3.6.1. Polishing and Cleaning 2663 3.6.2. Vacuum and Heat Treatments 2664 3.6.3. Carbon Electrode Activation 2665 3.7. Summary and Generalizations 2666 4. Advanced Carbon Electrode Materials 2666 4.1. Microfabricated Carbon Thin Films 2666 4.2. Boron-Doped Diamond for Electrochemistry 2668 4.3. Fibers and Nanotubes 2669 4.4. Carbon Composite Electrodes 2674 5. Carbon Surface Modification 2675 5.1. Diazonium Ion Reduction 2675 5.2. Thermal and Photochemical Modifications 2679 5.3. Amine and Carboxylate Oxidation 2680 5.4. Modification by “Click” Chemistry 2681 6. Synopsis and Outlook 2681 7. Acknowledgments 2682 8. References 2682

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Advanced carbon electrode materials for molecular electrochemistry.

Surface chemistry is the topic of this tutorial review. It describes the electrochemical reduction of aryl diazonium salts on carbon, silicon or metals which leads to the formation of an aromatic organic layer covalently bonded to the surface. The method which permits such a modification is set forth. The proof for the existence of the organic layer is brought forward. The grafting mechanism and the covalent bonding between the surface and the aryl group are discussed. The formation of mono or multilayers depending on the experimental conditions is rationalized. Finally some examples of the possible uses of this reaction are given.

Attachment of organic layers to conductive or semiconductive surfaces by reduction of diazonium salts

Electrografting refers to the electrochemical reaction that permits organic layers to be attached to solid conducting substrates. This definition can be extended to reactions involving an electron transfer between the substrate to be modified and the reagent, but also to examples where a reducing or oxidizing reagent is added to produce the reactive species. These methods are interesting as they provide a real bond between the surface and the organic layer. Electrografting applies to a variety of substrates including carbon, metals and their oxides, but also dielectrics such as polymers. Since the 1980s several methods have been developed, either by reduction or oxidation, and some of them have reached an industrial stage. This critical review describes the methods that are used for electrografting, their mechanism, the formation and growth of the layers as well as their applications (742 references).

Electrografting: a powerful method for surface modification

Patterning self-assembled monolayers

This critical review summarizes existing knowledge on the use of diazonium salts as a new generation of surface modifiers and coupling agents for binding synthetic polymers, biomacromolecules, and nanoparticles to surfaces. Polymer grafts can be directly grown at surfaces through the so-called grafting from approaches based on several polymerization methods but can also be pre-formed in solution and then grafted to surfaces through grafting onto strategies including “click” reactions. Several routes are also described for binding biomacromolecules through aryl layers in view of developing biosensors and protein arrays, while the use of aryl diazonium coupling agents is extended to the attachment of nanoparticles. Patents and industrial applications of the surface chemistry of diazonium compounds are covered. This review stresses the paramount role of aryl diazonium coupling agents in adhesion, surface and materials sciences (114 references).

Aryl diazonium salts: a new class of coupling agents for bonding polymers, biomacromolecules and nanoparticles to surfaces

The reduction of diazonium salts in an aprotic medium permits the attachment of substituted aryl groups to a variety of metals:  Co, Ni, Cu, Zn, Pt, and Au. These aryl groups are strongly bonded to the metal as they resist sustained rinsing under sonication in organic solvents. The organic layers have been characterized by cyclic voltammetry, infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, Rutherford backscattering, electrochemical impedance spectroscopy, and atomic force microscopy. From these data it is possible to propose a structure for these grafted layers.

Organic Layers Bonded to Industrial, Coinage, and Noble Metals through Electrochemical Reduction of Aryldiazonium Salts

Electrochemical reduction of aryldiazonium salts (in acetonitrile or acidic aqueous medium) on an iron or mild steel surface permits the strong bonding (which resists an ultrasonic cleaning) of aryl groups on these surfaces. Attachment of aryl groups was demonstrated by the combined used of electrochemistry, infrared spectroscopy and polarization modulation infrared reflection spectroscopy (PMIRRAS), Rutherford backscattering, X-ray photoelectron spectroscopy, and capacity measurements. The substituents of aryl groups, which can be widely varied, include NO2, I, COOH, and long alkyl chains. It is shown that the attachment of the aryl groups is to an iron and not to an oxygen atom and that the bond is covalent.

Marie-Claude Bernard

Papers

Organic Layers Bonded to Industrial, Coinage, and Noble Metals through Electrochemical Reduction of Aryldiazonium Salts

Covalent modification of iron surfaces by electrochemical reduction of aryldiazonium salts.