Graphene-MnO2 nano-composite as sensor for structural health monitoring of

civil infra structures *

Abstract Materials and method

Results and discussion

Fabrication of sensors and characterization

Corrosion monitoring by embedded Sensor in concrete structures

Acknowledgement

The authors thank to ESC-0110 Project for financial support

*Corresponding author: corrosaras@gmail.com

Electrochemical sensors are involved in the corrosion and structural health monitoring (SHM) of

concrete structures. In this investigation, a novel attempt has been made to synthesis Graphene

modified MnO2 (GO-MnO2) nanoparticles by chemical method. Synthesized material was

characterized by following analytic techniques such as Fourier transform infrared spectroscopy (FTIR),

X-ray diffraction (XRD), Raman spectra and Scanning Electron Microscopy (SEM). The results are

clearly indicated that MnO2 nanorods are monodispersed on Graphene surface. Graphene modified

MnO2 nanocomposites sensors are fabricated and embedded in concrete structures for corrosion

monitoring of reinforced steel. The suitability of the assembled sensor was evaluated by

electrochemical tests such as potential stability, sensing ability, reversibility and impedance

spectroscopy. GO-MnO2 showed perfect stability for the exposure period upto 30 days. The sensor

was embedded in concrete and the studies are under progress.

Fig shows the XRD pattern of MnO2 and GO-MnO2 were obtained by simple

chemical method. These diffraction peaks of synthesized MnO2 and GO-MnO2

were similar to tetragonal crystal phase of MnO2 (JCPDS; 65-2821) and

moreover high intensity peaks of GO at around 2θ= 11.2 and 27,2 corresponds

to the (001) and (002).

Raman spectra of MnO2 and GO-MnO2 are shown in Figure.

From the relative intensities of the D and G band peaks at

1350 and 1590 cm− 1, it can be concluded that the size of the

sp2 domains increases during reduction of GO. Moreover, the

similar MnO2 peak at 621.41 cm− 1was observed both samples.

a)

b)

2 4 6 8 10 12 14keV

0

1

2

3

4

5

6

7

cps/eV

Mn Mn O

C

2 4 6 8 10 12 14keV

0

1

2

3

4

5

6

7

8 cps/eV

Mn Mn O

C

MnO2)

GO-MnO2)

The morphology of the as synthesized MnO2 and GO-

MnO2 nanostructure is shown in Fig. Fig a is an bright

field TEM image of the MnO2 nanorod. These image

show well dispersed nanorods the diameter of the

individuals nanorod are in the range of 10-20 nm their

length are 0.1 to 0.2µm. Moreover, higher magnification

of TEM image of the MnO2 nanorods , to observed two

lattice fringe with a d-spacing of 0.32nm and 0.71nm,

corresponds to 101 and 111 of MnO2 crystal plane which

is coincide with XRD data and SAED diffraction. In

comparing Fig. (a) and (b), it can be clearly seen that

GO-sheet have been decorated with nanorods MnO2

structure. More over, the edge of the graphene sheet

represented the TEM image. There is no significant

observed that morphology of the MnO2 nanorods. The

similar MnO2 lattice fringe was observed on the GO-

MnO2 nano composite. Morphological study revealed

that the MnO2 nanorod crystal growth on the graphene

sheet. a) TEM image of the MnO2 nanorod and (b) GO-MnO2 nanocomposite

b) a)

TEM observation

FTIR spectra

Raman spectra XRD SEM –EDAX observation

A structure of GO-MnO2 electrode.

Sensors assembled in concrete structures

Analytical characterization

FT-IR,

Raman spectra,

XRD pattern,

SEM-EDAX

TEM KMnO4 (0.15 g) dissolved in

5 mL of DI water was added

to the above boiling

solution.

Synthesis of graphene/MnO2 composites

GO- 0.05g and MnCl2.4H2O (0.27 g)

were dispersed in isopropyl alcohol

(50 mL), with ultrasonication for 0.5

hr.

85

C

The resulting insoluble slime layer

of Black color precipitate was

formed at the bottom of the flask

Centrifuge at

10,000 rpm for

30 min

Collected

particles

Stability test for MnO2 and GO-MnO2 sensor in

concrete environments a) Cyclic polarization curve and Impedance plot (b) for

GO-MnO2 sensor embedded in concrete environments.

a)

b)

Half-cell potential of rebar embedded in concrete

cube with respect to embeddable sensor and surface

mounted electrode

Potentiodynamic polarization curves for

steel in concrete (a). Embedded sensor

(b).Surface mounted electrode

System Ecorr (mV) Icorr(mA.cm2) Corrosion rate

/(mmpy)

Embedded

(corrosion rate sensor)

MnO2

GO-MnO2

-402 0.0002258 0.002617

-585 0.00025 0.00287

Surface mounted -376 0.0001802 0.00208

Table. Polarizations parameters for rebar embedded in

concrete with respect to embedded sensor and surface

mounted electrode

In the FT-IR spectrum of GO (Fig. 3a), stretches of OH, C-O, it can

be assigned to Graphene sheet. In addition, two broad absorption

bands can be found at 618 cm−1 and 515 cm−1, which are associated

with the coupling mode between Mn-O stretching modes tetrahedral

and octahedral sites.

Conclusions

• In the present study, MnO2 nanorod success fully crystal growth on the graphene sheet by

simple chemical method. The synthesized GO-MnO2 was confirmed by Raman spectra, XRD,

SEM-EDAX and TEM. The resultant products were fabricated by embeddable potential sensor

in concrete structures for corrosion monitoring.

• The stability of sensor in concrete was found to be constant throughout the exposure period of

one month at high alkaline medium.

• Electrochemical studies revealed that GO-MnO2 embeddable sensors always showed higher

half-cell potential values than surface mounted electrodes. This is due to the IR drop problem on

measuring the Half-cell potential.

• Polarization study concluded that, embeddable sensor showed higher Ecorr values than surface

mounted electrodes.

• This is quite suited for our interest to recommend GO-MnO2 sensor is a more reliable sensor for

concrete. This behavior is quite suited to perform as an ideal sensor working under any

environmental conditions.