Abstract
The interaction between humic substances and poly(o-ethoxyaniline) (POEA), a conducting polymer, was investigated for both solution and self-assembled films. The results have shown that the humic substances induce a doping of POEA by protonation, as indicated by UV-Vis and Raman spectroscopies. The atomic force microscopy (AFM) studies on the self-assembled films have shown that the average roughness of the polymer film has increased after exposing it to humic substances (fulvic and humic acids), consistent with the interaction between POEA and humic substances. However, this change in morphology is reversible by washing the films with water in agreement with the electrical data allowing using this system in sensor applications. Here, the sensor formed by an array of different sensing units was able to detect and distinguish humic substances in aqueous solution, as shown by multivariate analysis (principal component analysis). The motivation to detect humic substance comes due to its importance in terms of quality control of water or soil.
Highlights
Polyaniline (PANI) and its derivatives are conducting polymers, which can be doped by protonic acid leading to great increase in the electrical conductivity and other related properties
The POEA was chemically synthesized using ammonium peroxydisulfate, 1.0 mol L-1 hydrochloric acid and excess of monomer according to the method described in the literature.[15]
The humic substances used were bought from Aldrich, and extracted in our laboratory, according to the method described elsewhere.[7,8]
Summary
Polyaniline (PANI) and its derivatives are conducting polymers, which can be doped by protonic acid leading to great increase in the electrical conductivity and other related properties These properties can be further changed by the interaction with other compounds, which influence the structure, morphology or doping features of the polymer.[1,2,3,4,5,6] In the case of PANI derivatives, e.g. poly(oethoxyaniline) (POEA), it has been shown the possibility. The sensing units were prepared using the SA technique as described elsewhere.[4] In the SA technique was used time scale as following: 1) 1 step of 1 minute (POEA-SA1); 2) 1 step of 3 min (POEA-SA2); 3) 1 step of 10 min (POEASA3) These experiments were carried out at pH 3.0 (HCl) using 1x10-3 mol L-1 POEA aqueous solution (Table 1). A Pirex® glass backer was used as electrochemical cell under air atmosphere
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