The Application And Mechanism Research Of Non-Thermal Plasma-Catalysts System For Synergistic Degradation Of Organic Pollutants

With the rapid development of industrialization and the large-scale use of chemicals,global environmental pollutions caused by organic contaminants are becoming more and more serious.These organic pollutants can be discharged into the atmospheric environment in the form of volatile organic compounds(VOCs),or directly released into the water environment.The vast release of organic contaminants not only seriously endangers human health,but also damage the ecological environment.Non-thermal plasma(NTP)has been widely applied for the treatments of organic contaminants due to its high catalytic reactivity,non-additional chemicals and minimal environmental impact.Highly active environment composed with energic electrons and radical specious in NTP reactor contributes to the degradation of organic materials.However,the diversity of the functional radical specious and multiple degradation pathway determines the low energy utilization efficiency,low degradation selectivity and substantial emission of byproducts.The cooperative combination of NTP and catalysts can address the aforementioned limits.A higher degradation efficiency for the organic compounds can be realized under a lower discharge power by using the synergy between NTP and catalysts.The binding modes of NTP-catalyst system can be divided into three kinds according to the location of catalysts.In plasma catalyst(IPC)and post plasma catalyst system(PPC)are used for VOCs treatments,a third form is the catalytic ozonation which based on the NTP generated ozone,catalytic ozonation have been widely studied for water purification.Obviously,the design and preparation of catalysts play an essential role in plasma-catalyst system.This work paves the lights to design suitable catalysts for plasma-catalyst system based on their respective characteristics,and systematically investigated the synergistic principles.The specific works are as the follows:1.For IPC modes,a novel graphene oxide(GO)-BiOCl(001)nanocomposite was prepared and applied in NTP system for the degradation of acetone.It is found that the selective crystal orientation deposition of BiOCl(001)on GO can greatly enhance the oxidation rate to 89.94%.Under the excitation of energic electrons generated by NTP,the“photocatalysis-like”behavior occurs on the surface of the GO-BiOCl(001)play a crucial role in the IPC modes.Three effects contribute to this high catalytic activity of GO-BiOCl(001)sample:(1)BiOCl nanosheets boots strong attenuation capability for high energy electrons due to the element sensitizing strategy of high atomic number elements(Bi);(2)GO works as a bridge to accelerate the migration of excited electrons and reduce the quenching probability of generated electron-hole pairs;(3)The interface design of GO-BiOCl(001)ensures the maximum electron transfer kinetics by increasing the transfer rate and shortening the migration distance.2.For PPC modes,an advanced low-oxygen-pressure calcination process is developed to fine-tune the oxygen vacancy(Vo)concentration of MOF-derived TiO₂nanocrystals.Vo-poor and Vo-rich TiO₂ catalysts were placed in the back of a non-thermal plasma(NTP)reactor to convert harmful ozone molecules into ROS that decompose VOCs via heterogeneous catalytic ozonation processes.The results indicate that the Vo-TiO₂-5/NTP with the highest Vo concentration exhibited superior catalytic activity in the degradation of toluene,achieving maximum 96%elimination efficiency and 76%CO_x selectivity at an SIE of 540 J/L.Mechanistic analysis reveals that the ~1O₂,O₂^-and?OH species derived from the activation of O₃ molecules on Vo sites contribute to the decomposition of toluene over the Vo-rich TiO₂ surface.The roles of Vo in manipulating the synergistic capability of post-NTP systems were attributed to increased O₃ adsorption ability and enhanced charge transfer dynamics.3.For catalytic ozonation which applied for water treatments,a facet-engineered Mn₃O₄ catalysts with abundant oxygen vacancy was prepared and used in plasma-catalysts system for the degradation of Bisphenol A(BPA)in aqueous environment.Firstly,amino acids of varying chain lengths were used as template reagents to prepare an array of defect-rich Mn-BTC via pre-occupation and steric hindrance effects.The increase of amino acid's chain lengths not only increased the defect concentration of the prepared Mn-BTC,but also changed the morphology from typical rod-like to spherical/flower shape.After the subsequent calcination treatments,a serious of Mn₃O₄catalysts with different oxygen vacancy concentration was obtained.Interestingly,the introduction of amino acid also changed the exposed crystallographic facets from(101)to(211).When combined with NTP generated ozone molecule,Mn₃O₄-VAL exhibited the excellent ozone activation capacity,BPA degradation reaction was completed in 40min.The radical quenching experiments and EPR spectrum indicated that ~1O₂ and·OH were the main species for BPA elimination.The higher catalytic activity of Mn₃O₄-VAL was attributed to the exposure of active facets and the increased oxygen vacancy concentration.4.For catalytic ozonation modes which applied for water treatments,a single-layered graphene film(GF)was developed and used as the plasma catalysts for Sulfamethoxazole(SMZ)degradation in water conditions.Graphene-based catalysts can avoid the leaching of metal ions which is particularly prevalent in metal catalysts.Nowadays,graphene-based catalysts have been widely used as the substitutes for metal catalysts.However,as difficult to obtain graphene with high structural precision,it is currently unfeasible to comprehend the relationships between intrinsic structure of the layered carbon catalysts with its catalytic activities.Here,an advanced plasma-assisted etch strategy was used to fine-tune the ozonation activity of mono-layered graphene films by tailoring the defect types.Raman mapping indicated that the defects of the as-prepared mono-layered graphene films were predominantly sp~3,vacancy and boundary type defects,respectively.The roles and contributions of these active defects in manipulating the oxidative potential of mono-layered graphene films were revealed by quenching experiments,electron paramagnetic resonance results and density functional theory calculations.The catalytic results showed that the mono-layered graphene films with boundary-like defects exhibited the best catalytic performance towards the degradation of SMZ.This work contributes new insight into the design of high efficiency carbonaceous catalysts by structuring additional defective sites.