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

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^{{ring operator}} range between -1.46±0.78 and -2.94±0.24kJmol^-1 at the corresponding temperature range of 298-318K, and a δH^{{ring operator}} of 20.5±2.5kJmol^-1 indicate a spontaneous and endothermic entrapment process. Also, a positive δS^{{ring operator}} (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.