Electrochemical Reduction Nitrate In Water On Modified Copper Electrodes

The increasing nitrate concentration in ground and surface water have been became a global problem and the EPA limited the maximum nitrate permitted concentration in drinking water was 10mg/L (calculated by NO3--N). In general, the nitrate removal method include bio-denitrification, chemical reduction, electrochemical methods and physical-chemical methods and of these methods, electrochemical reduction method has been proven to be an effective method with low energy resume and have been investigated by many researchers. Copper is an available cathode material for nitrate reduction and the modified copper electrodes with deposited a copper film at different substrates could improve the surface area of electrodes and nitrate reduction efficiency. However, the rapid oxidation of copper during nitrate reduction limited these electrodes in long time reaction.In this paper, we proposed a new method for improving the copper electrodes stability and activity by modifying the copper material with annealing treatment. First, we compared the deposited Cu and bare Cu in nitrate reduction and found the deposition of a copper film could improve the nitrate reduction efficiencies. Subsequently, we used the annealed Cu/Ni electrodes for nitrate reduction and found this electrode could reduce nitrate more efficiency than deposited Cu electrodes at the range of -0.8 V～-2.0 V. With the test of LSV curve, we found the annealed Cu/Ni electrode showed a ca.20%～50% higher peak current of nitrate reduction and a ca.250mV positive shift of the peak potential than that of deposited Cu and bare Cu electrodes, respectively. It demonstrated that more catalysis active sites have been built at the surface of annealed Cu/Ni electrodes. The optimal preparation of annealed Cu/Ni electrodes were also investigated and we found the electrodes prepared by annealing the 10 min deposited Cu/Ni electrodes for 0.25 h at 300 ℃ lead to the highest nitrate removal efficiency. The characterization test showed the presence of nano-wire and nanoparticle on the Cu/Ni electrodes with annealing treatment, which provided more surface area and reactive for nitrate reduction.Subsequently, we investigated the Cu-Ni alloy (Cu-Ni10, Cu-Ni20, Cu-Ni30) for nitrate reduction at different potential and found all of the three alloy did not have the higher nitrate removal efficiency than bare Cu electrodes, which suggested the Cu-Ni alloy materials did not have a good selective for nitrate reduction. However, if we modifying the Cu-Ni alloy with high temperature treatment, the nitrate removal efficiency could improve as high as deposited Cu electrodes and these annealed Cu-Ni alloy could keep stable after annealing treatment.In this paper, we found the production of nitrate reduction on different Cu electrodes were ammonia and nitrite. As with the annealed Cu/Ni employed as cathode, the highest nitrate removal efficiency could be obtained, we investigated the stability of annealed Cu/Ni during a 48 h nitrate reduction experiment and suggested rate and Faradaic efficiency of nitrate reduction on Cu/Ni electrodes could remain stable. The electrodes were also employed for the determination of nitrate in water and the results showed a linear response was obtained in the 4.98 mg/L-90.9 mg/L NO3--N.