Study On Degradation Of Dye Wastewater By Persulfate Activated By Magnetic Nitrogen Doped Carbon Nanotubes

Dye wastewater is one of the main sources of water pollution,which has high chroma,poor biodegradability and can persist in the environment,which has a great threat to human body and ecological environment.At present,the treatment of dye wastewater is not satisfactory,and the advanced oxidation technology of activated persulfate(PS-AOPs)shows great application potential due to its stable and efficient characteristics.However,there are still many shortcomings in the current catalytic materials for activating persulfate,so it is very important to develop green,efficient and sustainable new catalytic materials.In this paper,magnetic N-doped carbon nanotube heterogeneous composite catalyst Fe⁰@N-CNTs/Fe₃O₄ was successfully synthesized by a simple pyrolysis method using C₆H₁₂O₆,CH₄N₂O and Fe(NO₃)₃·9H₂O as carbon source,nitrogen source and metal iron source,respectively.Taking typical refractory organic dye methyl orange(MO)as the target pollutant,three researches on catalyst preparation,catalytic performance and catalytic mechanism have been carried out.The main research contents and results are listed as follows:(1)A series of heterogeneous composite catalysts were prepared by a simple pyrolysis method,and the catalyst activated PDS oxidation degradation system was constructed.Taking the removal rate of MO as the investigation target,the optimal raw material ratio and calcination temperature of catalyst preparation were determined.When the molar ratio of C₆H₁₂O₆,CH₄N₂O and Fe(NO₃)₃·9H₂O was 1:30:1,and the temperature was 800?in N₂ atmosphere,the catalytic performance was the best.TEM,XRD,XPS and other characterization tests showed that the catalyst under optimal preparation conditions was a structure of nitrogen-doped carbon nanotubes coated with Fe⁰ and supported Fe₃O₄ on the outer surface(Fe⁰@N-CNTs/Fe₃O₄).The coated Fe⁰ and supported Fe₃O₄ contributed to the catalyst with good magnetic properties.(2)In Fe⁰@N-CNTs/Fe₃O₄/PDS system,the effects of PDS dosage,catalyst dosage and initial p H of solution on the degradation efficiency of MO were discussed.The optimum reaction conditions were determined as follows:PDS and catalyst dosage were200 mg/L,and the initial p H of solution was 5.87.At the same time,the system also had good degradation performance for other types of dyes(MB,TY,etc.),and the common interfering ions Cl^-had little effect on the catalytic performance.In addition,the cycling experiment and iron ion dissolution experiment of the catalyst show that the catalyst has good stability.Therefore,the catalyst is an efficient,green and sustainable material with great application potential.(3)Through the analysis of different reaction systems,PDS consumption curves,free radical and non-free radical quenching experiments,it is shown that Fe⁰@N-CNTs/Fe₃O₄/PDS reaction system will produce SO₄^-???OH and ¹O₂ active substances,of which ¹O₂ plays a major role.Combining with XPS,FTIR and other characterization test methods,the main active sites in the reaction process were identified as Fe⁰ loaded on the catalyst,oxygen-containing functional groups(carboxyl,hydroxyl,etc.)on the surface of carbon materials,nitrogen-containing groups(pyridine-type N and graphite-type N,etc.)introduced by nitrogen doping,surface defect structure of carbon nanotubes and delocalized?electrons,etc.Then the reaction mechanism of the system was speculated.