Preparation Of Boron And Nitrogen Doped Carbon Nanotubes And Study On Degradation Of Phenol In Water

Persulfate advanced oxidation technology is a technology that uses activated persulfate to generate strong oxidizing sulfate radicals to degrade organic pollutants.Nevertheless,the dissolution of toxic metals on the catalyst can easily cause secondary pollution.Consequently,the development of environmentally friendly and excellent effects Carbon material activated persulfate technology has become the only way for green development.This article intends to use carbon nanotubes with sp² structure as the basis of a new type of non-metallic catalyst,and improve its catalytic activity through the doping of boron and nitrogen to produce defective surfaces.Based on the investigation of the catalyst's substitution efficiency for heavy metal cobalt,the degree of influence of various preparation conditions and reaction conditions on the degradation of pollutants by non-metallic catalysts was extracted.Through in-depth analysis of the changes in the catalyst structure,active species and dominant reaction types before and after doping,the efficient mechanism of the catalyst is clarified.The research in this article has important scientific significance and potential application value for the development and improvement of green and high-efficiency new water treatment technologies.The specific research content is as follows:Preparation of defective sp² carbon catalyst:change the type of carbon nanotubes,the content of doping elements and the modification conditions,and prepare a series of modified carbon catalysts for comparison;Catalyst activated persulfate to degrade pollutants:examine the removal rate and removal rate of phenol,and screen out the best catalyst composition,best test conditions and best removal effect;Analyze the degradation products qualitatively and quantitatively,grasp the types and distribution of the products,investigate the active species and reaction types that play a role in the degradation process,and preliminarily infer the reaction mechanism;The mechanism of the reaction system:comprehensively characterize the catalyst,combine the active species in the reaction system,and explore the type of reaction and the degradation mechanism of phenol by the carbon catalyst.The research conclusions are as follows:1.With carbon nanotubes as the carrier,the electron-deficient boron atom-doped catalyst(B-MWNT)and the electron-rich nitrogen atom-doped catalyst(N-MWNT)are obtained through the three processes of acidification,dispersion and calcination.The calcining method can fully evaporate the dispersant ethanol to dryness,increase the contact area of heteroatoms and carbon nanotubes,and become an excellent preparation method.Acidification with concentrated nitric acid,multi-walled carbon nanotubes(MWNT),boric acid/melamine,a small amount of precursor,800?annealing temperature and ultrapure water washing to neutrality are the most suitable preparation conditions for boron(B)/nitrogen(N)doping.2.The catalytic activity of the catalyst largely depends on the degree of defects.This article adjusts its effect by acidification and the amount of heteroatom doping.Under the optimal conditions,the removal rates of phenol by the catalysts MWNT,B-MWNT and N-MWNT were 14.1%,91.4%and 95.9%,respectively,within 20 minutes.The doping of B and N can improve the catalytic activity of carbon nanotubes.Nonetheless,the doping amount of N atoms is high,and the catalytic activity of the carbon catalyst can be improved only when the doping level of B is low.The activated permonosulfate(PMS)degrades organic pollutants,and the Raman results show that the carbon is doped with boron atoms.The degree of defects of nanotubes increases,but the doping of nitrogen atoms reduces the degree of defects.3.Analysis by SEM,TEM and XRD proves that heteroatom doping will not change the internal and external structure of carbon nanotubes,and will not damage its sp² structure.XPS characterization results show that B exists in three forms:C₃B,CBO₂ and CBO₃.N exists in the form of pyridine nitrogen,pyrrole nitrogen and graphitic nitrogen.The catalytic activity of the catalyst doped with N is more dependent on the exposed graphite with the sawtooth edge nitrogen.EPR and quenching experiments show that free radicals(?OH?SO₄^-·?O₂^-·)and non-radicals(¹O₂)exist in both systems,and the dual reaction pathways degrade phenol together.4.In the N-MWNT/PMS system,non-radicals play a leading role,while in the B-MWNT/PMS system,free radicals are the main degradation means.In the non-radical pathway,in-situ Raman characterization knows that,The new substance B-MWNT-PMS*is produced in the degradation system.The catalyst B-MWNT acts as an electronic conductor in the B-MWNT/PMS system,accelerating the transfer of electrons from electron-rich organics to PMS,while the catalyst N-MWNT itself is rich in electrons,so in the B-MWNT/PMS system,it can both Acting as an electronic conductor,it can also provide electronically activated PMS.Both catalysts can be reused 5-6 times,and have good applicability to ambient temperature,acidity and alkalinity,types of oxidants and different pollutants.