Enhanced production of hydroxyl radical in water treated by negatively biased microwave plasma

Abstract

Hydroxyl radical (OH•) in plasma-treated water (PTW) has a high oxidation capability that is useful for many practical applications such as disinfection and decomposition of organic pollutants in wastewater. The short lifetime of OH• makes it desirable compared to other oxidative chemicals that remain in solutions after use. This thesis provides an in-depth study of maximizing OH• generation in water using an atmospheric pressure microwave plasma coupled with a direct current (DC). The chemical dosimetry showed that the DC biased microwave plasma increased the amount of reacted OH• by two orders of magnitude compared to the case with microwave plasma only. Different concentrations of hydrogen peroxide (H2O2) in water were also tested with microwave plasma only for H2O2 is well known to assist the production of OH• in water. The highest OH• production was found near 0.1 M of H2O2, producing about three times more than the case without H2O2. It is found that H2O2 acts as OH• scavenger with a concentration larger than 0.1 M, resulting in less production of OH•.