Kinetic model and thermodynamic study of Acid Red 1 entrapment at electropolymerised polypyrrole films

Abstract

This work is focussed on the determination of a kinetic model and the thermodynamic study of the electrochemical entrapment of the model azo dye, Acid Red 1, at conducting polypyrrole films, which is proposed as a potential green technology for treatment of azo dyes in industrial effluents. The entrapment kinetic data were found to follow a pseudosecond order model involving an intra-particle diffusion. However, the equilibrium data obtained for Acid Red 1 entrapment at polypyrrole did not obey any common surface adsorption models such as the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms. Accordingly, the entrapment process may lead to an enhanced quantity of dye embedded in a polypyrrole film, making it a more effective and efficient technology than those involving only adsorption. Similarly, dye leakage from polypyrrole film surface to a sample matrix will be easily prevented. For this treatment process, a negative ΔG∘ range between −1.46±0.78 and −2.94±0.24kJmol−1 at the corresponding temperature range of 298–318K, and a ΔH∘ of 20.5±2.5kJmol−1 indicate a spontaneous and endothermic entrapment process. Also, a positive ΔS∘ (73.6±8.2Jmol−1K−1) reveals increased randomness of the interface and an affinity of Acid Red 1 towards polypyrrole films. A low activation energy (7.67±0.80kJmol−1) confirms a physical process for Acid Red 1 entrapment at polypyrrole films.