Polyazulene-Based Materials for Heavy Metal Ion Detection. 3. (E)-5-((6-t-Butyl-4,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole-Based Modified Electrodes

Abstract

A recently synthesized azulene-tetrazole molecular receptor is proposed in this paper to continue the series of azulene substituted compounds that have been developed to build polyazulene-based materials for heavy metal (HM) ion detection. This study focuses on characterization of (E)-5-((6-t-butyl-4,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L) by electrochemical techniques in view of its use for designing electrochemical sensors for HM ion complexation. The character of redox processes was proved by cyclic, differential pulse, and rotating disk electrode voltammetry. An in-depth thermodynamic study of the complexation properties of the free ligand with Pb(II) and Cd(II) from aqueous solutions was performed, and the stoichiometry and stability constant values were determined. Chemically modified electrodes (CMEs) based on L (L-CMEs) prepared by controlled potential electrolysis (CPE) at different applied potentials and charges were characterized by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Their surface morphology was examined by scanning electron microscopy (SEM). The complexing properties of L-CMEs were investigated towards the detection of HM ions by anodic stripping and compared to the stability constants of the complexes in solution. Voltametric curves showed well-defined peaks for Pb (II), Cd (II), Cu (II) and Hg (II), but the responses differ from each other and vary depending on the ion concentrations in the accumulation solutions. The best results were obtained for Pb(II) and Cd(II) ions. The results obtained for Pb(II) are promising and can be used for its analysis in water solutions (detection limit of about 10−9 M).

Polyazulene Based Materials for Heavy Metal Ions Detection. 4. Search for Conditions for Thiophen-Vinyl-Pyridine-Azulene Based CMEs Preparation

“…Most azulene derivatives present an irreversible electrooxidation leading to polymers. CMEs obtained in this way can be used to build electrochemical sensors, as shown in our previous works [6,7]. This straightforward approach is not common in the attempt of trace metals detection.…”

“…This straightforward approach is not common in the attempt of trace metals detection. Some examples can be mentioned [7][8][9][10]. CMEs with complexing properties are alternative tools for the recognition of HMs ions, which is usually done by very sensitive methods, as follows: inductively coupled mass spectrometry [11], atomic absorption spectroscopy [12], cold vapor atomic fluorescence spectrometry [13], and emission spectroscopy [14].…”

“…CMEs with complexing properties are alternative tools for the recognition of HMs ions, which is usually done by very sensitive methods, as follows: inductively coupled mass spectrometry [11], atomic absorption spectroscopy [12], cold vapor atomic fluorescence spectrometry [13], and emission spectroscopy [14]. Electrochemical techniques have received attention and have promising applications for biological and environmental analysis, due to their low cost, simplicity, sensitivity, selectivity, and fast response [7][8][9][10]15]. To get complexing CMEs, the most efficient preparation is the direct electropolymerization of a complexing monomer [16].…”

“…For instance, the azulene-tetrazoles gave very good results in HMs detection. CMEs based on E-5-((6-t-butyl-4,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L1) were prepared on glassy carbon electrode [7]. The ability of L1-CMEs to complex Cd(II), Pb(II), Cu(II) and Hg(II) cations in aqueous solutions with concentrations between 10 −9 and 10 −4 M has been proved.…”