Degradation of ferulic acid and caffeic acid by dielectric barrier discharge plasma combined with Mn/CoOOH/activated carbon fiber

Abstract

Organic pollutants of olive mill wastewater (OMW) have caused various negative effect to water environments. It is imperative to develop an effective technology for eliminating organic pollutants in OMW. In this study, representative organic pollutants in OWM, ferulic acid (FA) and caffeic acid (CA), were removed from water by dielectric barrier discharge (DBD) plasma and Mn/CoOOH/activated carbon fiber (ACF) catalyst. The treatment performance and catalytic mechanisms were studied. The results show that the combined system could effectively remove FA and CA. For example, FA and CA degradation efficiency was 81.6% and 94.2% in the 20 L of mixed wastewater with the 100 min treatment using DBD combined with Mn/CoOOH/ACF. Experiments and density functional theory (DFT) calculations indicate that the electron transfer from the catalyst to antibonding orbits of O3 and H2O2 caused the dissociated adsorption, promoting the transformation of O3 and H2O2 to ·O, singlet oxygen and ·OH. Additionally, the doping of Mn in CoOOH benefited the electron transfer because Mn had a higher d-band center than Co in Mn/CoOOH, which was conducive to the interaction of O3 and H2O2 with the catalyst. The possible degradation pathways of FA and CA were proposed.