Continuous Production of High-Concentration Nitrated Water with Catalytic Concentrated High-Intensity Electric Field Process at Ambient Conditions

Considering the potential environmental issues caused by the Haber–Bosch nitrogen fixation process, developing green technology for nitrogen fixation has become a heated topic. In this work, a modified “concentrated high-intensity electric field” (CHIEF) non-thermal plasma system was developed, by combining photocatalysis and electrodialysis for the continuous production of high-concentration nitrated water using air and water. The main system design factors, including: voltage, duty cycle, gas flow rate, N₂/O₂ ratio, and reactor parameters, show significant impacts on the nitrogen fixation, and the composition in the resulting nitrated water. Under high voltage in the CHIEF system, N₂ and O₂ were excited, and generated various reactive nitrogen and oxygen species, resulting in the in-situ reaction with water. These reactions led to the formation of NH₄⁺, NO₂⁻ and NO₃⁻ (ammonium, nitrite, and nitrate ions) in the solution via a series of reactions in the gas phase, gas–liquid interface, and liquid phase. Due to the rapid in situ reaction, the highest nitrogen species yield rate reached 48.28 μmol/min, which was much higher than other reports. The best (least) energy consumption was 23.5 MJ/mol of Nitrogen. In addition, photocatalysis mediated by TiO₂ under UV exposure, greatly promoted the conversion of nitrite to nitrate, because of the generation of ·OH and ·O₂⁻ species. Furthermore, the electrodialysis concentration was able to efficiently decrease the conductivity in the CHIEF system, and enriched the nitrate concentration over dozens of times. This enabled the CHIEF system to continuously achieve high-level nitrogen fixation in an efficient manner.