Graphene-MnO 2 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: [email protected] 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 MnO 2 (GO-MnO 2 ) 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 MnO 2 nanorods are monodispersed on Graphene surface. Graphene modified MnO 2 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-MnO 2 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 MnO 2 and GO-MnO 2 were obtained by simple chemical method. These diffraction peaks of synthesized MnO 2 and GO-MnO 2 were similar to tetragonal crystal phase of MnO 2 (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 MnO 2 and GO-MnO 2 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 sp 2 domains increases during reduction of GO. Moreover, the similar MnO 2 peak at 621.41 cm − 1 was observed both samples. a) b) 2 4 6 8 10 12 14 keV 0 1 2 3 4 5 6 7 cps/eV Mn Mn O C 2 4 6 8 10 12 14 keV 0 1 2 3 4 5 6 7 8 cps/eV Mn Mn O C MnO 2 ) GO-MnO 2 ) The morphology of the as synthesized MnO 2 and GO- MnO 2 nanostructure is shown in Fig. Fig a is an bright field TEM image of the MnO 2 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 MnO 2 nanorods , to observed two lattice fringe with a d-spacing of 0.32nm and 0.71nm, corresponds to 101 and 111 of MnO 2 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 MnO 2 structure. More over, the edge of the graphene sheet represented the TEM image. There is no significant observed that morphology of the MnO 2 nanorods. The similar MnO 2 lattice fringe was observed on the GO- MnO 2 nano composite. Morphological study revealed that the MnO 2 nanorod crystal growth on the graphene sheet. a) TEM image of the MnO 2 nanorod and (b) GO-MnO 2 nanocomposite b) a) TEM observation FTIR spectra Raman spectra XRD SEM –EDAX observation A structure of GO-MnO 2 electrode. Sensors assembled in concrete structures Analytical characterization FT-IR, Raman spectra, XRD pattern, SEM-EDAX TEM KMnO 4 (0.15 g) dissolved in 5 mL of DI water was added to the above boiling solution. Synthesis of graphene/MnO 2 composites GO- 0.05g and MnCl 2. 4H 2 O (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 MnO 2 and GO-MnO 2 sensor in concrete environments a) Cyclic polarization curve and Impedance plot (b) for GO-MnO 2 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 E corr (mV) I corr (mA.cm 2 ) Corrosion rate /(mmpy) Embedded (corrosion rate sensor) MnO 2 GO-MnO 2 -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, MnO 2 nanorod success fully crystal growth on the graphene sheet by simple chemical method. The synthesized GO-MnO 2 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-MnO 2 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 E corr values than surface mounted electrodes. • This is quite suited for our interest to recommend GO-MnO 2 sensor is a more reliable sensor for concrete. This behavior is quite suited to perform as an ideal sensor working under any environmental conditions.