o9_mohsin - surface functionalization of metal chalcogenides and their bio-organic derivatives
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Surface Functionalization ofMetal Chalcogenides and their
Bio-organic Derivatives
Supervisor :Ass. Professor Dr. Florinel Gabriel Banica.
Muhammad Ali Mohsin.
PhD Student,Deparment of Chemistry.
Norwegian University of Science and
Technology (NTNU), Trondheim,
Norway.
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Outline
Introduction / Background.
What are Chalcogenides?
Surface Modification Methods.
Recent research results.
Properties and Applications.
Potential for improvements.
Conclusion.
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Surface Functionalization
The term surface functionalization denotes a
controlled modification of the surface for the
specialized tasks and applications.i.e;
Catalysis.
Chemical Sensing.
Bio-technology.
Nano-tecnology.
Semiconductors.
Environmental and industrial applications.
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Properties and Applications
As far as a surface modified materials at the nanometer
scale, these can be adapted to build up storage of
information devices or arrays of chemical sensors.
Chalcogenide glasses can be used as active devices
such as fiber amplifiers and lasers.
Transition metal chalcogenide have a wide range of
interesting physical properties (catalysis , lubricants,
semi- and superconducting properties).
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Why metal chalcogenides?
Bio-organic chalcogens derivatives (such as cysteamine, cysteine,
homocysteine) are employed to prepare self-assembled
monolayers on metal surfaces for bio-sensing applications.
The key step is the interaction of the chalcogen moiety with the metal
surface.
Investigation of chalcogen ions (S2-, Se2-) interaction with metals (Au,
Ag, Hg) will substantiate the mechanism of bio-organic derivatives
behaviour in such a process.
NH2
S
S
NH2 O
OH
O
HO
cystine
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Metal Chalcogenides and their
derivatives
Chalcogenide is the collective name ascribed to the
compounds of sulfur, selenium and tellurium.
They play a particular role in nature and living organisms.
Example: the amino acid cysteine contains a thiol group
which can function as anchor bridge for enzyme
immobilization on metal surface.
Metal chalcogenides have relevance for natural aqueous
environment. For example, the iron sulfides constitute a
diverse group of solids and dissolved complexes many
play key roles in marine systems.
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Aims New advances in the thermodynamic and kinetic theory
of electrical reactions involving metal chalcogenides in
the form of molecular layers on the metal electrodesurface.
Investigating the properties of the above-mentioned
compounds by electrochemistry, piezoelectric nano-
gravimetry and surface analysis methods.
Development of new electrochemical methods for the
preparation of metal chalcogenides and their bio-organic
derivatives in various aggregation forms, from surface
mono-layers to nanoparticles.
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Envisaged research methods
Electrochemical methods with liquid and solid electrodes
for performing:
Electrode surface modification by inorganic or organic
layers based on chalcogene derivatives.
Investigation of the physical and chemical properties of the
chalcogenide-based surface layers.
Piezoelectric nano-gravimetry for:
Investigation of the kinetics of the metal chalcogenidegrowth on metal surfaces.
Biosensor applications using electrochemical methods for
the synthesis of the receptor layer.
Surface analysis methods (atomic force microscopy,
photoelectron spectroscopy, micro-Raman spectroscopy)
for investigating chemical structure and composition of
surface layer prepared by electrochemical methods.
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HgS formation and reduction
Effect of deposition potential. 2 M thiourea; pH 6.5; Depos. time, 30 s.
Curves 1 to 6: Ed= 0; 0.02; 0.04; 0.06; 0.08; 0.10 V, respectively.
Two steps experiment
3. Constant potential anodic reaction of Hg in the presence of
thiourea leading to a HgS surface layer
4. Linear potential scan HgS reduction (peak A)
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Reaction scheme
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Recent ResultsA study of mercury sulphide layer formation by anodic polarization of a
mercury electrode at a constant potential in the presence of sulphur
releasing compound, such as thiourea, was carried out.
AIM
This work was aimed to :
Improve the theoretical approach in order to alleviate the effect of errors
resulting from approximations in the theoretical approach.
Improving data processing methods in order to extract relevant kinetic and
thermodynamic parameters.
Assumptions
Consider a reversible electron transfer reaction coupled with chemical
reaction at equilibrium, such as;
Critical assumption in this derivation was invariability of the surface activi
of the mercury sulphide.
HgS + n e- Hg + S-2
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Previous theoryAn available approximation theoretical approach for the electrochemical
reaction of a mercury sulphide surface layer was previously developed[1,2]. According to this theory following relationship was obtained :
Eq. 1
2. J. P. Haberman, PhD Thesis, University of Wisconsin, 1967.
3. F. G. Banica, M. Galk, I. Svancara, K. Vytras, Electroanalysis2009, 21, 332.
Ep = peak A potential
Eo = formal potential for HgS reduction
Qt = total charge consumed in HgS reduction
v= potential sweep rate
A = electrode surface area
D = diffusion coefficient of S(2-)
n= number of electrons per HgS molecule
F= Faraday constant
T= absolute temperature
MAIN DRAWBACK: the approximation of constant HgS amount does
not hold at E= Ep
ln ln ln( )
2 p o p
R T R T R T E E v Q A R T nFD E
nF nF nF
= - - +
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New equations
Eq.3
Eq.2
Where:
i= current measured at the potential E
Q = amount of electricity consumed by HgS reduction up till thepotential E
ADVANTAGE: this approach involves iand Qvalues atE>>Ep where the approximation of invariable HgS
amount is fairly fulfilled.
3 4ln ln ( / )i k k Q nF R T E = + -
3 20.5lnk k v= +
5ln 0.5 ln ( / )Q k v nF R T E = - -
5 ln( ) 0.5 ln( / ) ( / ) ok FA nR T D F nR T F E = + +
4k =an empirical fitting const.
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Data analysis method
Three-dimensional data plot and fitting based on
Equations 2 and 3.
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Results: lniplot vs. Eand ln(Qt)(Eq. 2)
Figure 1. Thiourea, 1.0 M; deposition time, 100; 150; 200; 250;300; 350; 400; 450; 500; 550; 600 s; scan rate, 0.02 V/s.
Conclusion: Very good fit; fair agreement between theoretical andexperimental fitting parameters
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Results: 3D Plot of lnQ vs. lnvand E
Figure 2. Data fitting according to Equation (3). Experimentalconditions as in Figure 1.
Conclusion: Some deviations from predicted behavior. Theoryrefinement is needed.
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Next steps
Improving the theoretical approach.
Investigating mercury selenide.
Investigating mercury salts with bio-thiols (cysteine and
its derivatives and analogous, including seleno-cysteine).
Investigating analogous Ag compounds by
electrochemistry, piezoelectric nano-gravimetry and
surface analysis methods.
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Conclusion
This work focuses on inorganic and bio-organic
derivatives of two chalcogenides elements, namely sulfur
and selenium and aims at investigating the interaction ofchalcogenide ions and derivatives with metal ions.
Thanks to:
Associate Prof.Dr.Florinel Gabriel Banica.
University of Bartislava and Summer School organizers.
Norwegian University of Science and Technology.
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Thank you for your
kind attention!
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