LAUSR

Abstract In this work, the carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were chemically modified with 3-aminopyrazole to synthesize MWCNTs-f. Then the three nanoadsorbents, i.e., MWCNTs, MWCNTs-COOH, and MWCNTs-f, have been separately used to the adsorption of Cd(II) ions from aqueous solutions. The adsorbents were characterized by Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron Microscope (FE-SEM), thermal gravimetric analysis (TGA), and Bruner-Emmet-Teller (BET) surface area measurement. The effects of pH, adsorbent dose, initial ion concentration, and temperature on adsorption efficiency were investigated by central composite design a subset of response surface methodology for experimental design to reducing the number of experiments runs having the interaction effects between the parameters. The optimum adsorption conditions for all adsorbents were 20 mg of the adsorbents, pH = 8–9, and 50 mg L −1 of Cd(II) ions at 45 °C. At the optimum conditions, Cd(II) ions removal efficiencies were 83.7, 65.9 and 35.7% for MWCNTs-f, MWCNTs-COOH, and MWCNTs, respectively. The quadratic model was applied for analysis of variance and indicated that pH and temperature were the most effective parameters in the adsorption process. The pseudo-second-order model was achieved from the adsorption kinetic studies. Also, various adsorption isotherm models at different temperatures were examined. The results show that the Langmuir isotherm is fitted suitably for the three adsorbents in this work and the best-selected isotherm models for the adsorption of Cd(II) ions by MWCNTs, MWCNTs-COOH, and MWCNTs-f were Langmuir, Dubinin–Radushkevich and Temkin models, respectively. Moreover, desorption study revealed the favorable regeneration ability of adsorbents powders, even after 3 adsorption-desorption cycles.