Nanowire-based Cu electrode as electrochemical sensor for detection of nitrate in water

Cu electrodes are prepared by thermal annealing of Cu nanowires under Ar atmosphere at 600-800 °C for 30 min. Investigation of as-prepared electrodes by both X-ray diffractometry and scanning electron microscopy indicates that after annealing a rise in the size of Cu nanowires occurs due to the melting of some small-sized Cu nanowires. When the annealing temperature is not too high (e.g. 600 °C), the melting of small-sized nanowires may create many tightly-connected junctions among big-sized nanowires, leading to the formation of a stable, porous nanowire network. The measurements of both electrochemical active surface areas and electrocatalytic activity of these Cu electrodes demonstrate that their active surface areas decrease with increasing the annealing temperature and the electrode prepared at 600 °C shows the highest activity for reduction of nitrate in acidic medium. Examination of the electrode prepared at 600 °C as nitrate sensor via differential pulse voltammetry reveals that this sensor exhibits excellent performance: a linear response ranging from 8 to 5860 μM (R2 = 0.999), a sensitivity of 1.375 μA/μM, and a detection limit of 1.35 μM at a signal-to-noise ratio of 3. Compared with the Cu-based sensors reported in the literature, this nanowire-based sensor not only possesses the broadest linear range but also has a very low detection limit. Its stability, anti-interference ability, and application to nitrate detection in real samples are also investigated.