Electrochemical functionalization of glassy carbon electrode by reduction of diazonium cations in protic ionic liquid

Functionalization of Carbon Materials by Reduction of Diazonium Cations Produced in Situ in a Brønstedt Acidic Ionic Liquid

“…Additional experiments were also performed by varying the concentration of 4‐nitroaniline in [BMIm][HSO 4 ] (5 and 50 m m , respectively), using cyclic voltammetry or chronoamperometry for completing the electrografting. The reported Γ values are in the range 2–10×10 −10 mol cm −2 (see Table S1), and these values are in fairly good agreement with the surface concentration values reported for nitrobenzene grafted layers either in conventional aqueous and organic electrolytes or in other ionic liquids values (reported values in the range 1.5–23×10 −10 mol cm −2 ) . They could be compared to the ideal theoretical value of 12×10 −10 mol cm −2 calculated for a close‐packed monolayer .…”

“…This redox system of rather low intensity does not significantly change during the five subsequent cycles (Figure S1 in the Supporting Information, SI). This behaviour has been already documented in a conventional electrolyte, as well as in an ionic liquid . The appearance of the redox system can be ascribed to the reversible oxidation of hydroxylamine moieties (‐NHOH) to nitroso groups (‐NO) [Eq.…”

“…], resulting from a partial reduction of the nitro substituents of the 4‐nitrobenzene diazonium chemisorbed onto the electrode surface [Eq. ]: …”

“…Four cycles were needed until the corresponding ‐NHOH/‐NO signal centered at 0.3 V (vs. SCE) exhibits a stable current intensity, suggesting that most of the attached nitro moieties have been transformed (Figure ). The signal of the quasi‐reversible oxidation of phenylhydroxylamine to nitrosophenyl groups in aqueous acidic electrolytes is often employed to assess for the grafting of nitrobenzene groups and to estimate the surface concentration of the electrografted organic layer …”

Modification of Carbon Electrode Surfaces

“…Instead of isolating the diazonium salt, it can be prepared in situ by mixing amine with either an acidic aqueous solution of NaNO 2 [36] or tert-butyl nitrite in acetonitrile [37]. Protic ionic liquids (e.g., based on 2-methoxypyridine and trifluoroacetic acid) have also been used recently as electrolytes for the functionalization of carbon surfaces by electrochemical reduction of in situ generated diazonium cations [38]. The protic ionic liquid supplies protons, as in an acidic aqueous medium, required for the generation of the aryldiazonium cation from the corresponding arylamine in the presence of NaNO 2 .…”