Synthesis, characterization and corrosion protection properties of polyaniline/TiO2 nanocomposite

Lian zhong a, Yanhua Wangb and Yonghong Luc

Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education; College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China

azhonglian0705@163.com, bwyhazz@163.com, clazake@163.com

Keywords: anticorrosion, polyaniline, Nano-composite, Titanium dioxide, Coating

Abstract. In this study, conductive polyaniline (PANi)–titania (TiO2) nanocomposites with

core–shell structure were prepared and their anticorrosion properties were investigated.

PANi/nano-TiO2 composite were prepared by in situ polymerization of aniline monomer in the

presence of TiO2 nanoparticles. The morphology and structure of the polymer nanocomposite was

characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy

(FTIR), respectively. SEM and FTIR spectra measurements show that PANi and TiO2 nanoparticles

are not simply blended or mixed up, and a strong interaction exists at the interface of nano-TiO2 and

PANi. From the anticorrosion investigation in 3.5%NaCl, it is revealed that the protective

performance of epoxy paint containing PANi/nano-TiO2 composite is significantly improved than

PANi or a mixture of polyaniline and nano-TiO2. From the improved anticorrosion performance, it

also indicate that PANi and TiO2 nanoparticles are not simply blended or mixed up, the strong

interaction exists at the interface of PANi and nano-TiO2. It is the strong interaction that results in the

coordinated effect and more excellent anticorrosion performance.

Introduction

Because of the environmental protection issues, studies on trend of replacing of zinc chromate in

primers by organic corrosion inhibitors have attracted much attention [1–2]. Conducting polymer

coatings have been shown to offer corrosion protection of ferrous and non-ferrous metals and

considered to be a promising replacer [3–4]. Among the conducting polymers, PANi is one of the

most promising materials because PANi is not only low-cost, highly stable in air but also exhibits the

corrosion inhibition behavior [5].

It has been reported that the barrier properties can be enhanced if one uses appropriate fillers in the

coatings [6]. Further, it has been shown that nano-particulate fillers give much better barrier

properties even at low concentrations than conventional micron size additives [7]. As TiO2 is one of

the main pigments which is usually used in the organic coatings, it is thought worthwhile to use

nano-particulate TiO2 as an additive to improve the barrier properties of PANi coatings as well as self

healing effect giving large advantage in anticorrosion behaviour. Hence, the present studies were

carried out on the preparation of PANi/ nano-TiO2 hybrid coating formulations using epoxy as the

matrix and investigating their suitability for anticorrosive coatings.

Experimental

Material

Aniline (ANI) (AR, Aladdin-reagent, China) was purified by distillation, TiO2 (rutile)

nanoparticles with an average particle size of approximately 20nm (Aladdin-reagent, China) was

used without further purification. Other chemicals used were of AR grade.

Preparation of PANi and PANi–TiO2 composites

To prepare PANi and PANi–TiO2 composites, the following steps were followed. 0g, 0.3 g of

TiO2 nanoparticles were added into a mixture of 1 ml aniline and 90 ml 1N HCl in a set of reaction

vessels. The mixtures were stirred with magnetic stirrers in ice water baths for 1 h to get a uniform

Advanced Materials Research Vols. 399-401 (2012) pp 2083-2086Online available since 2011/Nov/22 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.399-401.2083

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suspension of TiO2. To these mixtures, 100ml pre-cooled 1N HCl solutions containing 2.5 g APS

were added drop wise. The resulting mixtures were allowed to react in ice bath for about 4 h. From

these reactions we get pure PANi and PANi/nano-TiO2 composites. The products were washed with

distilled water for several times and at last washed with ethanol. Then all samples were dried at 60

in an oven for 12 h.

Measurements

The observation of the composite morphology was performed using a Hitachi S-4800 scanning

electron microscope (SEM). Fourier-transform infrared spectra (FTIR) of the samples were carried

out on a Nicolet 6700 spectrometer for which samples were palletized with KBr powder.

Preparation of PANi, PANi+ nano- TiO2, PANi/ nano- TiO2 dispersion formulations for coating

The 10 wt% of PANi, a mixture of PANi and nano- TiO2, PANi/nano- TiO2 powder was crushed

and dispersed in the epoxy resin with a high-speed mechanical stirrer, respectively. These yielded

uniform dispersions with no settling. The A3 steel electrode, which was sealed with epoxy resin,

leaving only one surface exposed to the testing environment, were polished by C-100 emery paper,

washed with acetone and dried. The yielded paint were brushed on the A3 steel electrode and dried at

room temperature for 30 min followed by baking in air circulating oven at 50 for 4 h to give final

coating with thickness in the range of 40–50µm.

Testing of corrosion resistance properties

For the investigation of the anticorrosion properties of the yielded coatings, the impedance

measurement was performed using an EG&G PAR Model 2263 Potentiostat/Galvanostat. The

working electrode was a paint-coated steel electrode. A saturated calomel electrode (SCE) was used

as the reference. The auxiliary electrode was a platinum grid. Impedance of the samples was

measured in the frequency range of 10 mHz to 100 kHz during exposure in 3% NaCl solution.

Results and discussion

Morphology and structure of the PANi/nano- TiO2 composite

Fig. 1a and b reveal scanning electron microscope (SEM) images of the unmodified TiO2

nanoparticles and the polyaniline coated TiO2 nanoparticles. The TiO2 nanoparticles have an average

diameter of 20 nm according to manufacturer’s specifications which is found to be consistent with the

SEM image in Fig. 1a, whereas the polyaniline coated TiO2 nanoparticles shows diameter ranging

from 30 to 40 nm (Fig. 1b). There is an increase in the particle size due to the formation of PANi

around the particles.

Fig. 2 shows the FTIR spectra of doped PANi and PANi/nano- TiO2 composite (10% PANi

loading and doped with HCl), respectively.

The main characteristic peaks doped PANi (Fig. 2a) are assigned as follows: the band at 3443 cm-1

is attributable to N–H stretching mode, C=N and C=C stretching mode for the quinonoid and

benzenoid units occur at 1560 and 1488 cm-1

, the bands at 1296 and 1241 cm-1

is attributed to C–N

stretching mode for benzenoid unit, while the band at 1108 cm-1

is due to quinonoid unit doped PANI,

and the peak at 801 cm-1

is associated with C–C and C–H for benzenoid unit.

Fig. 2b indicates that the main characteristic peaks doped PANi appear in the composite, which are

3385, 1578, 1496, 1302, 1246, 1142 and 800cm-1

, respectively. Also, Fig. 2b reveals that the

maximum peak of TiO2 (510 cm-1

) occurs in the composite. However, all bands shift slightly. In

addition, a new peak (914 cm-1

) appears in PANi/nano- TiO2 composite. These results indicate that a

strong interaction exists at the interface of PANi and nano-TiO2. When (NH4)2S2O8 is added to the

reaction system, polymerization proceeds initially on the surface of TiO2 nanoparticles. It leads to

adhesion of the PANi to the TiO2 nanoparticles [8]. Because titanium is a transition metal and titanic

has intensely tendency to form coordination compound with nitrogen atom in PANi molecular, such

adhesion will not only constrain the motion of PANI chains, but also restrict the modes of vibration in

PANI molecular. The strong interaction causes the shifts of bands and the appearance of a newpeak.

Moreover, the action of hydrogen bonding between nano- TiO2 and PANi molecular is also

contributory to the shift of bands.

2084 New Materials, Applications and Processes

Fig.1. SEM images of (a) unmodified TiO2 nanoparticles and (b) PANi/nano-TiO2 nanoparticles.

4 0 0 0 3 5 0 0 3 0 0 0 2 5 0 0 2 0 0 0 1 5 0 0 1 0 0 0 5 0 0

1 2 4 1

a

3 3 8 5 8 0 0

1 5 7 8

1 4 9 6

1 2 4 6

1 3 0 2

1 5 6 01 4 8 8

1 2 9 6

1 1 4 2

1 1 0 8

8 0 1

9 1 4

3 4 4 3

b

w a v e n u m b e r ( c m- 1)

5 1 0

Fig. 2. FTIR spectra of (a) doped PANi, (b) PANi/nano-TiO2 composite.

Anticorrosion properties of PANi/ nano-TiO2 composite

Fig. 3 shows the impedance spectra of the painted samples after 80 days of immersion in solution

of 3% NaCl. We can see that the impedance spectra all include two loops, the first well-defined

capacitive loop in high frequency, and the second unclearly defined capacitive loop in low frequency

part. When compared impedance spectra with each other, it can be seen that the height of the first loop

gradually increased from 1 to 3 in high frequency part. The first loop in high frequency characterized

the films resistances and its height increase means the primer’s protective performance is improved.

Fig. 4 shows the variation of the low frequency impedance values for different immersion time of

painted samples in 3% NaCl solution. It can be seen that the low frequency impedance values all

decrease by the increasing immersion time, and the reduction state increase from 3 to 1. These results

are in accordance with the result of the impedance spectra. The low frequency impedance values

continue to remain high (108Ω ) for PANi/nano-TiO2 even after exposure to the corrosive

environment. This is clear indication of the excellent protection against corrosion. These results

indicate that the nano- TiO2 additive improve certainly the barrier properties of PANI coatings, and

the coatings’ anticorrosion performance have been further improved by PANi/nano-TiO2 composite

additive with core–shell structure. We believe that it is the strong interaction of PANi and nano-TiO2

exists in the PANi/nano-TiO2 composite additive that results in the synergistic effect and more

excellent anticorrosion performance.

(a) (b)

Advanced Materials Research Vols. 399-401 2085

0 1x108

2x108

3x108

4x108

0.0

5.0x107

1.0x108

1.5x108

0.0 4.0x105

8.0x105

1.2x106

1.6x106

0.0

2.0x105

4.0x105

6.0x105

0.0 5.0x106

1.0x107

1.5x107

2.0x107

2.5x107

0.0

2.0x106

4.0x106

6.0x106

Zim (ohms)

Zre (ohms)

PANI/nano-TiO2/epoxy 80days

PANI/epoxy 80days

PANI+nano-TiO2/epoxy 80days

0 20 40 60 80

106

107

108

109

1010

Time / d

Z

/

/

/

/ ΩΩ ΩΩ

PANI/epoxy

PANI+nano-TiO2/epoxy

PANI/nano-TiO2/epoxy

Conclusions

(1) Polyaniline/ nano-TiO2 composite has been prepared by chemical oxidation method in the

presence of aniline and nano-TiO2 by ammonium persulfate oxidant. SEM micrograph show that

the PANi/ nano-TiO2 composite has a core–shell structure. FTIR data have indicated that PAn and

TiO2 nanoparticles are simply not blended or mixed up. Appearance of new peaks demonstrates

that a strong interaction exists at the interface of PAn and nano-TiO2.

(2) The anticorrosion investigations show that the nano- TiO2 additive improve certainly the barrier

properties of PANI coatings, and the coatings’ anticorrosion performance have been further

improved by PANi/nano-TiO2 composite additive with core–shell structure. We believe that it is

the strong interaction of PANi and nano-TiO2 exists in the PANi/nano-TiO2 composite additive

that results in the synergistic effect and more excellent anticorrosion performance.

Acknowledgements

This work was financially supported by the Shandong Natural Science Foundation (ZR2010DQ006)

and Young teachers fund project of Ocean University of China (201013014).

References

[1] D.W. Deberry, J. Electrochem. Soc. 132 (1985) 1022.

[2] P.J. Kinlen, Y. Ding and D.C. Silverman, Corrosion 58 (2002) 490.

[3] B.Wessling, J. Posdorfer, Electrochem. Acta 44 (1999) 2139.

[4] Yawei Shao, Hui Huang, Tao Zhang, Guozhe Meng, Fuhui Wang. Corrosion Science 51 (2009)

2906

[5] T. Schauer, A. Joos, L. Dulog, C.D. Eisenbach. Progress in Organic Coatings 33 (1998) 20

[6] N.K. Lape, E.E. Nuxoll, E.L. Cussler, J. Membr. Sci. 236 (2004) 29.

[7] D.J. Chako, A.A. Leyva, Chem. Mater. 17 (2005) 13

[8] T. Ozawa, Thermochimica 203 (1992) 159.

Fig. 3. Impedance spectra of the painted sample

after 80 days of immersion into 3%NaCl solution.

Fig. 4. Low frequency impedance of the painted

sample after exposure to 3%NaCl solution.

2086 New Materials, Applications and Processes

New Materials, Applications and Processes 10.4028/www.scientific.net/AMR.399-401 Synthesis, Characterization and Corrosion Protection Properties of Polyaniline/TiO2 Nanocomposite 10.4028/www.scientific.net/AMR.399-401.2083

DOI References

[1] D.W. Deberry, J. Electrochem. Soc. 132 (1985) 1022.

http://dx.doi.org/10.1149/1.2114008 [2] P.J. Kinlen, Y. Ding and D.C. Silverman, Corrosion 58 (2002) 490.

http://dx.doi.org/10.5006/1.3277639 [3] B. Wessling, J. Posdorfer, Electrochem. Acta 44 (1999) 2139.

http://dx.doi.org/10.1016/S0013-4686(98)00322-3 [4] Yawei Shao, Hui Huang, Tao Zhang, Guozhe Meng, Fuhui Wang. Corrosion Science 51 (2009) 2906.

http://dx.doi.org/10.1016/j.corsci.2009.08.012 [5] T. Schauer, A. Joos, L. Dulog, C.D. Eisenbach. Progress in Organic Coatings 33 (1998) 20.

http://dx.doi.org/10.1016/S0300-9440(97)00123-9 [6] N.K. Lape, E.E. Nuxoll, E.L. Cussler, J. Membr. Sci. 236 (2004) 29.

http://dx.doi.org/10.1016/j.memsci.2003.12.026 [7] D.J. Chako, A.A. Leyva, Chem. Mater. 17 (2005) 13.

http://dx.doi.org/10.1021/cm0302680 [8] T. Ozawa, Thermochimica 203 (1992) 159. Fig. 3. Impedance spectra of the painted sample after 80 days

of immersion into 3%NaCl solution.

http://dx.doi.org/10.1016/0040-6031(92)85192-X