Competent Heavy Metal Adsorption by Modified MWCNTs and Optimization Process by Experimental Design

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In this research, carboxylated multiwalled carbon nanotubes (c-MWCNTs) were improved with 5-amino-3-(2-thienyl) pyrazole (p-MWCNTs) for adsorption of Cd2+ and As3+ from aqueous solutions. Field emission scanning electron microscopy, Fourier transform infrared spectra spectroscopy, energy-dispersive X-ray spectroscopy, and thermogravimetric analysis were employed to characterize the p-MWCNTs. The central composite design inspected the effects of the pH, adsorbent dose, and initial metal ions concentration on the adsorption process. Further, the optimum adsorption conditions were acquired as 20 mg of the adsorbents, pH=7–8, and 20 mg·L−1 of metal ions concentration. Furthermore, for analysis of variance, the quadratic model was applied and indicated that pH was the most effective parameter in the adsorption process. Also, various adsorption isotherm models were examined. The results showed that the Langmuir isotherm correlated the experimental results in this work well, while kinetic data could be characterized by the pseudo-second-order adsorption rate kinetics. Moreover, the thermodynamic evaluations discovered that the sorption process was spontaneous and endothermic in nature. Finally, the adsorption–desorption study demonstrated a good regeneration capacity of the adsorbent for considering wastewater containing Cd2+ and As3+.