1. Sensor development exploiting graphite-epoxy composite as
electrode material
A. L. M. Azevedo, R. S. de Olive ira, E. A. Ponzio, F. S. Semaan
Composite materials: mixtures of two or more components with different
properties and distinct boundaries between them.
Homogeneous macroscopic levels,
Heterogeneous at microscopic levels.
Milton, G. W. Theory of composites. Cambridge University Press. 2004. Cambridge. 719p.
Sensors Composites: mixture of at least one phase conductor and
insulator, reaching a different material.
Versatility, moldability, stability, possibility of modification, surface renewal
ease, at low cost.
Applicability to diverse environments of analysis and wide range of potential.
Adams R. Carbon Paste Electrodes. Analytical Chemistry, Julho de 1958.
INTRODUCTION: Since the first studies reported by Adams [1], composite sensors have been explored in electroanalysis due
to their advantages compared with metal electrodes. They consist of a dispersion of at least one phase conductor in an
insulating component, generating a new material. By far the most reported for conductive phase is carbon in its many forms
available, with different composites described according to their insulating phases. Such composites were prepared by
mechanical dispersion of suitable amounts of graphite powder (Sigma-Aldrich, USA, 2-20 mM) in epoxy resin (Avipol, Brazil,
2126-3024 Silaex SQ), being then let to cure for at least 24 hrs under pressure and polished with suitable tools.
Work electrode
Surface
catalytic
Analytical signals directly dependent not only on the surface area,
but also the possibility of adsorption.
Brett, A. M. O.; Brett, C. M. A. Electroquímica: princípios, métodos e aplicações. Editora
Almedina. Coimbra. 471 p.
Preliminary studies:
Proportions of polymer and catalyst. In this study, the epoxy resin
(Avipol, Silaex 2126-3024 SQ, Brazil).
Technique for the homogenization of the composite.
Catalytic surface to be developed.
Ideal ratio of composite. Tests to qualify the best composite
graphite epoxy.
Universidade Federal Fluminense, Instituto de Química, Niterói RJ, Brasil
e-mail: andreazevedo@id.uff.br, felipesemaan@gmail.com
Advaced studies:
The composite set of best features, other tests were administered:
Friability (the condition of being friable) is the ability of a solid substance
to be reduced to smaller pieces with little effort. Comparison test between
the raw materials and developed new composite. Mass loss was 0.75%.
Excluding the white reduction was 0.3% .
Hardness at first trials were carried out in an apparatus for tablets.
Showed that the composite has a hardness negligible, compared to the
source material.
Hardness Vickers (HV), more specific hardness test to determine the
hardness of materials shown how the composite is soft.
Atomic force microscopy (AFM)
0.0 0.5
-50
0
50
25 mV/s
Electrode 1
Electrode 2
Electrode 3
Electrode 4
GCE
Current (A)
E / V vs Ag|AgCl
Comparative composite X Glassy Carbon
Figure 5: Comparate among composite and to a glassy carbon commercial
electrode with almost same geometrical surface
-0.3 0.0 0.3 0.6 0.9
-100
-50
0
50
100
E / V vs Ag|AgCl
2mV*s-1
5mV*s-1
10mV*s-1
20mV*s-1
50mV*s-1
100mV*s-1
I (A)
Electroative area
Figure 4: . Cyclic voltammograms obtained with the 65% (graphite, w/w) on
5.0 mmol l-1 hexacyanoferrate in 0.5 mol l−1 KCl at different scan rates from
2 to 100 mV s-1.
Topography – Scan forward Line fit Topography – Scan forward Line fit
Figure 3a.: Topography obtained obtained with the 65% (graphite, w/w).
Figure 3b.: 3D projection topography acquired.1
(a) (b)
A suitable stable and low cost material for electroanalytical application is
hereby described. Its hardness facilitates polishing, and subsequently
recovery of the surface, allowing stable but transient chemical modifications
as well as renewal.
The methodology of polishing on abrasive surface resulted on low
roughness topography.
Economically such material showed to be easy to build and cost-effective
when compared to glassy carbon commercially available sensors.
For analytical purpose such composite is being evaluated as substrate for
gold-nanoparticles immobilization in chitosan-modified and cellulose
acetate films, with good preliminary results.
The electrochemical cell developed can be directly used to determinate
many inorganic and/or organic compounds in real samples or even
undergoes to chemical modification to more specialized situations.
Acknowledgments
References
Conclusion
[1] R. N. Adams, Anal. Chem. 30 (1958) 1576.
[2] K. Kalcher, J.M. Kauffmann, J. Wang, I. Svancara, K. Vytras, C. Neuhold, Z.
Yang, Electroanalysis 7 (2009) 598-656.
[3] R. Pauliukaite, M. E. Ghica, O. F. Filho, C. M. A. Brett. Anal. Chem. 81
(2009) 5364-5372.
Electroative area
Table 1.: Different compositions were prepared (55-80% w/w) and
characterized by thermogravimetry analysis (TGA-DTA) and cyclic
voltammetry (CV).
55 60 65 70 75 80
0.0
0.1
0.2 Anodic
Catodic
GRAPHITE (m m -1)
ELECTROATIVE AREA(cm2)
Figure 2: Thermal analysis of different compositions
55 60 65 70 75 80
0.1
0.2
0.3
0.4
Roughness (rms)
Graphite (%)
Table 2: Calculated roughness (rms) found by AFM results and topography
(Tapping mode)
0 20 40 60 80 100 120
(a)
(b)
2 Theta / 
(c)
Figure 5: XDR for Graphite powder in (a), Epoxy in (b) and Grahite/Epoxy 65%
composite in (c).
6 cm
3,1 mm
Internal diameter
External diameter
3,3 mm
(a) (b)
Figure 7a: Body of working electrode
Figure 7b: Arrangement of electrodes in electrochemical cell
One disposable electrochemical cell comprising working electrode
(composite described), counter electrode of stainless steel, silver
conductive epoxy reference (pseudo-reference) electrode was constructed.
The electrodes were mounted on a plunger of a 5 mL syringe, being then
the syringe filled by insulating polymers for mechanical purposes.