Adsorption thermodynamics and kinetics study for the self-assembly of 1,8,15,22-tetraaminophthalocyanatocobalt(II) on glassy carbon surface

作者：Sivanesan Arumugam; John S Abraham^*

来源：Electrochimica Acta, 2009, 54(28): 7458-7463.

DOI：10.1016/j.electacta.2009.07.081

• alpha-Tetraaminophthalocyanatocobalt(II)
• Self-assembled monolayer
• Cyclic voltammetry
• Frumkin adsorption isotherm
• Raman spectroscopy

Spontaneous adsorption of 1,8,15,22-tetraaminophthalocyanatocobalt(II)(4 alpha-Co(II)TAPc) on glassy carbon (CC) electrode leads to the formation of a stable self-assembled monolayer (SAM). Since the SAM of 4 alpha-Co(II)TAPc is redox active, its adsorption on GC electrode was followed by cyclic voltammetry. SAM of 4 alpha-Co(II)TAPc on GC electrode shows two pairs of well-defined redox peaks corresponding to Co(III)/Co(II) and Co(III)Pc(-1)/Co(III)Pc(-2). The surface coverage (Gamma) value, calculated by integrating the charge under Co(II) oxidation, was used to study the adsorption thermodynamics and kinetics of 4 alpha-Co(II)TAPc on GC surface. Cyclic voltammetric studies show that the adsorption of 4 alpha-Co(II)TAPc on GC electrode has reached the saturation coverage (Gamma(s)) within 3 h. The Gamma(s) value for the SAM of 4 alpha-Co(II)TAPc on GC electrode was found to be 2.37 x 10-(10) mol cm(-2). Gibbs free energy (Delta G(ads)) and adsorption rate constant (k(ad)) for the adsorption of 4 alpha-Co(II)TAPc on GC surface were found to be -16.76 kJ mol(-1) and 7.1 M(-1) s(-1). respectively. The possible mechanism for the self-assembly of 4 alpha-Co(II)TAPc on GC surface is through the addition of nucleophilic amines to the olefinic bond on the GC surface in addition to a meager contribution from pi stacking. The contribution of pi stacking was confirmed from the adsorption of unsubstituted phthalocyanatocobalt(II) (CoPc) on GC electrode. Raman spectra for the SAM of 4 alpha-Co(II)TAPc on carbon surface shows strong stretching and breathing bands of Pc macrocycle, pyrrole ring and isoindole ring. Raman and CV studies suggest that 4 alpha-Co(II)TAPc is adopting nearly a flat orientation or little bit tilted orientation.

• 出版日期2009-12-1