Growing nano-petals on electrospun micro/nano fibers

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  • RSC Advances

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    View Article OnlineView Journal | View IssueResearch Branch of Functional Polymer Co

    Solid State Electronic, University of Electr

    Chengdu 610054, P. R. China. E-mail: liuxb

    Electronic supplementary informationSEM images of (a) HBFePc powder and Helectrospun PEN/HBFePc micro/nano beffect of SDS and CTAB, respectivelydeionized water. See DOI: 10.1039/c3ra47

    Cite this: RSC Adv., 2014, 4, 8699

    Received 13th December 2013Accepted 10th January 2014

    DOI: 10.1039/c3ra47596d

    www.rsc.org/advances

    This journal is The Royal Society of CGrowing nano-petals on electrospun micro/nanofibers

    Fanbin Meng and Xiaobo Liu*Novel architectures: growing petals on micro/nano fibers were

    fabricated via combining electrospinning with solvent-induced self-

    assembly. The size and morphology of nanoflowers grown on fibers

    can be well controlled by solvent, hyperbranched degree and

    surfactant. Furthermore, these nanoflowers-like micro/nano fibers

    treated in ethanol indicate stronger fluorescent properties.Self-assembly and self-organization based on the mutual non-covalent recognition of molecules is a very useful technique toobtain species with well-dened structure and properties.14 Inparticular, design of supramolecular structures through self-assembly can sufficiently satisfy various demands, such asvesicles,5 microcapsules,6 one-dimensional materials,7 andsome highly ordered organic nanomaterials.8 The constructionsof precisely dened molecular materials were designed toperform specic functions such as sensors,9 eld-effect tran-sistors,10 and photovoltaic.11

    Phthalocyanines (Pcs),12 as the typical representative offunctional supramolecular materials, are particularly attractivebuilding blocks through self-assembly because the intimatepacking of these aromatic macrocycles can result in rich pho-tophysical and photochemical properties. A well-designed nanoPC molecular assembly can produce desirable new functionsthat are not observed in the corresponding monomer due toexciton coupling. Great efforts have been developed to constructwell-dened nanostructured materials. For example, micro-tubular structure with photovoltaic properties was obtained bysimple solvent evaporation method depending on strong ppinteraction,13 Helical ribbons, hollow nanotubes and nanowiremposites, Institute of Microelectronic &

    onic Science and Technology of China,

    @uestc.edu.cn

    (ESI) available: Experimental Section;BFePc powder treated in ethanol, (b)ers, (c) PEN/HBFePc bers under the, (d) PEN/HBFePc bers treated in596d

    hemistry 2014bundles were produced depending on the cooperation ofintermolecular hydrogen bonding or metalligand coordinationbonding with pp interactions between tetrapyrrole rings.14

    However, self-assembled 3D hierarchical supramolecularnanostructure with controlled morphologies are little reported.It is a big challenge to develop simple and reliable fabricationmethods for hierarchically architectures with controlledmorphologies, which strongly affect the properties of nano-structured phthalocyanine. Therefore, it is necessary to developfabrication methods in which the structures can be indepen-dently and precisely controlled in different length scales.

    Herein, for the rst time we propose a simple and effectivemethod to fabricate multi-dimensional nanoowers-likehyperbranched phthalocyanine iron/polyarylene ether nitriles(HBFePc/PEN) bers by combining electrospinning with self-assembly of HBFePc. We made electrospinning technique as aplatform for fabricating hybrid nanobers, then postspinningtreatment of nanobers was combined to tune the structure andmorphology of nanobers, enabling the fabrication of complexarchitectures. Through combining electrospinning with self-assembly of HBFePc, novel multi-dimensional architectures:growing nanoowers and nanothorns on micro/nano bersurface can be obtained. Furthermore, these nanoowers-likemicrobers indicate strong uorescent properties.

    During the electrospinning of small-molecule HBFePcblending with the high-molecule PEN, the low molecular weightHBFePc with lower viscosity and higher mobility of moleculescould migrate to the ber surface to form core-sheath structure,due to the phase separation.15 Many distinct HBFePc bead oragglomerates wrapping on the nanober surface could beobserved from Fig. S5. Aer the subsequent solvent treatmentin ethanol, the morphology of composite bers can be changedfrom core-sheath structure to owers-like like structure.HBFePc nanopetals can grow on PEN ber surface (as shown inFig. 1).

    In order to elucidate the nanopetals growth, a series of time-dependent growth experiments were conducted. Growthprocess of PEN/HBFePc composite bers for different treatmentRSC Adv., 2014, 4, 86998702 | 8699

    http://dx.doi.org/10.1039/c3ra47596dhttp://pubs.rsc.org/en/journals/journal/RAhttp://pubs.rsc.org/en/journals/journal/RA?issueid=RA004017

  • Fig. 1 Flowers-like PEN/HBFePc micro/nano fibers.

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    View Article Onlineduration of 2, 4, and 10 h are displayed in Fig. 2ac, respectively.It can be seen that the length and thickness of the HBFePcnanopetals can be easily controlled by the treatment time.When the electrospun ber was kept in ethanol for 2 h, sparseHBFePc nanopetals were formed, wrapping the PEN ber axis asshown in Fig. 2a. When the reaction time reaches 4 h, nano-petals continue growing perpendicular to the ber. Meanwhilelarger scales nanopetals with longer size can be observed (200400 nm). Prolonging the duration to 10 h, thicker layers ofFig. 2 SEM of PEN/HBFePc fibers after different post-treatment timein ethanol for (a) 2, (b) 4 and (c) 10 h, respectively and PEN/HBFePcmicro/nano fibers with different hyperbranched degree of HBFePc: (d)treated for 2 h, (e) treated for 4 h, (f) treated for 6 h, respectively.

    8700 | RSC Adv., 2014, 4, 86998702nanopetals appeared surrounding the PEN bers as shown inFig. 2c, and the size of the more uniform HBFePc nanopetalsincreased than those treated for 2 h and 4 h, respectively. Thelengths of the petals can reach 1 mm (Fig. 2c). Thus, the HBFePcnanopetals can serve as seeds for guiding the nanopetalssubsequent growth to form owers-like structure. Fig. 2e and fshows the owers-like bers treated in ethanol for 12 h withdifferent hyperbranched degree of HBFePc. With the hyper-branched degree of HBFePc increased, the thickness of nano-petals decreases from 1937 to 1023 nm, but the density as wellas the length further increased. Longer reaction time appearedto be favorable to the formation of thinner, lager and moreuniform nanopetals.

    So why the composite bers show owers-like structuretreated in ethanol? Firstly, the structure of HBFePc powdertreated in ethanol was discussed. Fig. S4b shows the struc-ture of the HBFePc treated in ethanol for 10 h. Only part nano-petals structure can be observed. Futhermore, the thickness ofthe nanopetals is up tp 150 nm, much thicker than that in thePEN/HBFePc bers. The powder can't wholly disperse inethanol and can't contact with ethanol molecule fully. Thusthe HBFePc isn't easy to self-assemble into owers-likestructure. However, when HBFePC was electrospun into bers,it can wrap the 1-D PEN nanober and it can show highspecic surface areas due to the PEN nanobers as thesupport. So It can contact and react with ethanol molecularfully. Then self-assembly into owers-like structure is easy tobe got.

    UV-vis optical spectroscopy has proven to be a powerful toolto study the evolution of the molecule absorption spectra uponaggregation and the formation of ordered states.16 Fig. 3demonstrates the UV-vis absorption spectrum of PEN/HBFePcbers. From Fig. 3b, the strong Q-band absorption peak ofpure HBFePc powders occurs at 690 nm and a relatively weakpeak, seen as a shoulder, appears at 610 nm which should beFig. 3 UV-vis absorbance spectra of various samples. (a) pure PENfibers, (b) pure HBFePc powders and PEN/HBFePc composite fiberstreated in ethanol for 2 h (c), 4 h (d) and 10 h (e), respectively.

    This journal is The Royal Society of Chemistry 2014

    http://dx.doi.org/10.1039/c3ra47596d

  • Fig. 4 WCA and corresponding shapes of water droplets for the PEN/HBFePc fiber mats with respect to post-treatment time in ethanol.

    Communication RSC Advances

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    View Article Onlineassigned to metal-to-ligand charge transfer, due to the hyper-branched oligomeric phthalocyanine species.17 The absorp-tion at 350 nm is assigned to B band (pp* transitions of themacrocycle). Precedent to B-band peak, a third absorptionband at 256 nm is assigned to C band may be assigned to thebenzene rings absorption.13 The absorption peak at about300 nm is mainly attributed to the absorption peak of PENbackbone. However, compared with the HBFePc spectrum of(b), the B-band of PEN/HBFePc bers appears at 360 nm whichis red shied slightly as shown in Fig. 3c (blue arrow). Withincreasing the post-treatment time in ethanol, the absorptionpeak broadens. In the metalphthalocyanines, the Soret-bandis related to the front orbitals of the central metals in themetalphthalocyanines,13 thus this means that thesurrounding conditions of the central Fe ions are obviouslychanged in the bers. That is, there are a few FeO coordina-tion bonds between Fe ions in one molecule and an oxygenatom in another molecule, indicating the intermolecularaggregation were formed. This type of aggregation (J-typeaggregate) induced by metaloxygen coordination was alsoreported tetra(a-phenoxy) in zinc phthalocyanine molecules.18

    Besides, adding ethanol can inhibited the cofacial ppstacking of the Pc rings (H-type aggregate). Futhermore, linebroadening was also observed for C-band which exhibited linebroadening and slight red shied compared with that ofHBFePc as shown in Fig. 3 (red arrow). This was attributed to atight packing between the benzene rings of the substituted4,40-bis (3, 4-dicyanophenoxy) biphenyl moieties of HBFePc.13

    This indicates that there exist both the strong J-type aggregatebetween the phthalocyanine rings and the strong pp inter-action between the benzene rings of the substituted 4,40-bis (3,4-dicyanophenoxy) biphenyl moieties of HBFePc, and boththese interactions are responsible for the formation of owers-like structure.

    Thus based on the above discussion, a possible formationmechanism was proposed. The 4,40-bis (3, 4-dicyanophenoxy)biphenyl moieties of HBFePc act as hands for the formation ofnanosheet by tight packing between the benzene rings, whichdedicated the length of nanosheets, and the nanosheet servedas seeds can grow by J type nano aggregates induced by FeOcoordination interactions, which dedicated the thickness ofnanosheet. Then, driven by the minimization of the total energyof the system, the nanopetals aggregate and organize to formowers-like structure.

    On the literatures,1921 the surfactants are amphiphiliccompounds bearing hydrophilic group and hydrophobic tail,which can self-assemble into various micelles with increasingsurfactant concentration, such as spherical micelle and rodlikemicelle. Thus we also investigated the morphology control ofthe composite bers under the effect of anionic surfactantsodium dodecyl sulfate (SDS) and cationic surfactant n-hexa-decyltrimethylammonium bromide (CTAB), respectively (moredetails are shown in Fig. S6). With increasing concentration ofSDS, the surface morphology of composite bers treated inethanol/SDS gradually changed from nanopetals to nanothorns(Fig. S6b). However, only rough surface without nanopetalswas observed as shown in Fig. S6d.This journal is The Royal Society of Chemistry 2014Fig. 4 show the relationship between the water CA and thepost-treatment time of PEN/HBFePc bers. It can be seen thatowers-like bers display higher contact angles with more post-treatment time. The WCA can be tuned by the morphologychange. The brous mats treated for 10 h can exhibite ahydrophobic state with a contact angle of 145. With the post-treatment time in ethanol increasing, the scales of nanopetalsincreased, and more interspace can be got as shown in Fig. 2.The contribution of the presence of cooperative ternary struc-tures between the petal sheets and nanobers can made itpossible to trap a large amount of air and minimize the realcontact area between surfaces and water droplets.22,23 Thus highWCA can be got.

    The spectroscopic, photophysical and photochemicalbehavior of PC aggregates strongly depends upon the relativegeometry of the macrocycles, and has been discussed theoret-ically by Kasha.24 The optical properties of the aggregates areusually illustrated by Davydov's exciton coupling theory.25 Thechanges in these properties resulting from aggregation canhave a major impact on the applications of PCs as light-har-vesting antenna, molecular wires, non-linear optics andpotential photodynamic therapeutic (PDT) agents. H-type PCdimers or higher aggregates are known to be non-photoactive,because such stacking provides an efficient nonradiativeenergy relaxation pathway, reducing the triple-state populationand therefore inhibiting the generation of singlet oxygen,which is directly related to the death of tumor cells.18,26 H-typeaggregate can be formed in the composite bers treated indeionized water, which is non-photoactive.18 Thus FL of thedeionized water treated PEN/HBFePc is non-uorescent asshown in Fig. 5b. However, The FL intensity of nanopetals-likebers was signicantly enhanced, exhibiting the emissionmaximum occurring at 455 nm, when exited at 344 nm. This isdue to the J-type aggregate of HBFePc.18 Futhermore, itsintensity was stronger than that of HBFePc treated in ethanol.This may be attributed to the 3-D unique architectures. Itindicated adding ethanol can not only inhibit the cofacial ppstacking (H-type aggregate) of the Pc rings, but also enhancethe uorescence property. Additionally, the visibleRSC Adv., 2014, 4, 86998702 | 8701

    http://dx.doi.org/10.1039/c3ra47596d

  • Fig. 5 Fluorescence spectra of PEN/HBFePc-4h fibers (a) withouttreatment, (b) treated in deionized water and (c)HBFePc treated inethanol and (d) PEN/HBFePc-4h fibers treated in ethanol. Emissionspectra (lex 344 nm).

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    View Article Onlinephotocatalytic properties of the owers-like PEN/HBFePc bersare undergoing.

    Conclusions

    We have prepared novel owers-like PEN/HBFePc bers that aregenerated from the combination of electrospinning with selfassembly. The HBFePc nanopetals can grow on PEN bers bythe post-solvent treatment. The morphology and size of nano-petals and nanothorns can be easy controlled. Furthermore,these nanoowers-like microbers in...

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