Thermodynamic Analysis of Reactive Red 198 Removal from Synthetic Wastewater by Using Multiwall Carbon Nanotubes

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Background: Industrial effluents the major contaminants of the environment and colored wastewaters from the textile industries are the main sources of environmental pollution. Objectives: The present study aimed to determine the appropriate MWCNTs dosage to adsorb RR-198 and identify the thermodynamic parameters such as the free energy (ΔG °), entropy (ΔS °), and enthalpy (ΔH °) changes during adsorption process at various temperatures. Materials and Methods: The present laboratory research investigated the effect of pH, adsorbent dose, temperature, initial dye concentration, and contact time on the adsorption process of RR-198 by MWCNTS. The values of thermodynamic parameters were determined to establish the adsorption mechanism. Also, the isotherm model has been investigated. Results: The RR-198 absorption rates were 33.26 and 222.88 mg/g, respectively for 20, and 200 mg/L dye concentration, at pH of 3, 600 mg/L dose of adsorbent, and 120 minutes time. In addition, the maximum absorption was observed at 600 mg/L dose of MWCNTs. Also, the studied dye absorption isotherm was fitted Freundlich model (R2 = 0.996 at 298K) and, the maximum adsorption capacities calculated by Freundlich model was 169.73 mg/g at 298K. All ΔG ° values were negative. The values of enthalpy (ΔH °) and entropy (ΔS °) were 38.119 KJ/mol, and 134.93 KJ/mol, respectively. Conclusions: The study results showed that by increasing the initial dye concentration and contact time, the adsorption capacity increased, as well. Moreover, the thermodynamic parameters (ΔH °, ΔG °, and ΔS °) revealed the endothermic sorption of RR-198 onto MWCNTs.