O9_Mohsin - Surface Functionalization of Metal Chalcogenides and Their Bio-Organic Derivatives

8/3/2019 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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O9_Mohsin - Surface Functionalization of Metal Chalcogenides and Their Bio-Organic Derivatives

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