Electrochemical Preparation and Characterization of Silicotungstic Heteropolyanion Monolayer Electrostatically Linked Aminophenyl on Carbon Electrode Surface

Abstract

In this paper, an organic−inorganic composite film of heteropolyanion was formed by attaching a Keggin-type heteropolyanion, SiW12O40 4-, on carbon electrode surface derivatized by 4-aminophenyl monolayer. The composite film thus grafted on carbon electrode surface has good stability because of the ionic bonding character between SiW12O40 4- and surface aminophenyl groups. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used to characterize the composite film. Compared with SiW12O40 4- electrodeposited on a bare glassy carbon electrode (GCE), the composite film gives three more sharp and well-defined redox couples attributed to two one- and two-electron processes, and the analyses of the voltammograms of SiW12O40 4- anion in the composite film modified on GCE shows that its surface coverage is close to a closest packing monolayer. STM characterization shows that a two-dimensional order heteropolyanion monolayer was formed on HOPG substrate. The composite film provides a favorable environment for electron and proton transfer between SiW12O40 4- ion and electrode surface, which may make it suitable for various applications in sensors and microelectronics devices.

Electrochemically Assisted Covalent Modification of Carbon Electrodes

“…Potential scanning in an acidic solution of 12-tungstosilicic acid resulted in formation of SiW 12 =aminophenyl modi®ed electrodes, in which electrostatic interactions are proposed to lead to electrodeposition of the inorganic layer. STM and XPS analyses of modi®ed HOPG surfaces con®rmed the formation of an ordered, compact monolayer of heteropolyanions [38]. At pH less than 2, the modi®ed electrode has good stability and catalyzes the electroreduction of nitrite [18].…”

“…Carbon electrodes modi®ed via the diazonium reduction method have been carefully investigated and characterized. XPS [2, 9, 26±31, 36±38] Rutherford backscattering (RBS) [26], polarization modulation IR re¯ection absorption spectroscopy [26], Auger spectroscopy [26], unenhanced Raman spectroscopy [30± 32, 36, 37], scanning tunneling microscopy (STM) [26,35,38] and scanning force microscopy (SFM) [35] have been used for surface analysis.…”

“…The differential pulse voltammetry (DPV) of ferrocenemonocarboxylic acid (FCA) has been examined at GC electrodes Co(II)TPP [b] [21] electrochemical reduction in protic medium [2,18,26,27,29,30,38] (i) electrochemical reduction in protic medium [2,26,27] (ii) (i) electrochemical reduction in protic medium [18,38] (ii) SiW 12 [27] conc. HNO 3 H 2 SO 4 nitrated product [27] modi®ed with tetraethylene glycol diamine [8].…”

“…Liu, Shi, and Dong used the diazonium reduction method as the ®rst step towards constructing stable heteropolyanion-modi®ed electrodes [18,38]. Nitrophenyl modi®ed GC, HOPG and carbon ®ber microdisk array electrodes were reduced to give aminophenyl modi®ed surfaces.…”

Covalent modification of a glassy carbon surface by electrochemical oxidation of r-aminobenzene sulfonic acid in aqueous solution

“…In general, there are two main methods for modifying the carbon surface through free radical grafting. One is covalent modification of carbon surfaces by aryl radicals generated from the electrochemical reduction of diazonium salts in acetonitrile solution [8][9][10][11][12][13][14][15]. The other is the electrochemical oxidation of various amine-containing compounds in absolute ethanol or acetonitrile solution [16][17][18][19][20][21][22][23][24][25] to lead to amine cation radicals which form covalent C-N bonds with the carbon surfaces and the modifying layer is shown to be a compact packing monolayer of amino group [16,17].…”