ZIF-8_改性聚丙烯腈电纺纳米纤维的制备及其高效去除水中孔雀石绿.pdf

第39卷第10期2023年10月Vol.39 No.1019591968无机化学学报CHINESE JOURNAL OF INORGANIC CHEMISTRY收稿日期：20230330。收修改稿日期：20230628。江苏省自然科学基金(No.BK20130969)和江苏省林业科技创新与推广项目(No.LYKJNANJING202202)资助。通信联系人。Email：ZIF8/改性聚丙烯腈电纺纳米纤维的制备及其高效去除水中孔雀石绿徐鹏1戴伟1石伟山2邢刚2王钊贵3王莎莎1李群1游超群1郝德君,3(1南京林业大学化学工程学院，南京210037)(2江苏艾津作物科技集团有限公司，南京210000)(3南京林业大学林学院，南京210037)摘要：通过原位生长方法，将最常见的金属有机骨架(MOFs)沸石咪唑酯骨架材料(ZIF8)固定到羧甲基化聚丙烯腈静电纺丝纳米纤维(PANCOOH NFs)表面，得到ZIF8/PANCOOH NFs。通过扫描电子显微镜(SEM)、能量色散光谱(EDS)、X射线粉末衍射(XRD)和傅里叶变换红外光谱(FTIR)对合成的ZIF8/PANCOOH NFs形貌和结构进行表征，并深入研究ZIF8/PANCOOHNFs从废水中去除孔雀石绿(MG)的性能。研究发现：ZIF8/PANCOOH NFs对MG的吸附符合拟二级动力学方程，吸附过程可采用Langmuir等温线模型拟合，其对MG的最大吸附容量可达3 604 mgg-1。此外，ZIF8/PANCOOH NFs在染料吸附实验中表现出良好的分离功能和重复利用性。关键词：ZIF8；静电纺丝；纳米纤维；聚丙烯腈；吸附；孔雀石绿中图分类号：TB333文献标识码：A文章编号：10014861(2023)10195910DOI：10.11862/CJIC.2023.154Preparation of zeolitic imidazolate frameworks8/modified polyacrylonitrileelectrospun nanofibers for efficient removal of malachite green from waterXU Peng1DAI Wei1SHI WeiShan2XING Gang2WANG ZhaoGui3WANG ShaSha1LI Qun1YOU ChaoQun1HAO DeJun,3(1College of Chemical Engineering,Nanjing Forestry University,Nanjing 210037,China)(2Jiangsu Aijin Crop Science and Technology Group Co.,Ltd.,Nanjing 210000,China)(3College of Forestry,Nanjing Forestry University,Nanjing 210037,China)Abstract:A simple insitu growth method was presented to synthesize zeolitic imidazolate framework8(ZIF8),oneof the most common metalorganic frameworks(MOFs)crystals,onto a carboxymethylated polyacrylonitrile electrospun nanofibers(PANCOOH NFs).The synthesized ZIF8/PANCOOH NFs were characterized by fieldemissionscanning electron microscope(SEM),energy dispersive spectroscopy(EDS),Xray powder diffraction(XRD),andFouriertransform infrared(FTIR)spectroscopy.The characterization results confirmed that the ZIF8 particles weresuccessfully loaded on the surface of the PANCOOH NFs.The ability of ZIF8/PANCOOH NFs to remove malachite green(MG),a model organic dye,from wastewater was evaluated to examine the potential of this novel materialas an adsorbent.The adsorption to MG was consistent with the pseudosecondorder kinetic equation,and theadsorption process was expressed by the Langmuir isotherm model.The maximum adsorption capacity for MG wasexamined as 3 604 mgg-1.It is noteworthy that the ZIF8/PANCOOH NFs could be easily separated from the dyesolution and regenerated through a simple washing process for recycling.Keywords:ZIF8:electrospinning;nanofiber;polyacrylonitrile;adsorption;malachite green无机化学学报第39卷0IntroductionNowadays,as the industry is leaping forward,organic dyes have become one of several major waterpollutants,and the removal of the organic contaminantsbefore discharged into the environment takes on a critical significance14.Among several methods(e.g.,electrochemistry,photochemistry,biodegradation,andadsorption)58,adsorption is one of the most attractivemethods for its simplicity and efficiency910.Numeroustraditional adsorbents(e.g.,activated carbon,zeolites,clay,cellulosic materials,and graphene composites)have been extensively used to remove organic dyesfrom industrial wastewater over the past few years1113.However,some of the above adsorbents face some challenges(e.g.,low adsorption capacity,poor selectivity,low surface areas,and poor stability).Thus,to enhancethe adsorption performance,efficient and highcapacityadsorbents of dye wastewater treatment should beexplored in depth.Metal organic frameworks(MOFs)have widelyserved as adsorbents for plentiful pollutants from wastewater for their good micropore structure and sufficiently high physical stability1418.Typical water stableMOF(e.g.,UiO66,MIL125,ZIF7,and ZIF8)exhibits excellent dye adsorption properties1923.However,some defects such as powdered morphology and fragility restrict their practical applications.To overcome theabove defects,the integration of MOF powder into afunctional support substrate is a promising approach,which makes it easy to recycle and reuse in dye adsorption2427.The electrospun nanofibers have recently acted asoutstanding substrates for loading MOF crystals fortheir high surface area,high porosity,and large surfacearea to volume ratio2831.Moreover,the surface of electrospun nanofibers can be easily modified by functionalgroups,thus assisting the initial coordination of metalirons to the surface of the substrate and facilitating theuniform growth of MOF particles3234.Based on the above discussion,zeolitic imidazolate framework8(ZIF8)crystals were loaded onto thecarboxymethylated polyacrylonitrile electrospun nanofibers(PANCOOH NFs)using an insitu growth method.To examine the adsorption performance of ZIF8/PANCOOH NFs,malachite green(MG)was selected as themodel organic dye for the batch adsorption experiments.Furthermore,the kinetic and isothermal modelswere studied by the experimental data,and the reusability of the ZIF8/PANCOOH NFs was evaluatedthrough the cycling test.1Experimental1.1MaterialPolyacrylonitrile(PAN,Mw=150 000)and N,N dimethylformamide(DMF)were offered by SigmaAldrich Co.,Ltd.(Shanghai,China).2Methylimidazole(2 MIM)was purchased from Shanghai Macklin Co.,Ltd.(Shanghai,China).Zincnitratehexahydrate(Zn(NO3)26H2O)was provided by Nanjing ChemicalReagent Co.,Ltd.(Nanjing,China).Malachite green(MG)was supplied by Sinopharm Chemical ReagentCo.,Ltd.(Shanghai,China).1.2Synthesis of PANCOOH NFs1.5 g of PAN was dissolved in 13.5 g of DMF toprepare the electrospinning solution.Subsequently,theelectrospinning solution was added to a syringe with a21G needle at an applied voltage of 20 kV.The distance between the needle tip and the collector was 15cm.After electrospinning,the obtained nanofiberswere dried in a vacuum oven at 60 for 12 h.Theobtained PAN NFs were hydrolyzed in a 1.0 molL-1NaOH solution at 50 for 1 h to convert surfacenitrile groups into carboxylic groups,and marked asPANCOOH NFs.The obtained PANCOOH NFs weredried in a vacuum oven at 55 for 12 h.1.3Preparation of ZIF8/PANCOOH NFs andZIF8/PAN NFs0.02 g of PANCOOH NFs was mixed with 0.587g Zn(NO3)26H2O in 40 mL methanol for 24 h.Subsequently,2MIM methanol solution(1.298 g,40 mL-1)was slowly added,and the mixture was oscillated at ambient temperature for 24 h.The samples obtained werewashed with methanol for several times and then driedat 50 for 6 h.Afterward,the above procedure wasrepeated twice,and the nanofibers were termed ZIF8/PANCOOH NFs.ZIF8/PAN NFs were prepared using1960第10期the same method,by substituting PAN NFs for PANCOOH NFs.1.4Batch adsorption experimentThe batch adsorption experiments were performedwith 20 mL of MG solution by mixing 5 mg of PANCOOH NFs and ZIF8/PANCOOH NFs,respectively.The pH of the original MG solution was adjusted with0.1 molL-1NaOH solution and 0.1 molL-1HCl solution.The batch adsorption experiments were performedto investigate the factors for the initial pH of MG solution(26),contact time(10420 min),and initial MGconcentration(501 500 mgL-1)in terms of the adsorption of MG onto the ZIF8/PANCOOH NFs.All thebatch adsorption experiments were performed at 298K.The residual concentration of MG in the solutionswas confirmed with a UV Vis spectrophotometer atmax=616 nm.The adsorption capacity at equilibrium(qe,mgg-1),the adsorption capacity at each time(qt,mgg-1),and the removal efficiency(R)of the MG weredetermined using the formula below35:qe=()0-eVm(1)qt=()0-tVm(2)R=0-e0 100%(3)where 0,e,and t(mgL-1)represent initial concentration,concentration at t time,and equilibrium concentration of MG,respectively.Moreover,V(L)indicatesthe volume of the MG solution,and m(g)denotes themass of the adsorbent.1.5Desorption and regeneration experimentA certain quality of adsorbed ZIF8/PANCOOHNFs was immersed in a proportional amount of ethanolsolution.Subsequently,the solution was placed in ashaker at 25 for 12 h.The adsorbed dye(MG)wasreleased into the ethanol solution.Afterward,the nanofibers were adequately washed with deionized waterand then dried in the vacuum oven at 60 .Theadsorptiondesorption recycling experiment was repeated nine times.1.6CharacterizationThe chemical structure of the samples was confirmed using Fourier transform infrared spectra(FTIR,Nicolet,PerkinElmer,USA).The crystal structure ofthe obtained materials was characterized by Xray diffractometer(XRD,Rigaku,Japan)equipped with CuK radiation(=0.154 056 nm,45 kV,40 mA),andthe scanning of XRD was running from 5 to 60 at thespeed of 5()min-1.The surface morphologies and microstructure of the samples were observed under fieldemission scanning electron microscopy(SEM,Hitachi,Japan)with an acceleration voltage of 30 kV,and theelemental compositions of the composite nanofiberswere examined using energy dispersive spectroscopy(EDS)apparatus based on the FESEM.The specificsurface area was measured using an N2sorption instrument(Quantachrome AutosorbiQASIQ).Furthermore,the specific surface area was measured based on theBrunauerEmmettTeller(BET)method.2Result and discussion2.1Microstructure of ZIF8/PANCOOH NFsThe morphology and structure of the fabricatednanofibers were examined using SEM.As depicted inFig.1a and 1d,PAN NFs were intact,smooth,and uniform with an average diameter of about 200 nm.Afteralkaline hydrolysis,the surface roughness of PAN COOH NFs slightly increased(Fig.1b and 1e).Fig.1cand 1f illustrate the morphology of ZIF8/PANCOOHNFs.As depicted in these figures,the ZIF8 particleswith rhombic dodecahedral shapes successfully grewon the surface of PANCOOH NFs.The EDS mappingwas further examined(Fig.2a2c),thus indicating thatZIF8/PANCOOH NFs had a high content of Zn elements(mass fraction of 9.1%)and distributed evenlyon the surfaces of the nanofibers.The above resultsconfirmed that the ZIF 8 particles were successfullyloaded onto the nanofiber surfaces.N2adsorptiondesorption measurements were performed to characterize the pore structures of the samples.Fig.3a illustrates N2adsorption desorption isotherms of PAN NFs and ZIF8/PANCOOH NFs.Thespecific surfaces of them were calculated using theBET method.The specific surface area of PAN NFswas measured as 42 m2g-1,while the specific surface徐鹏等：ZIF8/改性聚丙烯腈电纺纳米纤维的制备及其高效去除水中孔雀石绿1961无机化学学报第39卷area of the nanofibers coated with the ZIF8 particleswas obtained as 256 m2g-1(Fig.3b).The significantlyincreased specific area of ZIF 8/PAN COOH NFswould create more active sites for adsorption.2.2Material properties analysisThe crystalline phases of the synthesized nanofibers were examined through XRD(Fig.4).PAN NFsand PAN COOH NFs indicated a strong diffractionFig.1SEM images of the nanofibers:PAN NFs(a,d);PANCOOH NFs(b,e);ZIF8/PAN NFs(c,f)Inset in c:corresponding element content.Fig.2SEM image(a),zinc mapping image(b),and EDS element analysis diagram(c)of ZIF-8/PAN-COOH NFs1962第10期peak at 16.9,corresponding to PAN crystals.TheXRD patterns of ZIF8 and ZIF8/PANCOOH NFsshowed intense diffraction peaks at 7.12,10.22,12.56,14,54,15.18,16.28,and 17.86,respectively,corresponding to the(011),(002),(112),(022),(013),and(222)planes of the ZIF8,which revealedthe growth of ZIF8 particles in the ZIF8/PANCOOHNFs.The interaction between ZIF8 particles and PANCOOH NFs was characterized through the FTIR analysis.As depicted in Fig.5,the comparison of the spectrum of original PAN NFs revealed that PANCOOHNFs exhibited two different absorption peaks at 1 650and 3 420 cm-1,corresponding to the stretching vibration of C=O and OH in carboxyl functional groups.The peaks at 954,1 175,and 1 309 cm-1belong to thestretching vibration of the imidazole ring.The typicalpeaks at 693 and 759 cm-1belong to the ZnN andZnO stretching vibration,respectively.The band at1 453 cm-1belong to CH2rocking and bending vibrations.The adsorption band at 2 243 cm-1belong tothe CN vibration.As revealed by the emergence ofthe new characteristic bands of imidazole ring and ZIF8 in the spectra of the ZIF 8/PANCOOH NFs,theabove substances existed in the sample.2.3Adsorption evaluation for ZIF8/PANCOOHNFsThe cationic dye(MG)was employed as theadsorption object to optimize the adsorption capacity ofZIF8/PANCOOH NFs.Batch adsorption experimentswere conducted to assess the adsorption behavior.2.3.1Effect of pHThe pH of the solution is an essential parameterinfluencing the adsorption process of dye molecules.Since the color of the MG solution changed under thealkaline condition,the pH values tested in the experiment varied in the range of 26.As depicted in Fig.6,Fig.3N2adsorption isotherms(a)and pore size distributions(b)of PAN NFs and ZIF8/PANCOOH NFsFig.4XRD patterns of PAN NFs,PANCOOH NFs,and ZIF8/PANCOOH NFsFig.5FTIR spectra for PAN NFs,PANCOOH NFs,and ZIF8/PANCOOH NFs徐鹏等：ZIF8/改性聚丙烯腈电纺纳米纤维的制备及其高效去除水中孔雀石绿1963无机化学学报第39卷the removal efficiency of MG by ZIF 8/PANCOOHNFs increased with the increase of pH from 2 to 4 andleveled off in the scope of 56.Under high acidic conditions,ZIF8 on the surface of ZIF8/PANCOOH NFswas dissolved,thus resulting in low removal efficiency.With the increase in pH,the surface charge of ZIF8/PANCOOH NFs became more negative,and the electrostatic interaction between MG and the nanofibersalso became stronger36.As revealed by the aboveresults,the optimal pH value of ZIF 8/PAN COOHNFs for MG adsorption was examined as 5.2.3.2Adsorption kineticsThe adsorption kinetics was studied to gain moreinsights into the adsorption mechanism and adsorptionrate of PANCOOH NFs and ZIF8/PANCOOH NFsfor MG.Fig.7a and 7d illustrate the effect of contacttime on the MG adsorption by PANCOOH NFs andZIF8/PANCOOH NFs,respectively.The adsorptioncapacity increased with the increase in the contacttime.As revealed by the results,the adsorption capacity of PANCOOH NFs reached equilibrium after 400min,while that of ZIF 8/PAN COOH NFs reachedequilibrium after 300 min.To analyze the adsorption kinetics indepth,thekinetic data were fitted by the pseudofirstorder andpseudosecondorder equations.The equations of thetwo dynamical models are generally expressed as3738:ln(qe-qt)=ln qe-k1t(4)t/qt=1/(k2qe2)+t/qe(5)where qt(mgg-1)denotes the adsorption capacity ofMG at any contact time t(min);qe(mgg-1)representsthe adsorption capacity of MG adsorbed at the equilibrium time;k1(min-1)and k2(gmg-1min-1)express theequilibrium rate constant of the pseudofirstorder andConditions:100 mgL-1MG,0.25 gL-1ZIF8/PANCOOH NFs,25,12 h.Fig.6Effect of pH on the adsorption of MG ontoZIF8/PANCOOH NFsConditions:pH=5,100 mgL-1MG,0.25 gL-1ZIF8/PANCOOH NFs,25,12 h.Fig.7Adsorption kinetic curves of MG on PANCOOH NFs and ZIF8/PANCOOH NFs(a,d),and correspondingpseudofirstorder kinetic model(b,e)and pseudosecondorder kinetic model(c,f)1964第10期pseudosecondorder kinetic,respectively.Table 1 liststhe adsorption kinetics parameters of MG dye molecules using PANCOOH NFs and ZIF8/PANCOOHNFs,and Fig.7b,7c,7e,and 7f present the corresponding graphs.The result suggested that the coefficients of correlation(R2)were found to be higher for the pseudosecondorder kinetics than those of the pseudofirstorderkinetic model,establishing that the adsorption to MGconformed to the pseudosecondorder kinetic equation.The above results confirmed t