Immobilization of [Cu(bpy)2]Br2 complex onto a glassy carbon electrode modified with α-SiMo12O404− and single walled carbon nanotubes: Application to nanomolar detection of hydrogen peroxide and bromate

doi:10.1016/j.aca.2009.01.007

Analytica Chimica Acta

Volume 635, Issue 1, 2 March 2009, Pages 63-70

https://doi.org/10.1016/j.aca.2009.01.007 Get rights and content

Abstract

A simple procedure has been used for preparation of modified glassy carbon electrode with carbon nanotubes and copper complex. Copper complex [Cu(bpy)₂]Br₂ was immobilized onto glassy carbon (GC) electrode modified with silicomolybdate, α-SiMo₁₂O₄₀⁴⁻ and single walled carbon nanotubes (SWCNTs)_. Copper complex and silicomolybdate irreversibly and strongly adsorbed onto GC electrode modified with CNTs. Electrostatic interactions between polyoxometalates (POMs) anions and Cu-complex, cations mentioned as an effective method for fabrication of three-dimensional structures. The modified electrode shows three reversible redox couples for polyoxometalate and one redox couple for Cu-complex at wide range of pH values. The electrochemical behavior, stability and electron transfer kinetics of the adsorbed redox couples were investigated using cyclic voltammetry. Due to electrostatic interaction, copper complex immobilized onto GC/CNTs/α-SiMo₁₂O₄₀⁴⁻ electrode shows more stable voltammetric response compared to GC/CNTs/Cu-complex modified electrode. In comparison to GC/CNTs/Cu-complex the GC/CNTs/α-SiMo₁₂O₄₀⁴⁻ modified electrodes shows excellent electrocatalytic activity toward reduction H₂O₂ and BrO₃⁻ at more reduced overpotential. The catalytic rate constants for catalytic reduction hydrogen peroxide and bromate were 4.5(±0.2) × 10³ M⁻¹ s⁻¹ and 3.0(±0.10) × 10³ M⁻¹ s⁻¹, respectively. The hydrodynamic amperommetry technique at 0.08 V was used for detection of nanomolar concentration of hydrogen peroxide and bromate. Detection limit, sensitivity and linear concentration range proposed sensor for bromate and hydrogen peroxide detection were 1.1 nM and 6.7 nA nM⁻¹, 10 nM–20 μM, 1 nM, 5.5 nA nM⁻¹ and 10 nM–18 μM, respectively.

Introduction

Among diverse techniques developed for quantitative determination, electrochemical methods are appear to have most potential applications due to their high sensitivity and simplicity. Direct oxidation or reduction of analytes at bare electrodes are irreversible and require high overpotential [1]. This high overpotential results in electrode fouling, poor reproducibility, low selectivity and poor sensitivity. Over the past decades there has been a continued interest in reducing overpotential with modification of electrode surfaces [2]. The alternating deposition of bipolar cationic and anionic compounds and formation of multilayer structures is a successful method for fabrication of ultrathin films with thickness at the nanometer scale [3], [4], [5].

Different cationic species such as transition metal complexes, [Fe(bpy)₃]²⁺[6], methaloporphyrine [7], [Cu(bpy)₂]²⁺[8], [Ru(bpy)₃]³⁺[9], [Os(bpy)₃]³⁺[10], cationic surfactants [11] metalodendrimers [12], [13] polymeric materials, poly(new fuchsin) [14] poly osmium functionalized pyrrole [15] and poly (diallyl dimethyl ammonium chloride) [5] have been used for formation of bilayer or multilayer film with various POMs. Due to electrochemical reversibility, catalytic and electrocatalytic activity and drug properties of copper complexes, they have been used for preparation of organic–inorganic hybrid materials with various POMs [16], [17], [18], [19], [20]. Multilayer films of POMs and cationic compounds adsorbed irreversibly on the surface of different electrodes such as, GC [9], [10], [12], [15], wax impregnated graphite [11], indium thin oxide [5], Au [21] and carbon paste [8]. As reported in the literature, different supporting carbon materials have been used to disperse and stabilize electron transfer mediators, due to their low background currents, wide potential windows, chemical inertness and low cost [22].

Due to the unique properties of CNTs such as excellent electrical conductivity, high surface area, chemical stability and significant mechanical strength [23], [24] application of carbon nanotubes for fabrication of electrochemical sensors and biosensors were investigated [25], [26], [27], [28], [29], [30], [31]. CNTs can also facilitate electron transfer to reactive sites, and they are attractive materials for catalytic supports in electrochemistry. Recently many efforts have been focused on the functionalization of carbon nanotubes with various molecules, using covalent and non-covalent approaches [32]. Non-covalent method is an effective way to preserve the sp² nanotube structure and their electronic characteristics. Immobilizations of molecules and biomolecules onto CNTs have been used as new strategy for fabrication sensor and biosensors [32], [33], [34], [35]. Furthermore, the stability and electrochemical super-capacity of polyoxometalates increased when they immobilized onto electrode surfaces modified with CNTs [36], [37], [38], [39], [40].

Due to stability of GC electrode modified with CNTs and POMs, in the present study this nanocomposite was used for immobilization of electroactive Cu-complex, [Cu(bpy)₂]²⁺. The modified electrode shows more stability due to electrostatic interactions between copper complex and silicomolybdate. Furthermore this system exhibits clear electrochemical redox activity for both POMs and Cu-complex at wide pH range. The copper complex immobilized onto CNTs/POMs film shows excellent electrocatalytic activity towards bromate and hydrogen peroxide reduction in acidic solution.

In comparison to CNTs/[Cu(bpy)₂]²⁺ electrode the CNTs/POMs/Cu-complex modified electrode show more stable electrochemical properties and electrocatalytic activity. In addition the modification method, stability and electrocatalytic activity of adsorbed copper complex-film is comparable or even better than other procedures used for modification of electrodes with copper compounds, such as GC electrode modified with DNA–Cu²⁺ complex [41], graphite electrode modified with copper complex [42], gold electrode modified with Cu-phthalocyanine [43], Cu²⁺-complex at La(III) hydroxide nanowires modified carbon paste electrode [44], carbon ceramic electrode modified with Cu-complex [45], copper(II)-oxide nanorods [46], CuO nanowires [47] and carbon paste electrode containing copper microparticles [48]. Finally the modified electrode was successfully used for nanomolar detection of hydrogen peroxide and bromate, using hydrodynamic amperometry technique.

Section snippets

Chemical and reagents

α-Silicon polyoxomolybdate, α-SiMo₁₂O₄₀⁴⁻ was from Sigma and used without further purification. The [Cu(bpy)₂] Br₂ was synthesized, purified and characterized as previously reported [49]. NaBrO₃, acetonitrile (ACN), dimethyl sulfoxide(DMSO), H₂O₂ and other reagents were of analytical grade from Merck, Fluka and Aldrich used as received. Single walled carbon nanotubes (SWCNTs) was from Sigma. The purity of CNTs was 90%., with surface specific area of 480 m² g⁻¹, diameter of 1–2 nm and 0.5–2 μm

Deposition of [Cu(bpy)₂]Br₂ and α-SiMo₁₂O₄₀⁴⁻ onto CNTs modified GC electrodes

Cyclic voltamograms of GC/CNTs/[Cu(bpy)₂]²⁺_, GC/CNTs/α-SiMo₁₂O₄₀⁴⁻ and GC/CNTs/α-SiMo₁₂O₄₀⁴⁻/[Cu(bpy)₂]²⁺ modified electrodes were recorded in pH 1 buffer solution (Fig. 1). As shown a reversible redox couple (formal potential E⁰′ = 0.065 V) for copper complex (Cu(II)/Cu(I)) was observed (voltammogram A). Co-immobilization of the SWCNTs and α-SiMo₁₂O₄₀⁴⁻ on the GC electrode showed three well defined redox couples (formal potentials (E⁰′) of 0.24, 0.13 and −0.077 V) (voltammogram B). As we can see,

Conclusion

Mono layer of silicomolybdate adsorbed onto electrode surface modified with CNT and used as inorganic template for stable adsorption of cationic copper-complex [Cu(bpy)₂]²⁺. Due to electrostatic attraction between anions and cations the stability of adsorbed heteropolyanionin and Cu-complex increased to higher pH values pH < 7. Adsorbed [Cu(bpy)₂]²⁺ complex shows well defined redox couple. Furthermore, this redox couple shows excellent electrocatalytic activity for reduction of bromate and

Acknowledgments

This research was supported by Iranian Nanotechnology Initiative and Research Office of University of Kurdistan.

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Immobilization of [Cu(bpy)2]Br2 complex onto a glassy carbon electrode modified with α-SiMo12O404− and single walled carbon nanotubes: Application to nanomolar detection of hydrogen peroxide and bromate

Abstract

Introduction

Section snippets

Chemical and reagents

Deposition of [Cu(bpy)2]Br2 and α-SiMo12O404− onto CNTs modified GC electrodes

Conclusion

Acknowledgments

Bioelectrochem.

Electrochem. Commun.

J. Electroanal. Chem.

J. Mol. Struct.

Anal. Chim. Acta

J. Electroanal. Chem.

J. Electroanal. Chem.

J. Mol. Struct.

Inorg. Chem. Commun.

J. Solid. State. Chem.

J. Electroanal. Chem.

Carbon

Electrochim. Acta

Anal. Biochem.

Electrochem. Commun.

Electrocim. Acta

Electrochem. Commun.

Anal. Chim. Acta

Electrochim. Acta

Sens. Actuators B

Inorg. Chim. Acta

Talanta

J. Electroanal. Chem.

J. Electroanal. Chem.

J. Power Sources

Biosens. Bioelectron.

Anal. Chem.

Chem. Mater.

Immobilization of [Cu(bpy)₂]Br₂ complex onto a glassy carbon electrode modified with α-SiMo₁₂O₄₀⁴⁻ and single walled carbon nanotubes: Application to nanomolar detection of hydrogen peroxide and bromate

Deposition of [Cu(bpy)₂]Br₂ and α-SiMo₁₂O₄₀⁴⁻ onto CNTs modified GC electrodes