Comparison of Activated Carbon and Multiwalled Carbon Nanotubes for Efficient Removal of Eriochrome Cyanine R (ECR): Kinetic, Isotherm, and Thermodynamic Study of the Removal Process

Abstract

The objective of this study was to assess the suitability and efficiency of activated carbon (AC) and multiwalled carbon nanotube (MWCNT) for the removal of Eriochrome Cyanine R (ECR) molecules from aqueous solutions. The effect of different variables in the batch method as a function of solution pH, contact time, initial dye concentration, AC and MWCNT amount, temperature, electrolyte, and so forth by the optimization method has been investigated. ECR contents were determined using a UV–vis spectrophotometer before and after ECR adsorption on the AC and MWCNT, and the removal percentage was calculated using the difference in absorbance. The sorption processes followed the pseudosecond order in addition to intraparticle diffusion kinetics models with a good correlation coefficient with the overall entire adsorption of ECR on both adsorbents. Equilibrium data fit well with the Langmuir and Tempkin models with a maximum adsorption capacity based on the Langmuir equation of (40.6 and 95.2) mg·g–1 for AC and MWCNT, respectively. Thermodynamic parameters such as change in enthalpy (ΔH°) and entropy (ΔS°), activation energy (Ea), sticking probability (S*), and Gibbs free energy changes (ΔG°) were also calculated. Judgment based on the obtained results of thermodynamic values shows the spontaneous and endothermic nature adsorption processes on both adsorbents.