nanoelectrode under different experimental conditions was investigated Downloaded on 2017-03-10 to IP 80.82.77.83 address Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract) E422 Journal of The Electrochemical Society, 163 (14) E421-E427 (2016) removed the Ti sheet, rinsed the plate surface with deionized water and then dried the Ti sheet with blower At the end of the process, a Ti nanoelectrode had been fabricated Step B The Cu catalyst middle layer was deposited on the surface of the Ti nanoelectrode fabricated in step A It was necessary to ensure that only Cu was present on the nanoelectrode surface Cu was electrodeposited from a 180 g/L CuSO4 solution in 60 g/L H2 SO4 using a deposition current of 0.15 A for 10 s At the end of the process a Cu/Ti bilayer nanoelectrode had been fabricated Step C A Zn catalyst layer was deposited on the surface of the Cu/Ti bilayer nanoelectrode produced in step B It was necessary to ensure that only Zn was present on the nanoelectrode surface Zn was electrodeposited from 160 g/L KCl and 80 g/L ZnCl2 solution in 500 μL of a HCl using a deposition current of 0.25 A for 10 s At the end of this process a Cu-Zn-TNTA polymetallic nanoelectrode had been fabricated Figure Schematic diagram of the electrochemical apparatus Experimental Materials and chemicals.—Two cylindrical electrolytic cells were prepared, one with a networking volume of 100 mL and the other with a networking volume of 150 mL Each electrolytic cell was made out of acryl material We used an undivided electrolytic cell, Compared with a divided cell need to add a layer of membrane between the cathode and anode which need higher cost, more complex structure, through the experiment we found that not add membrane also be able to get a better removal effect, so we used the undivided electrolytic cell Chemicals used in this study include: NaSO4, HCl, HF, Acetic acid, H2 SO4 , ZnCl2 , NH2 SO3 H, KCl and CuSO4 · 5H2 O All chemicals were of analytical grade and used without further purification Solutions were prepared with deionized water (18.2 M/cm, ELGASTAT B124 Water Purification Unit, The Elga group, England) Solutions and chemicals are identical in the present study Fresh electrolyte was used for each electrolysis Electrodes.—Each electrolytic cell (shown schematically in Fig 1) was made out of an acrylic material Initially, a graphite plate was used as the cathode and a Ti plate as the anode When the Cu-ZnTNTA was being developed, first of all, Ti nanoelectrode was used as the cathode and a Cu plate was used as the anode, and then Cu plated on a Ti nanoelectrode was used as the cathode and a Zn plate was used as the anode Nitrate in an aqueous solution was reduced using the Cu-Zn-TNTA nanoelectrode as the cathode and a Pt plate as the anode Each electrode was 2.5 cm wide, mm thick, and 10 cm high The gap between the electrodes was 0.8 cm Methods.—Synthesis of the Cu-Zn-TNTA nanoelectrode.—According to the Wang’s reports,30 Ti sheet was used to fabricate Ti nanoelectrode Before fabrication, the sheet was polished with sandpaper until the surface showed no scratches, followed by rinsing in deionized water and drying in air In the process of nanoelectrode fabrication Ti foil as the cathode and an iridium dioxide foil as the anode In our study, each electrode was 2.5 cm wide, 10 cm high and mm thick The gap between the electrodes was 0.8 cm In the process of nanoelectrode fabrication Ti foil (99.6% purity) as the anode and an graphite foil as the cathode The surface of the anode was mechanically polished with 800–1200 SiC metallographic paper and washed several times with deionized water The fabrication procedure had three steps, described below Step A A 150 mL aliquot of a 1:10 mixture of acetic acid and water containing 0.05 wt% HF was poured into the 150 mL electrolysis cell The process was performed at room temperature A voltage of 25 V was applied for h After hours, turned off the dc power supply, Nitrate removal.—A solution with an initial nitrate concentration of 50 mg/L was prepared A 100 mL aliquot of the solution was poured into the electrolytic cell, then the reaction was started by applying a current density of 30 mA/cm2 The solution used in each experiment contained 0.5 g/L Na2 SO4 to increase the conductivity of the solution A 1.0 mL sample was removed from the electrolytic cell at specified intervals Each sample was analyzed to allow temporal changes in the nitrate concentration in the solution to be monitored The effect of the current density was investigated by performing experiments at current densities of 10, 20, 30, and 50 mA/cm2 (controlled using a galvanostat) The effect of the temperature was investigated by performing experiments at 0◦ C (keeping the apparatus in an ice bath) and at 25, 40, and 60◦ C (keeping the apparatus in a water bath) Analysis method.—All analyses were carried out according to Standard Methods (APHA et al., 1998) Nitrate and nitrite were detected by a standard colorimetric method using a spectrophotometer (DR/6000 Spectrophotometer, HACH Company, Loveland, Colorado) Ammonia was measured by Nesslerization reagent spectrophotometry The determination of nitrate was based on its absorption spectra at 220 and 275 nm Nitrite and ammonia were based on its light absorption at 540 and 420 nm, respectively The microstructure and morphology of electrodes are analyzed by field-emission scanning electron microscopy (SEM) (Hitachi S5500, Japan) and energy dispersive spectroscopy (EDS) (Hitachi S5500, Japan) Results and Discussion Characterization and the electrochemical denitrification activity of the Cu-Zn-TNTA nanoelectrode.—All experiments for nitrate removal were at room temperature with current density of 30 mA/cm2 , Figure Removal rates achieved using (A) the Ti electrode, (B) the Ti nanoelectrode, and (C) the Cu-Zn-TNTA nanoelectrode (plating Cu: 0.15 A for 15 s, plating Zn 0.2 A for 10 s), (D) the Cu-Zn-TNTA nanoelectrode (plating Cu: 0.15 A for 10 s, plating Zn 0.15 A for s), and (E) the Cu-Zn-TNTA nanoelectrode (plating Cu: 0.15 A for 10 s, plating Zn 0.25 A for 10 s) Downloaded on 2017-03-10 to IP 80.82.77.83 address Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract) Journal of The Electrochemical Society, 163 (14) E421-E427 (2016) the reaction time is 90 minutes The nitrate removal rates for different electrodes are shown in Fig It can be seen that, when plating Cu: 0.15 A for 10 s, plating Zn 0.25 A for 10 s, the highest nitrate removal rate was obtained using the Cu-Zn-TNTA nanoelectrode and the lowest using the Ti cathode The nitrate removal rate increased as the treatment time increased for all of the electrodes, and reached 21.3%, 28.3%, 65.1%, 73.3%, and 97.5% at 90 using the Ti electrode, Ti nanoelectrode, and three Cu-Zn-TNTA nanoelectrode with different current and time, respectively We attempted to determine why the polymetallic nanoelectrode had a good effect on nitrate removal by analyzing the surface morphologies and elemental compositions of the Ti electrode, Ti nanoelectrode, and Cu-Zn-TNTA nanoelectrode The surface morphologies and elemental compositions were analyzed by field-emission scanning electron microscopy and energy dispersive spectroscopy, respectively It can be seen from Fig that the Ti electrode surface was smooth, the Ti nanoelectrode surface had a loose honeycomb configuration with numerous micropores, and the Cu-Zn-TNTA nanoelectrode surface had a honeycomb structure with spongy deposits on it Energy dispersive spectra of the Ti electrode, Ti nanoelectrode, and Cu-Zn-TNTA nanoelectrode are shown in Fig The Ti electrode contained 100 wt% Ti, the Ti nanoelectrode contained 65.73 wt% Ti and 34.27 wt% O, and the Cu-Zn-TNTA nanoelectrode contained 43.04 wt% Ti, 28.97 wt% O, 15.99 wt% Zn, and 5.95 wt% Cu M´acov´a found that Zn plus Cu contents of 30 wt% to 41 wt% significantly affect the current density kinetics, increasing the electrocatalytic activity for the reduction of nitrate Our results did not agree with the results found by M´acov´a, possibly because the copper layer on our nanoelectrode was uneven The energy dispersive spectrum acquired where less copper plating had occurred, shown in Fig 5, confirmed this conclusion It can be seen from Fig that O, Ti, and Zn were basically evenly distributed but that a small proportion of the Ti was completely covered by Cu (from the Ti elemental distribution) However, Cu was concentrated in certain areas, possible because the Cu particles were large and a short plating time was used, meaning that it would be difficult to achieve a uniform distribution of Cu The Cu-Zn-TNTA nanoelectrode gave a higher nitrate removal rate when plating Cu with 0.15 A was applied for 10 s and plating Zn with 0.25 A was applied for 10 s than the other electrodes gave, and we assumed that this was because the nanostructure of the Ti surface in the Cu-Zn-TNTA nanoelectrode improved the electroanalytical performance This could have been caused by the presence of more reactive sites on the Cu-Zn-TNTA nanoelectrode than on the other electrodes and possibly by the effect of the nanostructure of the surface of the Cu-Zn-TNTA nanoelectrode on diffusion Adding Cu enhanced the catalysis of the nitrate reduction reaction In a previous study, a Zn cathode was found to have a higher electrocatalytic activity for the reduction of NO3 − than did other cathodes Keita found that adding Zn2+ to the electrolyte positively affected cathodic reduction of NO2 − , indicating that Zn is a suitable complementary cathode metal to Cu in terms of reaction kinetics Cu catalyzed the reduction of NO3 − to NO2 − and Zn catalyzed the reduction of NO2 − to the final product The current applied and the plating time strongly affected the effectiveness of the fabricated nanoelectrode Cu and Zn may not have adhered to the electrode surface if a low current and short plating time were used However, too much Cu and Zn may have adhered to the electrode surface if a high current and long plating time were used This could have caused the nanoholes in the Ti surface to become filled with Cu and Zn In Z MACOVA and K BOUZEK’s28 study, they provide a comparative study of the electrocatalytic activity of electrodes with different Cu:Zn ratios for NO3 − reduction In their research, using an electrode containing 30, 35, 41 wt% Zn, the kinetic current densities for NO3 − reaction determined by Koutecky–Levich analysis were −125, −140, −185 A/m2 , respectively It shows that by increasing the content of Zn in the alloy its electrocatalytic activity increased So they concluded that the highest electrocatalytic activity was obtained using an electrode containing 41 wt% Zn E423 Figure Field-emission scanning electron microscopy images of the (A) Ti electrode surface, (B) Ti nanoelectrode surface, and (C) Cu-Zn-TNTA nanoelectrode surface In our study we adopted the similar proportion with Z MACOVA and K BOUZEK’s, and we controlled the proportion through control of electroplating time and electroplating current After many experiments, we found that performing the Cu plating procedure by applying 0.15 A for 10 s and performing the Zn plating procedure by applying 0.25 A for 10 s gave the best nitrate removal effect Downloaded on 2017-03-10 to IP 80.82.77.83 address Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract) E424 Journal of The Electrochemical Society, 163 (14) E421-E427 (2016) Figure Energy dispersive spectra showing the elemental compositions of the (A) Ti electrode, (B) Ti nanoelectrode, and (C) Cu-Zn-TNTA nanoelectrode Nitrate reduction performance of the Cu-Zn-TNTA nanoelectrode.—Influence of the NaCl concentration.—As mentioned above, Cu has a good electrochemical activity for the reduction of nitrate.31 However, the main product of the reduction process is NH3 This would be problematic when treating drinking water Using other methods, nitrate would be mainly reduced to nitrite, ammonia, and nitrogen (which is electrochemically inactive) The main reactions occurring during the electrochemical reduction of nitrate ions to give nitrogen and ammonia are discussed below.32 NO3 − + H2 O + 2e− = NO2 − + 2OH− NO3 − + 3H2 O + 5e− = (1/2) N2 + 6OH− NO2 − + 5H2 O + 6e− = NH3 + 7OH− [3] NO2 − + 4H2 O + 4e− = NH2 OH + 5OH− [4] 2NO2 − + 4H2 O + 6e− = N2 + 8OH− [5] 2NO2 − + 3H2 O + 4e− = N2 O + 6OH− [6] NO2 − + H2 O + e− = NO + 2OH− [7] N2 O + 5H2 O + 4e− = 2NH2 OH + 4OH− [8] 2H2 O + 2e− = H2 + 2OH− (sidereaction) [9] [1] [2] Downloaded on 2017-03-10 to IP 80.82.77.83 address Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract) Journal of The Electrochemical Society, 163 (14) E421-E427 (2016) E425 Figure Energy dispersive spectra of the elemental distributions In the present of NaCl, the effects of different anode on nitrate removal, nitrite and ammonia generation are shown in Fig We performed experiments using Pt or Ir as an anode and a NaCl concentration of 0.1, 0.3, or 1.0 g/L to identify the conditions under which the least nitrite and ammonia were produced After many experiments, we found that using an IrO2 anode and a NaCl concentration of 0.3 g/L gave a nitrate removal rate of 93.44% and generated the smallest amounts of byproducts This may have been because IrO2 has a stronger oxidizing effect than does Pt, so less ammonia and nitrite will be produced during electrolysis using an IrO2 electrode than using a Pt electrode NaCl was added because the chloride ions would form hypochlorite and hypochlorous acid Hypochlorite and hypochlorous acid have strong oxidizing properties, and will cause nitrite and ammonia to be oxidized and produce nitrate or nitrogen In the present of 0.3 g/l of NaCl, whether using Pt anode or IrO2 anode, nitrite generation are almost zero However, in the present of the 0.3 g/l of NaCl, using Pt anode, ammonia generation is 0, 8.5, 19.4, 29.1, 28.9, 1.235 mg/l respectively in 0, 10, 30, 60, 90, 120 minutes; While using IrO2 anodes, ammonia generation is 0, 0.15, 2.75, 2.95, 1, 0.04 mg/l respectively in 0, 10, 30, 60, 90, 120 minutes It can be seen that the IrO2 anodes have always maintained a low ammonia production, while Pt anodes have higher ammonia production in the middle of the reaction So we deem IrO2 is a better oxidizing agent for NH4 + and NO2 − than Pt Adding too little NaCl would cause too little hypochlorite to be produced, meaning that all of the nitrite and ammonia would not be removed Adding excess NaCl would cause competitive adsorption to occur, inhibiting nitrate removal Influences of the initial nitrate concentration and the temperature.—The effects of different initial nitrate concentrations on nitrate removal are shown in Fig 7A The selectivity of the nitrate removal process was approximately constant over the nitrate concentration range that was tested At each concentration, the nitrate removal rate rapidly decreased at the beginning of the electrolysis process However, the nitrate removal rate was almost the same at different initial nitrate concentrations The removal rate when the initial nitrate concentration was 20 mg/L was 75.8% (i.e., the nitrate concentration decreased from 20.00 to 4.83 mg/L) The removal rates when the initial nitrate concentrations were 30, 50, and 100 mg/L were 74.4%, 74.6%, and 72.6%, respectively This could have been because a thin sponge-like Cu layer formed over each Ti nanopore and a granular Zn layer formed, protecting the nanopores The influence of the reaction temperature on nitrate reduction is shown in Fig 7B The earlier experiments were performed under isothermal conditions at 25◦ C The experiments at different temperatures were performed by placing the reactor in an ice bath (i.e., at 0◦ C) or in a water bath at 25, 40, or 60◦ C Most of the experiments were performed without stirring, although mixing eventually occurred because hydrogen and oxygen bubbles formed at the cathode and anode, respectively When the temperature was uncontrolled, the temperature of the treated solution increased from 25.0◦ C at the beginning of the electrolysis process to 78◦ C after 60 of electrolysis Increasing the temperature could affect the removal of nitrate in several ways, including by increasing the diffusion rate and increasing the strength of the adsorption that occurred The nitrate removal rates were slightly higher at 40 and 60◦ C than at 25◦ C (the initial nitrate concentration of 50.00 mg/L decreased to 15.0 mg/L at 25◦ C, to 13.2 mg/L at 40◦ C, and to 8.3 mg/L at 60◦ C) This was because increasing the temperature will have favored the formation of ammonia and decreased the amount of nitrogen formed, as has been reported previously Influence of current density and pH.—The nitrate concentrations at different times when the Cu-Zn-TNTA nanoelectrode was used with different current densities are shown in Fig 8A Increasing the current Downloaded on 2017-03-10 to IP 80.82.77.83 address Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract) E426 Journal of The Electrochemical Society, 163 (14) E421-E427 (2016) Figure (A) Temporal changes in nitrate, nitrite, and ammonia concentrations using an IrO2 anode and a NaCl concentration of 0.3 g/L with current density of 30 mA/cm2 and (B) Temporal changes in nitrate, nitrite, and ammonia concentrations using an Pt anode and a NaCl concentration of 0.3 g/L with current density of 30 mA/cm2 density between 10 and 40 mA/cm2 increased the removal rate, and the removal rate was particularly high at current densities of 30 and 40 mA/cm2 Increasing the current density is a simple way of accelerating the reduction reaction but usually decreases both current efficiency and selectivity We found that the current efficiency decreased as the current density increased The current efficiency probably decreased because more hydrogen was produced in the electrode structure The potentials were 10.8–9.1, 17.3–11.5, 26.9–14.2, and 30.4–14.2 V at current densities of 10, 20, 30, and 40 mA/cm2 , respectively The current efficiency is 2.71, 1.54, 1.16, 1.08 mg/L∗ (mA/cm2∗ h)−1 in the current densities of 10, 20, 30, and 40 mA/cm2 , respectively A low current density will be economically favorable However, in practical use, selecting the most suitable current density will depend on the treatment conditions The effect of the initial pH on nitrate removal is shown in Fig 8B The solution was brought to the desired pH by adding dilute NaOH or dilute H2 SO4 The nitrate removal trends were similar at different initial pH values, and different initial pH values gave almost the same nitrate removal rates This may have been because a thin spongelike Cu layer became attached to each Ti nanopore and a granular Zn layer formed during the preparation of the nanoelectrode These Figure Effects of the (A) initial nitrate concentration and (B) temperature on temporal changes in the nitrate concentration (I = 30 mA/cm2 , 0.50 g/L Na2 SO4 ) would have prevented adhesion to the nanopores, meaning that the initial pH would have hardly affected the nitrate removal rate Conclusions A novel Cu-Zn-TNTA nanoelectrode was fabricated to improve the electrochemical nitrate removal rate The nitrate removal rates achieved using the Cu-Zn-TNTA nanoelectrode in an undivided and unbuffered cell under different conditions were determined The results showed that the Cu-Zn-TNTA nanoelectrode could be used to remove nitrate from an aqueous solution The conclusions shown below were drawn (1) (2) The electrode played an important role in nitrate removal The nitrate removal rate reached 97.5% using the Cu-Zn-TNTA nanoelectrode in the presence of 0.50 mg/L Na2 SO4 after 90 of electrolysis at a current density of 30 mA/cm2 In the presence of 0.3 g/L NaCl, nitrate was completely removed using an IrO2 anode, and little ammonia was detected in the treated solution At the same initial nitrate concentration, the nitrate removal efficiency increased as the current density increased At the same current density, the nitrate removal rate decreased slightly as the initial nitrate concentration increased The temperature strongly affected nitrate removal Changing the pH had little effect on nitrate removal Downloaded on 2017-03-10 to IP 80.82.77.83 address Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract) Journal of The Electrochemical Society, 163 (14) E421-E427 (2016) Figure Effects of the (A) current density and (B) pH on changes in the nitrate concentration over time (I = 30 mA/cm2 , 0.50 g/L Na2 SO4 ) Acknowledgments The authors thank the National Natural Science Foundation of China (No 51408335) and Beijing Natural Science Foundation (J150004) for the financial support of this work References L Szpyrkowicz, S Daniele, M Radaelli, and S Specchia, “Removal of NO3 − from water by electrochemical reduction in different reactor configurations,” Applied Catalysis B: Environmental, 66, 40 (2006) A M Stortinia, L M Morettoa, A Mardeganb, M Ongaroa, and P Ugoa, “Arrays of copper nanowire electrodes: Preparation, characterization and application as nitrate sensor,” Sensors and Actuators B, 207, 186 (2015) G E Dima, A C A de Vooys, and M T M Koper, “Electrocatalytic reduction of nitrate at low concentration on coinage and transition-metal electrodes in acid solutions,” Journal of Electroanalytical Chemistry, 554/555, 15/23 (2003) C Polatides and G Kyriacou, “Electrochemical reduction of nitrate ion on various cathodes – reaction kinetics on bronze cathode,” Journal of Applied Electrochemistry, 35, 421 (2005) E427 M Li, C P Feng, Z Y Zhang, and N Sugiura, “Efficient electrochemical reduction of nitrate to nitrogen using Ti/IrO2 –Pt anode and different cathodes,” Electrochimica Acta, 54, 4600 (2009) EEC Council Recommendations (1987) EEC Council Directive 98/83/EC (1998) American Public Health Association (APHA), Standard Methods for the Examination of Water and Wastewater, 18th Ed., American Public Health Association, Washington, DC, 1992 J Christophe, V Tsakova, and C Buess-Herman, “Electroreduction of Nitrate at Copper Electrodes and Copper-PANI Composite Layers,” Z Phys Chem., 221, 1123 (2007) 10 M Li, C P Feng, Z Y Zhang, X H Lei, R Z Chen, Y N Yang, and N Sugiura, “Simultaneous reduction of nitrate and oxidation of by-products using electrochemical method,” Journal of Hazardous Materials, 171, 724 (2009) 11 S K Gupta, A B Gupta, R C Gupta, A K Seth, J K Bassain, and A Gupta, “Recurrent acute respiratory tract infections in areas with high nitrate concentrations in drinking water,” Environ Health Perspect 108(4), 363 (2000) 12 D Majumdar and N Gupta, “Nitrate pollution of groundwater and associatedhuman health disorders,” Indian J Environ Health, 42(1), 28 (2000) 13 M Shrimali and K P Singh, “New methods of nitrate removal from water,” Environ Pollut., 112, 351 (2001) 14 S Ghafari, M Hasan, and M K Aroua, “Bio-electrochemical removal of nitrate from water and wastewater a review,” Bioresour Technol., 99, 3965 (2007) 15 Y H Jia, H T Tran, D H Kim, S J Oh, D H Park, R H Zhang, and D H Ahn, “Simultaneous organics removal and bio-electrochemical denitrification in microbial fuel cells,” Bio Bios Eng., 31, 315 (2008) 16 Y Fern´andez-Nava, E Maranon, J Soons, and L Castrill´on, “Denitrification of waste water containing high nitrate and calcium concentrations, Bioresour Technol., 99, 7976 (2008) ă Yăuksel, M Rda, and M Yăuksel, Removal of nitrate from 17 S Samatya, N Kabay, U aqueous solution by nitrate selective ion exchange resins,” React Funct Polym., 66(11), 1206 (2006) 18 C Polatides, M Dortsiou, and G Kyriacou, “Electrochemical removal of nitrate ion from aqueous solution by pulsing potential electrolysis,” Electrochimica Acta, 50, 5237 (2005) 19 L H Zhang, J P Jia, D W Ying, N W Zhu, and Y C Zhu, “Electrochemical effect on denitrification in different microenvironments around anodes and cathodes,” Research in Microbiology, 156, 88 (2005) 20 M S El-Deab, “Electrochemical reduction of nitrate to ammonia at modified gold electrodes,” Electrochimica Acta, 49, 1639 (2004) 21 K Bouzek, M Paidar, A Sadilkova, and H Bergmann, “Electrocatalytic activity of platinum modified polypyrrole films for the methanol oxidation reaction,” J Appl Electrochem., 31, 501 (2001) 22 S Taguchi and J M Feliu, “Kinetic study of nitrate reduction on Pt(110) electrode in perchloric acid solution,” Electrochim Acta, 53, 3626 (2008) 23 J Souza-Garcia, E A Ticianelli, V Climent, and J M Feliu, “Nitrate reduction on Pt single crystals with Pd multilayer,” Electrochim Acta., 54, 2094 (2009) 24 G H Zhao, Y G Zhang, Y Z Lei, B Y Lv, J X Gao, D M Li, and Y N Zhang, “Fabrication and electrochemical treatment application of a novel lead dioxide anode with superhydrophobic surfaces, high oxygen evolution potential, and oxidation capability,” Environ Sci Technol., 44, 1754 (2010) 25 K Tada and K Shimazu, “Kinetic studies of reduction of nitrate ions at Sn-modified Pt electrodes using a quartz crystal microbalance,” Journal of Electroanalytical Chemistry, 577, 303 (2005) 26 J Cao, H Zhao, F Cao, and J Zhang, “The influence of F- doping on the activity of PbO2 film electrodes in oxygen evolution reaction.” Electrochim Acta, 52, 7870 (2007) 27 M H Zhou, Q Z Dai, L C Lei, C Ma, and D H Wang, “Long life modified lead dioxide anode for organic wastewater treatment:Electrochemical characteristics and degradation mechanism.” Environ Sci Technol., 39, 363 (2005) 28 Z MaCova and K Bouzek, “Electrocatalytic activity of copper alloys for NO3 − reduction in a weakly alkaline solution Part 1: Copper–zinc, Department of Inorganic Technology,” Journal of Applied Electrochemistry, 35, 1203 (2005) 29 H L Chen, K F Chen, S-W Lai, Z Dang, and Y P Peng, “Photoelectrochemical oxidation of azo dye and generation of hydrogen via C-N co-doped TiO2 nanotube arrays,” Separation and Purification Technology, 146, 143 (2015) 30 Lele Wang, Miao Li, Chuanping Feng, Weiwu Hu, Guoyu Ding, Nan Chen, and Xiang Liu, “Ti nano electrode fabrication for electrochemical denitrification using Box–Behnken design,” Journal of Electroanalytical Chemistry, 773, 13 (2016) 31 A S Lima, M O Salles, T L Ferreira, T R L C Paixao, and M Bertotti, “Scanning electrochemical microscopy investigation of nitrate reduction at activated copper cathodes in acidic medium,” Electrochim Acta, 78, 446 (2012) 32 A C A de Vooys, M T M Koper, R A van Santen, and J A R van Veen, J Electroanal Chem., 506, 127 (2001) Downloaded on 2017-03-10 to IP 80.82.77.83 address Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract) ... Preparation, characterization and application as nitrate sensor,” Sensors and Actuators B, 20 7, 186 (20 15) G E Dima, A C A de Vooys, and M T M Koper, “Electrocatalytic reduction of nitrate at... nitrite, and ammonia concentrations using an IrO2 anode and a NaCl concentration of 0.3 g/L with current density of 30 mA/cm2 and (B) Temporal changes in nitrate, nitrite, and ammonia concentrations... Cu- Zn- TNTA nanoelectrode (plating Cu: 0.15 A for 10 s, plating Zn 0.15 A for s), and (E) the Cu- Zn- TNTA nanoelectrode (plating Cu: 0.15 A for 10 s, plating Zn 0 .25 A for 10 s) Downloaded on 20 17-03-10