Functionalized Electrospun Polyacrylonitrile (PAN)anofibers: Synthesis, Characterization and Environmental Applications

Abstract

Electrospinning is a simple, convenient and low cost process that can produce ultrafine continuous polymer fibers having diameter in the nanometer range. The functionalization of electrospun (e-spun) nanofibers surface with suitable organic/inorganic reagents improves their properties, which will lead to a significant expansion of their applications especially in the field of adsorption, separation and membrane technology. In our present work, we have synthesized PAN polymer nanofibers by electrospinning method. We have studied here, the surface functionalization of PAN nanofibers by converting the –CN group into carboxylate (anionic) and amine (cationic) functional groups and also immobilization of inorganic nanoparticles onto the nanofibers surface. The functionalized e-spun nanofibers have been used for adsorptive removal of toxic organic pollutants from aqueous solution and also growth inhibition study of pathogenic microorganisms. The functionalized membranes were characterized by FTIR, FE-SEM, BET, XRD, TEM, EDAX, etc., analytical techniques and adsorption studies were investigated by using UV-Vis Spectrophotometer. The carboxylate functionalized PAN nanofibers membrane was used as adsorbent for removal of cationic dye, Malachite green (MG) from the aqueous solution. The experimental results showed that 99% MG dye was removed by functionalized nanofibers within 30 min of contact time. The equilibrium adsorption capacity was found to be 200 mg/g which is almost 5 times higher than that of un-functionalized PAN nanofibers.

We have also functionalized the nanofibers surface with amine functional groups for generation of a cationic surface charge to target anionic pollutant species from water. Three different chemical procedures have been adopted to synthesize three different amine functionalized nanoadsorbent materials i.e. PAN nanofibers matrix containing three different amine functional groups such as PAN-NH2, PAN-CONH2 and PAN-EDA. The ATR- FTIR analysis confirm the presence of amine (-NH2) and amide (-CONH2) functional groups on PAN nanofibrous membrane. The obtained three different amino functionalized PAN nanofibrous matrixes were used as adsorbent for removal of toxic anionic congo red (CR) dye from aqueous media. Among the three different nanoadsorbents, the ethylene diamine functionalized nanofibrous (PAN-EDA) matrix is found to be most efficient adsorbent material for decontamination of CR dye and can also be used as model affinity membrane for waste water treatment.

Apart from this, we have also synthesized iron oxide functionalized PAN nanofibers by three different methods and have compared their removal efficacy for adsorption of CR dye from aqueous media. FE-SEM images clearly show the formation of iron oxide nanoparticles that are uniformly decorated on PAN nanofibers surface. The average diameters of the nanoparticle are found to be in the range of 30 to 120 nm. The batch adsorption experiments were carried out to elucidate the adsorption mechanism. The iron oxide mounted PAN composite nanofibers observed to be excellent nanoadsorbent material for the removal of CR dye owing to their simple preparation, high sorption capacity and low cost.

Furthermore, we have also attempted to functionalize the PAN nanofibers surface with heterostructure ZnO-Ag nanosized particles by using three different chemical pathways and the obtained functionalized nanocomposite mats have been used for antibacterial applications. In the first method, Zn(OH)2 and AgNO3 salt precursors have been added to PAN/DMF (8 wt%) solution. Then the solution mixture was refluxed at 1000C for 2 h followed by electrospinning to form ZnO-Ag nanoparticles functionalized PAN nanofibers membrane denoted as PAN/ZnO-Ag (R). In the second method, Ag doped ZnO nanoparticles (ZnO-Ag) were prepared previously and blended with (8 wt%) PAN/DMF solution. Then the prepared composite solution was electrospun to form PAN/ZnO-Ag (B) composite nanofibers matrix. In the third method, PAN/DMF/Zn(ac)2/AgNO3 mixed solution was prepared and then electrospun to form PAN/Zn(ac)2/AgNO3 composite nanofibers membrane. Then PAN/ZnO-Ag (H) composite nanofibers matrix was prepared by hydrothermal treatment of PAN/Zn(ac)2/AgNO3 composite nanofibers at 1500C in (NH4)2CO3 solution. From the FE-SEM and TEM images it was clearly observed that 20-30 nm size spherical nanoparticles have been decorated uniformly on the surface of PAN nanofibers. XRD study confirmed the formation of ZnO-Ag mixed/hybrid nanoparticles on nanofibers surface. The ZnO-Ag heterostructure nanoparticles functionalized PAN nanofibers membranes were used for antibacterial study. It was observed from inhibition zone test that the PAN nanofibers membrane functionalized with ZnO-Ag heterostructure nanoparticles prepared by reflux method shows excellent antimicrobial properties for both gram negative E. coli and Gram positive Micrococcus Luteus microbes than the single component counterparts such as PAN-Ag or PAN-ZnO nanofibers mats.