Study On The Removal Of Dibutyl Phthalate From Aqueous Solution By Magnetic Carbon Nanotubes

Dibutyl phthalate?DBP?is a kind of phthalate ester endocrine disruptor,which is widely used in synthetic organic compounds.It is easy to penetrate into the outside environment in the process of production and use.DBP with different degree of pollution has been detected in many environmental water bodies.Moreover,DBP is not easy to degrade but easy to enrich in the external environment,and it is difficult to remove in the conventional water treatment process.In this paper,the magnetic MWCNTs were prepared by chemical coprecipitation method using multi-walled carbon nanotubes?MWCNTs?as raw materials.The magnetic MWCNTs were used to remove dibutyl phthalate from water,and the structural characteristics of magnetic MWCNTs were analyzed by characterization.The adsorption properties of DBP by magnetic MWCNTs were systematically investigated.The kinetics and thermodynamics of the adsorption of DBP by magnetic MWCNTs were researched.The microwave regeneration of the magnetic MWCNTs adsorbing DBP was studied and the regeneration mechanism was discussed.The role of magnetic iron oxides in regeneration was discussed.The preparation conditions of magnetic MWCNTs were optimized,and the primary and secondary order of the factors affecting the removal of DBP was determined as follows:reaction temperature,stirring speed,reaction time and mass ratio of MWCNTs/Fe₃O₄.The optimum preparation conditions were as follows:reaction temperature was at 60?,stirring speed was at 400rpm,reaction time was at 45min,mass ratio of MWCNTs/Fe₃O₄ was 2:1.The removal rate of DBP by magnetic MWCNTs was98.56%in 30 min with the initial DBP concentration of 10mg/L,the magnetic MWCNTs dosage was 0.2g/L,and the stiring speed was 200 r/min.The magnetic MWCNTs was characterized by scanning electron microscopy?SEM?,Fourier transform infrared spectroscopy?FTIR?,specific surface area and pore size analysis?BET?,and the magnetic MWCNTs dynamic fluid recovery experiments showed that the magnetic MWCNTs had good magnetic properties with the magnetic iron oxides loaded on the MWCNTs successfully,with which the specific surface area,the pore volume and the average pore size of the magnetic MWCNTs were 301.16m²/g,0.7743cm³/g and10.28nm.The effects of magnetic MWCNTs dosage,initial DBP concentration,reaction time,reaction temperature,solution pH,ionic strength,and coexistent humic acid on the removal efficiency of DBP were studied.The results showed that the removal rate of DBP increased gradually as the dosage of magnetic MWCNTs increased,but after the dosage increased to 0.2 g/L,the removal rate increased little and gradually stabilized.When the initial concentration of DBP exceeded 5 mg/L,the DBP removal rate decreased as the DBP initial concentration increased,while the adsorption amount increased.During the adsorption in the early 5 min,the magnetic MWCNTs adsorbed DBP faster,then increased slowly and reached adsorption equilibrium after 7 hours.The equilibrium adsorption capacity was 49.6955 mg/g in DBP initial concentration of 10 mg/L.The decrease of temperature contributed to the adsorption of DBP by magnetic MWCNTs.Na⁺and Mg²⁺in low concentration inhibited the adsorption of DBP to a certain degree,but the DBP removal rate increased slightly with the increase of metal ion concentration.The two factors of pH and coexisting humic acid had no obvious effect on the DBP removal rate.The results obtained from the comparative study on the removal efficiency of five kinds of PAEs?DMP,DEP,DBP,BBP,and DOP?showed that the magnetic MWCNTs had better adsorption on the hydrophobic DBP,BBP and DOP.The kinetics and isotherms of DBP adsorption by magnetic MWCNTs were studied.The results showed that the pseudo-second-order kinetic model and Freundlich adsorption isotherms could better reflect the DBP adsorption process on magnetic MWCNTs.The thermodynamics studies showed that enthalpy value?H⁰?was found to be 91.9219 KJ·mol^-1,the entropy value?S⁰?was found to be 188.8691 J·mol^-1·K^-1,and the free energy change?G⁰?was found to be negative.Those indicated that the adsorption process was an exothermic process,physical and chemical adsorption all existed in the adsorption process,but chemical adsorption was main.The dominant mechanism in adsorption is hydrophobic interaction and?-?interaction.The thesis studied the effects of microwave power,microwave time and concentration of regenerated powder on regeneration,the effect of recycling adsorption-regeneration times on the adsorption properties of magnetic MWCNTs.The results showed that the regeneration rate increased with the increase of microwave irradiation time and microwave power,The regeneration rate in low powder concentration increased firstly and then decreased a little with the prolongation of microwave irradiation time,while the regeneration rate in high powder concentration increased firstly and then tended to be stable,and the regeneration rate was kept above 100%.The optimum regeneration process conditions were that microwave power and time was 600 W and 20min,respectively,powder amount was 3 g,solvent water volume was 30 ml.At this condition,the regeneration rate of magnetic MWCNTs was 102.64%.After five cycles of magnetic MWCNTs regeneration,the adsorbent adsorption properties and magnetic properties were kept good.During the microwave regeneration,the“hot spots”generated on the carbon nanotubes,which could burn and oxidize DBP to degrade,thus the magnetic MWCNTs achieved effective regeneration.