Synergistic degradation of aqueous p-nitrophenol using DBD plasma combined with ZnO photocatalyst

Abstract

In this study a dielectric barrier discharge non-thermal plasma (DBD-NTP) reactor was combined with ZnO nanoparticles to degrade p-nitrophenol (PNP) in aqueous solution. When the plasma process was combined with ZnO nanoparticles an obvious improvement was obtained in PNP removal efficiency. this was seemingly due to activation of ZnO photocatalysts under the UV light produced in discharge region. The results showed that addition of the optimum amount of ZnO nanoparticles (250 mg/L) to the plasma reactor could increase the removal efficiency from 49 % to 91 %, whereas the UV/ZnO photocatalytic process alone only lead to 12 % PNP removal. This is indicative of the synergistic enhancement of PNP degradation efficiency in the combined NTP-ZnO process rather than simply an additive effect. The effects of intial solution pH, applied voltage, and initial PNP concentration were also investigated on the sole NTP and NTP-ZnO processes in terms of removal efficiency. Alkaline solution conditions, and lower initial PNP concentration favored both processes, while the applied voltage of 13 kV yielded the optimum PNP removal. Furthermore, higher total organic carbon (TOC) removal and higher kinetic constant of PNP degradation was achieved in the plasma system coupled with ZnO photocatalysis. Energy consumption analysis revealed that the NTP-ZnO process is 4.25 times more energy efficient than the sole plasma process which could be a major step towards industrial utilization of plasma treatment technologies.