Modeling and optimization of Hg(II) adsorption conditions from aqueous solution by modified MWCNTs with 5-amino-3-(2-thienyl)pyrazole

In this work, the carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were chemically modified with 5-amino-3-(2-thienyl) pyrazole to synthesize MWCNTs-f and used to the adsorption of HG(II) ions from aqueous solutions. The adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron Microscope (FE-SEM), and thermal gravimetric analysis (TGA). The effects of pH, adsorbent dose, and initial ion concentration on the adsorption efficiency were investigated by central composite design. The optimum adsorption conditions were 20 mg of the adsorbents, pH=7-8, and 20 mg.L-1 of Hg(II) ions. The quadratic model was applied for analysis of variance and indicated that pH were the most effective parameter in the adsorption process. Also, various adsorption isotherm models were examined. The results show that the Langmuir isotherm fitted well the experimental results in this work, while kinetic data can be characterized by the pseudo-second-order rate kinetics. Moreover, negative values of ∆G° and positives ∆H° and ∆S° revealed that the adsorption reactions were spontaneous and endothermic with the increase in randomness. Desorption study revealed the favorable regeneration ability of adsorbents powders, even after 3 adsorption-desorption cycles

Keywords:

MWCNTs-COOH , 5-amino-3-(2-thienyl) pyrazole , mercury , aqueous solutions , removal