Abstract
Here, we investigate the effects of hydrodynamics and temperature on the formation of nitrous and nitric acids (HNO (y=2,3)) and their conjugate bases (NO (y) (-)) in plasma-treated water (PTW) in a surface dielectric barrier discharge (sDBD) reactor. The stirring rate and bulk water temperature were systematically varied from 200 to 1000 rpm and 20 to 80 °C, respectively, while the plasma was held constant. Species in both the gas and liquid phases were tracked in real time using synchronized dual optical absorption spectroscopy, allowing correlation of the gas-phase O(3)/NO (x=1-3) dynamics with the evolving aqueous species of NO(2) (-), HNO(2), and NO(3) (-). Nitrate production monotonically accelerated with increasing agitation and dominated above 800 rpm, whereas the nitrite pool, NO(2) (-) + HNO(2), peaked at a moderate speed of 600 rpm and declined at higher speeds, probably due to volatilization losses. Elevated water temperature suppressed NO and NO(2) formation, extended the O(3)-rich regime, and shifted selectivity toward NO(3) (-); conversely, cooler conditions favored nitrite accumulation. These trends reveal the temperature-dependent kinetics and mass-transfer limits that govern plasma-driven nitrogen fixation. Our findings offer practical guidelines for tuning the composition of PTW, thereby advancing its efficient, application-specific production at scale.