Preparation Of Acrylic Acid-modified Carbon Nanotubes And Study On The Dye Adsorption Performance Of The Composite Film

With the application of organic dyes in more and more industries,the discharge of dye wastewater is also increasingly severe,which has caused serious harm to the environment and daily life.Adsorption is considered to be the most attractive method in dye treatment.Polyvinylidene fluoride（PVDF）membrane has excellent membrane basic properties,and the large surface area of the membrane can provide a large number of attachment points for the dye,which can remove pollutants quickly.Therefore,it is a kind of adsorption material with potential application value.However,the hydrophobicity of PVDF membrane is easy to cause membrane pollution,which leads to the decrease of membrane efficiency,so we need to modify PVDF membrane.We choose multiwalled carbon nanotubes（MWCNTs）with excellent thermal,mechanical and adsorption properties as the ideal inorganic nano filler to modify PVDF membrane.However,the strong hydrophobicity of MWCNTs resulted in poor dispersion during the preparation of the composite membrane.This paper studied these problems and achieved some results.In this study,acrylic acid（AA）was grafted onto MWCNTs surface by in-situ polymerization,and then AA was polymerized to polyacrylic acid grafted multi walled carbon nanotubes（PAA-g-MWCNTs）initiated by azodiisobutyronitrile（AIBN）.The analysis of the surface morphology,chemical composition,element content,structural defects and component content of PAA-g-MWCNTs,the results showed that AA successfully modified MWCNTs.Contact Angle measurement and dispersion test showed that the hydrophilicity of PAA-g-MWCNTs was significantly improved.PAA-g-MWCNTs showed an efficient adsorption performance for methylene blue（MB）.The adsorption effect was positively proportional to the initial concentration,p H value,adsorption time and temperature of the dye,and the maximum adsorption capacity was 329.8 mg g^-1.The adsorption process accords with pseudo-second-order kinetics model and Langmuir isotherm adsorption model.Further analysis shows that hydrogen bonding and electrostatic attraction are the key factors affecting the adsorption properties of PAA-g-MWCNTs.In addition,the relationship between the content of oxygen-containing groups and adsorption capacity of PAA-g-MWCNTs was fitted by mathematical model.In this study,PAA-g-MWCNTs with different dosages were blended with PVDF and the composite membrane was obtained by phase transformation.SEM analysis showed that the addition of PAA-g-MWCNTs was beneficial to the formation of finger-like pores in the composite membrane.The hydrophilic and mechanical properties of the composite membrane were significantly improved,the contact angle was reduced from 85.3°to 62.8°,the highest pure water flux was up to 288.5 L m^-2 h^-1,and the rejection rate of BSA by the composite membrane was still above 90%.The MB adsorption experiments showed that the adsorption capacity of the composite membrane increased with the increase of p H,adsorption time,initial dye concentration and temperature,and the maximum adsorption capacity was 8.7 mg g^-1.The adsorption process conforms to the pseudo-second-order kinetic model and the Freundlich isothermal adsorption model.This indicates that the composite membrane has adsorption saturation state for MB and multilayer adsorption occurs,and it is inferred that the adsorption process is affected by electrostatic interaction,hydrogen bonding,π-πelectron coupling,surface and pore structure of the composite membrane.In addition,thermodynamic analysis shows that the adsorption of MB by composite membrane is a spontaneous endothermic physical process.