Study On Polyaniline-Bentonite And Its Adsorption Behavior Of Reactive Green 19

Nowadays,the domestic and international research about modification of montmorillonite(MMT)mainly focus on using small organic molecules as the modifier,and the predominant adsorption mechanism of organic contaminants in water on organically modified MMT are physical adsorption.Considering the layered structures of MMT and unique physicochemical properties of polymer molecules,it is expected that polymer modified MMT may show different physical and chemical properties compared with small molecules modified MMT.Based on the general ideas of material design,theoretical calculation,structure characterization and performance test,three types of polyaniline-montmorillonite(PANI-MMT)nanocomposites were prepared in this study by in situ polymerization of aniline within the interlayers of MMT using ferric trichloride,cyclohexanone peroxide or persulfate as initiator,respectively.The PANI-MMT nanocomposites were further studied systematacially as adsorbents for the removal of green 19(RG-19)dye from water.Moreover,given the strong interactions between benzoid and quinoid rings of the PANI chain and azo dyes,the structure–property relationships of PANI-MMT were studied,which may provide theoretical basis and experimental supporting for the further application of montmorillonite in wastewater treatment.Firstly,the chemical composition and microstructure of montmorillonite were investgated this study.Then,a set of equations describing the relationship between interlayer structure and interlayer binding energy of montmorillonite were proposed.According to the relationship between enthalpy change during aniline polymerization and interlayer binding energy of montmorillonite,three different kinds of adsorbents,including PANI-MMT nanocomposites initiated by ferric trichloride(FC-PANI-MMT),PANI-MMT nanocomposites initiated by cyclohexanone peroxide(CP-PANI-MMT)and PANI-MMT nanocomposites initiated by persulfate(AP-PANI-MMT),were prepared.The chemical composition,chemical structure,interlamellar structure,pore structure and morphology of the PANI-MMT nanocomposites were characterized by FTIR spectroscopy,XRD,DSC and nitrogen adsorption isotherms.In addition,the relationship between interlayer structure of PANI-MMT nanocomposites and interlayer binding energy of montmorillonite was established on the basis of experimental results,which explored the essential influencing factors affecting the exfoliation degree of MMT.Secondly,the adsorption equilibrium,adsorption kinetic and thermodynamics of RG-19 on PANI-MMT nanocomposites were studied.Results indicated that the primary mechanism for RG-19 adsorption on PANI-MMT was chemical monomolecular adsorption.The equilibrium adsorption capacity of PANI-MMT was influenced by the initial concentration of dye,temperature and pH.Lastly,the change rules of interlamellar structure,electron energy state,group interaction and relative content during the RG-19 adsorption on PANI-MMT were studied using FT-IR,TEM,XRD,XPS and N2 adsorption-desorption measurement.And the relationships among material structure,adsorption mechanism and pollutant structure were also revealed.Based on systematic analysis and in-depth studies,an efficient approach to preparing polymer/montmorillonite with controllable interlayer(basal)structure was presented in this thesis.Besides,a novel strategy for exploring exploring the relationships between structures and properties of absorbent materials were developed.Therefore,this study will facilitate the application of MMT in the field of wastewater treatment,and is of great value in both academic and industrial areas.Main contributions of this work are as follows:(1)FTIR spectra showed that the characteristic absorption bands at 698 cm-1-791 cm-1 of aniline monomers disappeared,and new absorption bands attributed to quinonediimine/phenylenediamine structural unit of polyaniline have been observed in the 1389 cm-1-1645 cm-1 region after free-radical polymerization of aniline.In addition,the XRD patterns of PANI-MMT showed the characteristic peaks of polyaniline at 2θ values of 21.04° and 24.8°.Results of DSC and TG indicated that the interlayer water PANI-MMT had an higher decomposition temperature than that of MMT.Based on the above results and TEM microstructure analysis,it can be speculated that PANI-MMT adsorbents were prepared via in situ polymerization of aniline monomers within the interlayers of MMT.(2)Macromolecular model of MMT was established by chosing monoclinic cell structure of MMT as the repeating unit.Then,an equation that associated with cohesive energy,solubility parameter,molar mass of MMT unit cell,molar volume of MMT unit cell,and binding energy among MMT macromolecules was proposed.The molar mass and molar volume of MMT unit cell was 716 g/mol and 292.2 cm3/mol,respectively.The binding energy among MMT macromolecules was about 159997 J/mol.(3)The producing heat during free-radical polymerization of aniline for FC-PANI-MMT,CP-PANI-MMT,and AP-PANI-MMT were 408-952 J·100g–1,804-1876 J·100g–1 and 1404-3276 J·100g–1,respectively.It was found that the producing heat during aniline polymerization in various initiator system had a positive correlation with changes of the interlayer spacings.Thus,the PANI-MMT with controllable interlayer structures could easily be obtained via chosing different initiator systems.(4)The interlayer structure,pore structure and surface wettability were found to be the main factors influencing absorption performance of PANI-MMT.Kinetic studies showed that the adsorption of FC-PANI-MMT,CP-PANI-MMT,and AP-PANI-MMT followed a pseudo-second-order rate model.The adsorption isotherm data were fitted well to Langmuir isotherm.Compare with sodium MMT,PANI-MMT showed a larger interlayer spacing,higher mesopore volumes and lower hydrophilicity,which could facilitate the adsorption of RG-19.However,there was no linear relationship between saturation adsorption capacity and interlayer spacing,specific surface area,or contact angle of MMT.It’s worth pointing out that there was a linear relationship between saturation adsorption capacity of PANI-MMT and percentage of mesopore specific surface area,which was different from the rules showed by MMT intercalated with small molecules.(5)The interaction mechanism between RG-19 and PANI-MMT adsorbents was investigated.It was found that the adsorption behavior(such as interlayer distribution,electrostatic adsorption and hydrogen bonding)of PANI-MMT could be attributed to the phenyl structure,oxygen atom with lone-pair electrons and protonation of polyaniline.As mentioned,the primary mechanism for RG-19 adsorption on PANI-MMT was chemical adsorption.Besides,PANI-MMT possessed better hydrophobicity than MMT and its solubility parameter was close to that of RG-19,which may also be conducive to physical absorption of RG-19 molecules on PANI-MMT.The physical adsorption mechanism was similar to that of RG-19 absorption on MMT modified with small organic molecules.(6)The changes in adsorption quantity of RG-19 over the interlayer spacing of MMT in FC-PANI-MMT,CP-PANI-MMT,and AP-PANI-MMT were also studied.It was found that the adsorption quantity of RG-19 on PANI-MMT increased with the increasement of interlayer spacing of MMT.The results indicated that the adsorption took place mainly in the interlayer of PANI-MMT.Thus,the in situ intercalation polymerization of aniline within the interlayers of MMT provides an alternative and effective strategy for designing novel adsorbents.Introduction of polyaniline polymer chain into the interlayer space of MMT resulted in the chemical adsorption of RG-19 adsorption on PANI-MMT and became the key factor determining adsorption rate.