Removal of Congo Red Anionic Dye from Aqueous Solution Using Polyaniline/TiO2 and Polypyrrole/TiO2 Nanocomposites: Isotherm, Kinetic, and Thermodynamic Studies

Abstract

The present study seeks to investigate the capacity of polyaniline/titanium dioxide (PAn/TiO2) and Polypyrrole/titanium dioxide (PPy/TiO2) nano-adsorbents to adsorb Congo red anionic dye (CR) from aqueous solution. The variables effective in CR adsorption, including adsorbent dose, pH of the solution, contact time, initial dye concentration, and temperature were examined. The study yielded the result that a decrease in pH increases the adsorption capacity of both nano-adsorbents. The adsorbent dose and optimum contact time of PAn/TiO2 and PPy/TiO2 nano-adsorbents were [0.1 gr and 20 min] and [0.2 gr and 60 min], respectively. The adsorption kinetics was studied with the pseudo-first-order, pseudo-second-order, and Weber–Morris equations. Kinetic studies showed that the CR adsorption process onto both nano-adsorbents followed the pseudo-second-order kinetics model, which indicates that the adsorption process is chemisorption-controlled. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich Isotherms were applied to the adsorption data to estimate the maximum adsorption capacity as well as the intensity and energy of adsorption. The experimental data were best represented by Freundlich isotherm model compared to the other models. Analysis of data with Dubinin-Radushkevich isotherm showed that the adsorption of CR onto both nano-adsorbents is a chemisorption process. Moreover, Thermodynamic parameters such as ∆G, ∆H, and ∆S were calculated. The results showed that the adsorption of CR onto both nano-adsorbents was spontaneous and exothermic.