Estudos eletroquímicos em filmes de polianilina

Abstract

This dissertation addresses electrochemical studies on polyaniline (PANI) films, with special emphasis on investigating their properties when combined with lignin, aiming at applications in electrochemical sensors. Initially, the theoretical fundamentals of conductive polymers are presented, highlighting the structure and oxidation states of PANI, as well as the importance of lignin as a sustainable and abundant component. The experimental methods include the preparation of PANI and PANI/lignin films, characterized by techniques such as infrared spectroscopy (IR), UV-vis, cyclic voltammetry, and impedance spectroscopy. Cyclic voltammetry lacks sensitivity for detecting different concentrations of the ions used. The results demonstrate the influence of lignin on the modification of the electrochemical properties of PANI, and UV-vis and infrared techniques have enabled the suggestion of interaction between PANI and LIG. The results demonstrate the influence of lignin on the modification of the electrochemical properties of PANI. In addition, the dissertation explores the response of PANI films and their composites to the presence of different metal ions, such as Fe³⁺ and Cd²⁺, evaluating their potential application as sensors for detecting these analytes in aqueous solution. The Nyquist diagrams obtained by impedance spectroscopy show changes in the resistance and capacitance of the systems as a function of the composition of the film and the electrolyte. The sensitivity of the impedance spectroscopy technique enabled the detection of different concentrations of the ions Fe3+ used. However, due to the complexity of the porous polymeric electrode, it was difficult to evaluate the Nyquist diagrams, and it was decided to present the preliminary results of the 95PL composite (95% PANI and 5% LIG) and the Fe3+ ion only. Equivalent circuit models are discussed for a better understanding of the charge transport mechanisms. Finally, the study highlights the role of conductive polymeric materials in sensor devices, indicating that the incorporation of lignin may represent a viable strategy for improving sensitivity and selectivity for the Fe3+ ion, as well as contributing to the development of more sustainable and low-cost sensors. The results achieved reinforce the relevance of research into conductive polymers and open up new perspectives for environmental and technological applications.