Study On Degradation Of PNP In Water With Enhanced Dielectric Barrier Discharge Plasma By Mn Fe₂O₄

Advanced oxidation processes?AOPs?have been considered effective and rapid approaches to remove refractory organic pollutants from wastewater.Dielectric barrier discharge?DBD?as a promising advanced oxidation processes?AOPs?can generate not only oxidizing species such as short-lived radicals?·OH,etc.?,and long-lived molecules?H₂O₂,etc.?,but also physical effects?UV-visible light and shockwaves,etc.?,which can react with the organic pollutants.Due to the high efficiency and no second pollution,DBD has been widely used as an effective method for treatment of refractory organics in wastewater.However,the incomplete utilization of active species such as H₂O₂ and UVvisible light has reduced the energy efficiency of discharge plasma.Mn Fe₂O₄ has high catalytic activity and excellent photochemical stability.In this study,Mn Fe₂O₄ was combined with DBD plasma in a coaxial cylindrical structure,which can activate the plasma-generated H₂O₂ and exploit UV-visible light to generate more active species toward PNP degradation in water.Mn Fe₂O₄ nanoparticles were synthesized by co-precipitation and hydrothermal methods,respectively.It was found that the catalytic activity of the sample synthesized by co-precipitation was better than the other samples.The synthesized Mn Fe₂O₄ by coprecipitation method was characterized using SEM,EDS,XRD,XPS and UV-vis-DRS.The results showed that the catalyst was match well with cubic spinel structure of Mn Fe₂O₄ and revealed Mn Fe₂O₄ nanoparticles was spherical shape with Fe,O,and Mn.Furthermore,the light absorption range of Mn Fe₂O₄ exhibited greater than 400 nm and the portion of Fe³⁺and Mn²⁺ on the surface of used Mn Fe₂O₄ was transformed to Fe²⁺ and Mn³⁺,indicating that Fe²⁺/Fe³⁺and Mn²⁺/Mn³⁺species were involved in activation in the Mn Fe₂O₄/DBD system.The performance of p-nitrophenol?PNP?degradation in water by Mn Fe₂O₄/DBD plasma system was studied.After 15 min treatment time,the highest degradation efficiency can reach 91.6% under the experimental conditions: initial PNP concentration of 10 mg/L;applied voltage of 18 k V;solution circulation rate of 300 m L/min and the addition of 2 g/L Mn Fe₂O₄,respectively.Correspondingly,the kinetic constant and yield were 5.2 times and 2.4 times higher than that in sole DBD system,respectively.Furthermore,compared to sole DBD system,addition of Mn Fe₂O₄ can further improved the PNP removal efficiency at initial p H ranged from 3 to 11 and the effect of the solution circulation rate on degradation efficiency of PNP was decreased with Mn Fe₂O₄ indicating that the Mn Fe₂O₄ /DBD plasma system has the potential to treat high velocity wastewater.In addition,Mn Fe₂O₄ exhibited stable reusability after cyclic batch experiments.The reaction mechanism of Mn Fe₂O₄/DBD plasma system and the degradation mechanism of PNP were analyzed.The catalysis mechanism was explored by the plasmagenerated H₂O₂ concentration quantitative test,XPS spectra of Mn Fe₂O₄ before and after the reaction and the UV-vis-DRS of Mn Fe₂O₄.It indicated that plasma-generated H₂O₂ can be activated by Mn Fe₂O₄ and Mn Fe₂O₄ can exploit both UV light and visible light generated by DBD in water.During the DBD,activation of plasma-generated H₂O₂,photocatalysis process,active species such as ·OH,·O₂^-and h⁺ were generated,which may be attributed to the PNP degradation.In addition,DFT computation has been performed using Materials Studio program package.The geometry optimizations were performed with B3 LYP functional and the Mulliken Population analysis and Fukui Function were used to analyse and predict the possible degradation pathways of PNP.Finally,the toxicity estimation software tool?T.E.S.T.?was used to predict the toxicity of PNP and possible intermediate products,it is illustrated that the Mn Fe₂O₄/DBD plasma system can reduce the toxicity of PNP in water.