Research Of Plasma Discharge Combined With MWCNTs/TiO₂/Fe₃O₄ Materials For Dye Degradation In Printing And Dyeing Wastewater

Rapid industrialization and population growth are driving human demand for clean water.However,with the rapid development of petrochemical,paper,printing,dyeing and other industries in recent years,the number of discharges of various wastewater with complex structures and hard-to-degrade organic pollutants has increased dramatically.Azo dyes,as the main source of printing and dyeing wastewater,pose a serious threat to human physical and mental health because of their complex chemical structures and toxic decomposition products,which are carcinogenic,harmful and resistant to biodegradation.Therefore,the development of efficient organic wastewater treatment technology is of great scientific and practical significance for environmental protection.At present,traditional industrial printing and dyeing wastewater treatment technology has many disadvantages such as high cost,long running time and low separation efficiency,while non-thermal plasma treatment,as a new energy-saving and environmentally friendly water treatment technology,is a potential alternative to improve oxidation processes and has been widely used for the removal of organic pollutants,especially for the decolorization of textile dye wastewater.However,the problem of low energy efficiency of the reaction system of this technology still limits its development.Based on this,the effective catalyst combined with low-temperature plasma technology is proposed to solve the problems by reduced energy consumption and enhanced pollutant degradation.This thesis proposes to use titanium dioxide composite magnetic carbon nanotubes（MWCNTs/TiO₂/Fe₃O₄）with active material catalytic effect as a composite catalyst,which can improve the adsorption catalytic performance and realize magnetic recycle.The effect of MWCNTs and Fe₃O₄can compensate for the TiO₂’s defects like own wide band gap,high composite rate of photogenerated carriers and easy agglomeration.On the other hand,the"pseudo-photocatalytic"behavior of the composite catalyst is activated by the discharge plasma to sublimate the single-acting catalyst into multi-effect catalyst.The details and results of the study are as follows:（1）Based on the convenience of chemical deposition and thermal treatment,Fe₃O₄nanoparticles were loaded on the purified MWCNTs-COOH as the basic backbone to produce magnetic Fe₃O₄/MWCNTs,and then TiO₂nanoparticles with photocatalytic efficiency were grafted on the surface by（3-aminopropyl）triethoxysilane to obtain an improved Fe₃O₄-TiO₂/MWCNTs composite photocatalyst based on the original one.The improved Fe₃O₄-TiO₂/MWCNTs composite photocatalyst was obtained by grafting TiO₂nanoparticles with photocatalytic efficiency on the surface of（3-aminopropyltriethoxysilane）to obtain an improved Fe₃O₄-TiO₂/MWCNTs composite photocatalyst.The feasibility of the modification was confirmed by XRD,SEM,TEM and FTIR test characterization.In addition,the decolorization performance of MWCNTs/TiO₂/Fe₃O₄for MB was investigated.The experimental results showed that the catalyst adsorbed methylene blue（MB）dye,and the decolorization rate reached 75.6%when the catalyst dosage was 3.0 g/L,and the activity of the catalyst gradually increased with the increase of the catalyst dosage.The decolorization rate was negatively correlated with the dye concentration.The solution pH had a certain degree of influence on the removal of MB,and the decolorization rate of MB had a good decolorization rate under neutral conditions.（2）The effects of discharge time,input voltage,initial concentration of dye and initial pH value in the discharge system on the effect of non-thermal plasma degradation of methylene blue simulated printing and dyeing wastewater were systematically investigated to explore the feasibility of its degradation of printing and dyeing wastewater.When the discharge voltage was 24 k V,the initial concentration of MB C₀=100 mg/L and the initial pH of the solution=6.8,the decolorization rate reached93.8%after 60 min of treatment.The experimental results showed that with the increase of DBD discharge time and input voltage,the degradation rate of MB showed a change of increasing first and then stabilizing.In addition,the degradation rate of MB showed a decreasing trend with the increase of the initial concentration of MB,and the above degradation reactions all followed the first-order kinetic law;neutral and alkaline environments were more favorable for DBD to degrade MB solution,and it was found that the pH value showed a decreasing trend during the degradation of DBD MB,which was maintained at 2.89～3.11.In addition,the combination of catalyst and DBD discharge system could play an enhanced role,and the degradation efficiency of MB reached 95.6%after 60 min treatment under the same parameters,which was 25.6%higher than that of DBD alone.At the same time,the mineralization rate of the solution could be increased from 4.35%to 35.46%;the increase of the mineralization rate of the solution was mainly due to the increase of the yield and utilization rate of the active particles by the catalyst combined with the discharge system.In summary,the combined MWCNTs/TiO₂/Fe₃O₄discharge system can enhance the degradation rate of printing and dyeing wastewater compared with the separate discharge system,and has excellent magnetic separation performance to facilitate the recycling of the catalyst.It is believed that the study will provide new ideas for the effective treatment of printing and dyeing wastewater.