nc

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known because of its useful electronic, photonic, and electrolu-

cyclodextrins and polyacids were also used as a soft-template toprepare nanofibers and nanotubes of conducting polymers [8

because of its stiffness of the PANI backbone and the hydrogen-

electrochemical polymerization. In this polymerization method,the obtained PoPDusually has an irregularmorphology. Recently,Sun et al. prepared 1D nanostructures of PoPD by directly mixingHAuCl and oPD aqueous solutions at room temperature without

Materials Letters 61 (2007)14]. Recently, interfacial polymerization, dilute polymerizationminescence properties, as well as potential applications in elec-trode materials, microelectronics, electrochromic materials andantisepsis [13]. In recent years, one-dimensional nanostructuresincluding nanofibers, nanotubes, nanorods and nanobelts ofconducting polymers have been studied extensively. These 1Dnanostructured materials have distinctive geometries, and novelphysical and chemical properties, which are probably applicablein nanodevices [4]. There are many methods to be developed forsynthesizing 1D conducting polymers. For example, a hard-tem-plate based method to prepare 1D conducting polymers was firstinvestigated [57]. Micelles, surfactants, liquid crystals, thiolated

bonding interactions between the amine moieties of adjacentchains. Therefore, polymers based on aniline derivatives havealso been extensively investigated.

Poly(o-phenylenediamine), PoPD, is a polyaniline derivativewhich can be achieved through substituting hydrogens by anamino group in an aniline nucleus. Compared with PANI, theoxidative polymer of oPD has apparently shown different charac-teristics of molecular structure and properties. It has been used asan electrochemical reduction catalyst for dioxygen, anticorrosioncoatings for metals, sensors for some chemical species and im-munosorbent assays [1821]. PoPD is usually prepared bywas higher than 0.12 M, the length of the microrods became very short and the diameter became bigger. Fourier transform infrared spectroscopy(FTIR), UVvis absorption spectra and X-ray diffraction (XRD) were used to characterize the structure of the obtained PoPD microrods. 2006 Elsevier B.V. All rights reserved.

Keywords: Poly(o-phenylenediamine); Microrods; Ferric chloride

1. Introduction

In the past decades, conducting polymers have become well-

and fiber seeding methods were developed to prepare PANInanofibers [1517]. However, the major disadvantage of PANI isits insolubility in common organic solvents and its infusibilitymorphologies of the resulting PoPD were confirmed by scanning electron microscopic (SEM) and transmission electron microscopic (TEM)images. When the concentration of o-phenylenediamine (oPD) was 0.03 M, the microrods of PoPD had a diameter in the range of 0.52 m and alength from 2 m to 20 m. It was found that the concentration of oPD monomer had much influence on the morphology of the obtained PoPD.When the concentration of oPD was lower than 0.03 M, long microrods could be observed. However, when the concentration of oPD monomerPreparation and characterizatiomicrorods using ferric

Xiaofeng Lu a, Hui Mao a, Danming Chao a,a Alan G. MacDiarmid Institute, Jilin U

b Department of Chemistry, Drexel U

Received 4 April 200Available onlin

Abstract

Microrods of poly(o-phenylenediamine) (PoPD) were synthesized b Corresponding author. Tel./fax: +86 431 5168924.E-mail address: wjzhang@jlu.edu.cn (W. Zhang).

0167-577X/$ - see front matter 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.matlet.2006.07.040of poly(o-phenylenediamine)hloride as an oxidant

aogang Zhao a, Wanjin Zhang a,, Yen Wei b

rsity, Changchun 130012, P. R. Chinaersity, Philadelphia, PA 19104, USA

ccepted 13 July 2006August 2006

templateless method using ferric chloride as an oxidant. The microrod

14001403www.elsevier.com/locate/matlet4

using any template or surfactant [22]. However, the resultingprecipitates are not pure, and there are someAu nanoparticles inthe final product.

TEM image of the as-synthesized PoPDmicrorods is shown in Fig. 1c. Itis found that the PoPD microrods seem to be composed of many thinfibers. The influence of the concentration of oPD on the morphologies ofPoPD is studied. SEM images of PoPD microrods synthesized withdifferent concentrations of oPD are shown in Fig. 2. It is found that whenthe concentration of oPD is lower than 0.03 M, the morphology isdominated by the microrods with a high ratio of length to diameter.However, when the concentration is higher than 0.12 M, the length ofPoPD microrods is reduced below 5 m, while the diameters of most

1401etters 61 (2007) 14001403In this article, we describe the preparation of PoPD microrodswith different lengths using ferric chloride as an oxidant. In thismethod, ferric chloride is reduced to FeCl2 which can be easilyremoved by washing with water. Therefore, the obtained PoPD ispure. Moreover, TEM image shows that the resulting 1Dstructures with high ratio of length to diameter are not solid andare composed of many thin fibers.

2. Experimental

2.1. Materials

All the reagents including oPD, ferric chloride and ammoniumperoxydisulfate were of analytical grade (AR), and used withoutfurther purification.

2.2. Preparation of PoPD microrods using ferric chloride asan oxidant

PoPDmicrorodswere synthesized by chemical oxidation usingferric chloride as an oxidant. In a typical procedure, differentcontent of oPD monomer was dissolved in 30 mL de-ionizedwater at room temperature. Then 10mL aqueous solution of ferricchloride (themolar ratio of ferric chloride to oPD is 1:1)was addedto the above mixture under vigorous stirring at room temperaturefor 5 h. The resulting precipitate was washed with water twice.Finally, the product was dried in vacuum at 50 C for 24 h.

2.3. Characterization

Scanning electron microscopy (SEM) measurements wereperformed on a SHIMADZU SSX-550 microscope. Transmis-sion electron microscopy (TEM) experiments were performedon a Hitachi H-8100 electron microscope with an accelerationvoltage of 200 kV. Gel permeation chromatography (GPC)instrument was equipped with a Shimadzu GPC-802D gelcolumn and SPD-M10AVP detector and with N,N-dimethyl-formamide as an eluent at a flow rate of 1 mL min1. FTIRSpectra of KBr powder-pressed pellets were recorded on aBRUKER VECTOR22 Spectrometer. UVvis absorptionspectra of PoPD microrods were recorded on a Shimadzu UV-2501 PC Spectrometer. X-ray diffraction patterns (XRD) wereobtained with a Siemens D5005 diffractometer using Cu Kradiation.

3. Results and discussion

In the conventional preparation of polyaniline and its derivative bychemical oxidation polymerization, ammonium peroxydisulfate andferric chloride were usually used as common oxidants. In this experiment,we polymerized oPD using the above two oxidants. Fig. 1a and b presentsSEM images of the PoPD samples synthesized under 0.03 M oPDmonomer using ferric chloride and ammonium peroxydisulfate as oxi-dants, respectively. It reveals that the sample synthesized using ferricchloride as an oxidant has rod-like morphology, while no one-dimen-

X. Lu et al. / Materials Lsional morphology of PoPD can be found by ammonium peroxydisulfateas an oxidant. The diameters of themicrorods are in the range of 0.5m to2 m and the length is about several to tens of micrometers. A typicalFig. 1. SEM images of PoPD microrods by chemical oxidation polymerization

using (a) ferric chloride and (b) ammonium peroxydisulfate as an oxidant underthe concentrations of oPD=0.03 M. (c) TEM image of PoPD microrods usingferric chloride as an oxidant under the concentrations of oPD=0.03 M.

ette1402 X. Lu et al. / Materials LPoPD microrods increased to more than 2 m. The formation of PoPDmicrorods is probably related to the self-assembly of PoPD throughintermolecular interactions and electrostatic repulsion interactions,which is similar to a previous report [23].

The molecular weight and polydispersity of the resulting PoPDdetermined by gel permeation chromatography (GPC) with uniformpolystyrene standards are ca. 2308 and 1.002, respectively. This resultdemonstrated that the obtained PoPD has about 22 units of oPDmonomer, which is a little higher than that synthesized by AgNO3 asoxidant [23]. Fig. 3a gives typical FTIR spectra of PoPD microrods.The bands at 3382 and 3306 cm1 are due to the characteristic NHstretching vibrations of the NH group. The broad peak at around3194 cm1 can be assigned to the NH stretching vibration of the NH2 group. The two bands at around 1525 and 1648 cm

1 are assignedto the stretching vibration of the C_C and C_N in the phenazine ring,respectively. The presence of the bands appearing at 758 and 586 cm1

is characteristic of the CH out-of-plane bending vibrations of benzenenuclei in the phenazine skeleton. The peaks at 1237 and 1363 cm1 areassociated with the CN stretching in the benzenoid and quinoid imineunits, respectively. All of these data are similar to a previous report,which confirm that the obtained microrod sample is PoPD [24].

Fig. 3b presents the UVvisible spectra of the PoPD microrodsdispersed in water solution. The major peaks at about 258 and 437 nmare observed. The band near 437 nm is assigned to transitionassociated with the phenazine ring conjugated to the two lone pairs ofnitrogen of the NH2 groups. The other peak at about 258 nm is mainly

Fig. 2. SEM images of PoPDmicrorods using ferric chloride as an oxidant under differentand (d) [oPD]=0.48 M.rs 61 (2007) 14001403assigned to the transitions of the benzenoid and quinoidstructures. The X-ray diffraction pattern of the PoPD microrods isshown in Fig. 3c. From it we can find that a series of sharp linesbetween 5 and 40 are observed, which indicates that the obtainedsample has good crystallinity and long range ordering.

4. Conclusions

In summary, microrods of PoPD have been synthesizedusing ferric chloride as the oxidant. It is found that theconcentration of oPD has much influence on the morphologiesof PoPD. We think that the mechanism of microrods formationmay be related to the self-assembly of PoPD throughintermolecular interactions and electrostatic repulsioninteractions. FTIR, UVvis absorption spectra and XRD areused to characterize the structure of microrods of PoPD, whichindicate that the obtained microrod sample is indeed PoPD.

Acknowledgements

The financial support from the Major International Collab-orative Project of National Natural Science Foundation of China(Grant 20320120169), the National Major Project for Funda-mental Research of China (National 973 Program No.

concentrations of oPD. (a) [oPD]=0.0075M; (b) [oPD]=0.03M; (c) [oPD]=0.12M;

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Preparation and characterization of poly(o-phenylenediamine) microrods using ferric chloride a.....IntroductionExperimentalMaterialsPreparation of PoPD microrods using ferric chloride as an oxidantCharacterization

Results and discussionConclusionsAcknowledgementsReferences