As a pollutant in water resources, nitrate is a target contaminant for removal by water treatment technologies. Therefore, it is necessary to develop new techniques of water treatment to remove nitrate from water resources. This study worked on developing a new technique for nitrate reduction and to produce valuable ()/harmless () products without employing energy-intensive processes. To reach this goal, it is necessary to understand the possibilities and the pathways of nitrate reduction by negatively and positively charged, and hydrophobic peptide-coated Au electrodes. Also, stability and kinetics analysis will help us to understand the durability and capability of peptide-coated Au electrodes for nitrate reduction.
What Did We Do?
In this study three different types of peptides including, hydrophobic (V type), negatively charged (E type), and positively charged (K type) peptides were synthesized. The synthesized peptides were coated on the surface of bare Au. To assess the response of peptide- coated Au electrodes, and to compare them with bare Au, cyclic voltammetry (CV) experiments were employed. To do the CVs, an electrochemical cell with the gold electrode (working electrode), platinum (counter electrode) electrode, and a background solution (0.5 M) were used for electrochemical experiments. As a source of nitrate, 0.1 M sodium nitrate was added to the background solution. Cyclic voltammetry trials were done on three different peptide-coated Au electrodes and bare Au electrode, with a scan rate of 20 mV/s. After CV analysis, and to analyze the products of nitrate reduction, potential hold experiments were done on peptides with promising responses to the CV experiments. In other words, a potential hold experiment with a potential equal to the onset potential of peptide-coated Au electrodes were employed for 1 hour. During the potential hold trials, samples were analyzed using Ultraviolet–visible spectroscopy method in time intervals (e.g., every 10 minutes) to measure the concentration of ammonia and nitrite.
What Have We Learned?
Based on the preliminary results, Au electrodes coated by E and V peptides showed promising responses to the applied potential. Results indicate that reduction of nitrate takes place at the onset potentials of -0.35V and -0.23V versus reversible hydrogen electrode (RHE) for E and V types of peptide-coated Au electrodes, respectively. However, bare Au did not show a reduction peak in the voltammogram. Results of potential hold experiment and product analysis indicate that V and E peptide-coated Au electrodes are capable of nitrate reduction to both nitrite and ammonia. However, bare Au electrode can only reduce nitrate to ammonia.
To have a comprehensive analysis of products, gas chromatography will be used to measure the products (e.g., hydrogen and nitrogen) in gaseous phase. Also, to investigate the structure and stability of thiolate– gold bonding on the surface of Au electrodes, Fourier transform infrared (FTIR) method will be employed before CV, and potential hold experiments. A mass balance between products and nitrate available in the background solution will be done. Moreover, the rate and kinetics of nitrate reduction will be assessed using the product analysis data.
Arash Emdadi, Ph.D. student, Pennsylvania State University
Lauren F. Greenlee, Associated Professor, Pennsylvania State University
Corresponding author email address
Julie Renner, Assistant Professor, Case Western Reserve University; Amir Akbari, Ph.D. student, Pennsylvania State University
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- Phebe H. van Langevelde, Ioannis Katsounaros, Marc T. M. Koper, Electrocatalytic Nitrate Reduction for Sustainable Ammonia Production, Joule, 2021, 5, 290–294. https://doi.org/10.1016/j.joule.2020.12.025
The authors acknowledge funding from the USDA NIFA AFRI Water for Food Production Systems program, grant #2018-68011-28691.
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