Abstract
Natural peanut husk (NPH) and hexadecyltrimethylammonium bromide (CTAB)-modified peanut husk (MPH) were used to study the adsorption characteristics of amaranth in aqueous solution. NPH and MPH were characterized by Fourier transform infrared (FTIR) spectroscopy. The pHzpc values of NPH and MPH were estimated to be 5.06 and 5.96, respectively. The adsorption of amaranth onto both adsorbents was confirmed by the observations of field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDX) analysis. Adsorption kinetic experiments were conducted at various contact time, solution pH, initial dye concentration, temperature, and ionic strength, respectively. Dye adsorption kinetics pursued the pseudo-second-order kinetic model. Adsorption isotherms obeyed the Langmuir model with the highest dye adsorption capacity of 20.88 µmol/g for NPH at pH 2, and 117.65 µmol/g for MPH at pH 4. The values of activation energy (Ea) for the adsorption process were determined to be 48.68 kJ/mol for NPH and 16.92 kJ/mol for MPH, respectively. Thermodynamic data confirmed that amaranth adsorption onto both adsorbents was an endothermic spontaneous physisorption process. The release of amaranth from dye-loaded adsorbents was performed in HCl solution (pH 1) and the recycled adsorbents were utilized six times without significant loss of their adsorption capacity.
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