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

Laura-Bianca Enache,Eleonora-Mihaela Ungureanu,Marius Enăchescu,Veronica Anăstăsoaie,Ovidiu-Teodor Matica,Cristina-Andreea Amarandei,Cecilia Lete,Jérémy Brandel,Alina Giorgiana Brotea

doi:10.3390/sym13091642

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).

Highlights

For human safety, it is extremely important to monitor the heavy metal (HM) ions that are present in water and food [1,2,3,4]
Electrochemical sensors based on Chemically modified electrodes (CMEs) [8] could bring more sensitivity and selectivity in comparison to other spectroscopic or optical techniques [9]
Considering the advantages of CMEs and our goal of detecting HMs, it is important to search for new molecules that lead to the obtention of new types of sensors

Summary

Introduction

It is extremely important to monitor the HM ions that are present in water and food [1,2,3,4]. Electrochemical sensors based on CMEs [8] could bring more sensitivity and selectivity in comparison to other spectroscopic or optical techniques [9] They can be included in portable devices allowing on-site monitoring of HMs. The combination of modern electrochemical techniques with developments in the field of microelectronics and miniaturization allows the introduction of high-performance and reliable electrical devices for efficient control of processes or pollution. Considering the advantages of CMEs and our goal of detecting HMs, it is important to search for new molecules that lead to the obtention of new types of sensors To make this possible, they must contain a metal ion complexing unit and a moiety that is capable of electropolymerization [11,12]. Irreversible followed by polymerization reactions leading to a polymeric film, as has been seen in case of other azulene compounds [13,15]

Method

Recognition of Heavy Metal Ions Using L-CMEs