Understanding the formation of nitrate from nitrogen at the interface of gas–water microbubbles

Abstract

Water microbubbles containing Fe²⁺ ions have been found to efficiently transform nitrogen (N₂) to nitrate (NO₃⁻) by initiating Fenton's reaction at the gas–water interface. Herein, we elucidate the mechanism of the formation of nitrate (NO₃⁻) from nitrogen (N₂) at the microbubble interface. Several experimental studies were conducted to identify the intermediates formed during the conversion. Our investigation shows the formation of H₂N₂O₂, NO, NO₂, and NO₂⁻ intermediates before yielding NO₃⁻ as the final product. Density functional theory (DFT) calculations provide additional support to our observation by providing insights into the energy profiles of the reaction intermediates. We believe that this work not only provides valuable insight into the abiotic nitrogen fixation in microbubbles but also helps in suggesting the modification of parameters to create a more reactive interface that leads to the enhanced production of nitric acid (HNO₃).