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Chemically Modified Electrodes (CMEs)
- Modification of Monolayers and Their Applications
State Key Laboratory of Electroanalytical Chemistry
Changchun Institute of Applied Chemistry
Chinese Academy of Sciences
Nov.5, 2003
Contents
• History and Development of CMEs
• Classification of CMEs
• Orientated Monolayer & Classification of Kaleidoscopic SAMs
• Several Examples
Nov.5, 2003
Early Studies on CMEs
1. Early of 1970’s, F.C. Anson (CalTech), theory of chemical adsorption and adlayer structure.
2. 1973, R.F. Lane (Hawaii) & A.T. Hubbard (Cincinnati), olefin derivatives at Pt surface.
3. 1975, L.L. Miller (Colorado State), asymmetric reagent for preparing chiral electrode,
electrosynthesis of optical rotation substance, electrode-selective reaction.
4. R.W. Murray (North Carolina), Covalent modification,
metal oxide (SnO2) + silicane - monolayer modification.
5.T. Kuwana (Ohio State), Cyanourea Acyl Chloride/Graphite
Nov.5, 2003
Classification of CMEs
Chemically Modified Electrodes (CMEs)
Composite & Others
Polymer
Rotating
Dropping
Dipping
Radiation Polymerization
Plasma Polymerization
Chemical Polymerization
By Chemical Synthesis Simply by Physical/
Chemical Adsorption
Electrochemical Polymerization
Carbon Series
Metal Oxide & Semiconductors
Irreversible Adsorption
Underpotential Deposition (UPD)
LB & SA Films
Monomer
Electrodeposition
Vapor Deposition
Polymer Thin Film
Adsorption
Covalent Bonding
Multilayer
Monolayer
Nov.5, 2003
Merit: Function & Structure - tunable & controllable
Applications:
Electrosynthesis & Electrocatalysis
ChemiSensors & Biosensors
Electroanalysis & Electrochemical Detection
Electrolyzing, Electroplating & Fuel Cell
The understanding of the interrelationship between the molecular structure of amphiphiles and
their organization on different surfaces is a fundamental problem. The packing and orientation of
such molecules affect the surface chemistry of the monolayer, and play an important role in the
phenomena of boundary lubrication, corrosion inhibition, adhesion, and catalysis.
Nov.5, 2003
Orientated Monolayer
Origin of the oil-on-water and LB film,
1. Aristotle - spread oil droplets on a water surface and used the behavior of the film to foretell the future.
2. 1774, Benjamin Franklin, the first preparation of LB film, and show the thickness of the oil layer is
a few nanometers.
3. 1891, Agnes Pockels, the first monolayers at the water-air interface.
4. 1899-1913, Rayleigh, Devaus, and Hardy, the nature of these layers, and the amphiphilic structure.
5. 1917, Langmuir, the first systematic study of monolayers of amphiphilic molecules
at the water-air interface.
6. 1935, Blodgett, the first study on a deposition of multilayers of long chain carboxylic acid
onto a solid substrate.
Deposition of a monolayer from the water-air interface to a vertical plate.
Nov.5, 2003
Self-Assembled Monolayers
Classical SAM literatures,
1. Bigelow , W.C.; Pickett,D.L.; Zisman, W.A. J. Colloid Interface Sci. 1946, 1, 513.
2. Zisman, W.A. Adv. Chem. Ser. 1964, 43, 1.
3. Sagiv, J. J. Am. Chem. Soc. 1980, 102, 92.
Several typical examples of organic monolayers
Organosilicon/Hydroxylated surfaces (SiO2/Si, Al2O3/Al, Glass, etc.)
Alkanethiols/Au, Ag, Cu
Dialkyl sulfides, dialkyl disulfides/Au
Alcohols, amines, pyridines/Au, Pt
Carboxylic acids/Al2O3, Ag (acid-base interaction --> salt)
Si
O
O
Si
O
O
Si
O
O
Si
O
O
Si
O
O
O
SiO, SiO2, Al2O3, SnO2, GeO, TiO2 & ZnSe
S
Si
S......S
S
Au
S
N
S
S
S
Self-assembled monolayers are molecular assemblies that are formed spontaneously by the immersion of an
appropriate substrate into a solution of an active surfactant in an organic solvent.
Nov.5, 2003
Self-Assembled Monolayers
Electroactive Groups in SAMs
Surface group
Ferrocene
Alkyl, or derivatizedalkyl group
Viologen
Quinone
Interchain van der waals
and electrostatic interactions
Surface-active
headgroup
Chemisorption
Surface
Porphyrin
Bioactive Molecules in SAMs
Electroactive Biomolecules in SAMs
Inorganic composites and particles in SAMs
A schematic view of the forces in a self-assembled monolayer
Polymers in SAMs
Nov.5, 2003
Extended SAM Systems
Small Organic Molecules
-Classical SAMs
I-/I
S2-/Sca.1SCN-
NSCCN-
Metal Atoms
UPD of Ag, Cu, Ni, Pb, etc.
Bulk Chain
Different Headgroups, eg. -SH, Pyridyl, etc.
Non-conjugated
Conjugated Chain
Charged negatively, or positively
Neutral
Tail group
Inorganic Ions/Atoms
(unconventional SAM systems)
Headgroup
Nov.5, 2003