Removal of Reactive Red 198 from aqueous solution by combined method multi-walled carbon nanotubes and zero-valent iron: Equilibrium, kinetics, and thermodynamic

Dyes often include toxic, carcinogenic compounds and are harmful to humans' health. Therefore, removal of dyes from textile industry wastewater is essential. The present study aimed to evaluate the efficiency of the combination of zero valent iron (ZVI) powder and multi-walled carbon nanotubes (MWCNTs) in the removal of Reactive Red 198 (RR198) dye from aqueous solution. This applied research was performed in a batch system in the laboratory scale. This study investigated the effect of various factors influencing dye removal, including contact time, pH, adsorbent dose, iron powder dose, initial dye concentration, and temperature. The equilibrium adsorption data were analyzed using three common adsorption models: Langmuir, Freundlich and Temkin. Besides, kinetic and thermodynamic parameters were used to establish the adsorption mechanism. The results showed, in pH = 3, contact time = 100 min, ZVI dose = 5000 mg·L− 1, and MWCNTs dose = 600 mg·L− 1 in 100 mg·L− 1 dye concentration, the adsorption efficiency increased to 99.16%. Also, adsorption kinetics was best described by the pseudo-second-order model. Equilibrium data fitted well with the Freundlich isotherm (R2 = 0.99). The negative values of ΔG0 and the positive value of ΔH0 (91.76) indicate that the RR198 adsorption process is spontaneous and endothermic. According to the results, the combination of MWCNTs and ZVI was highly efficient in the removal of azo dyes.