Adsorption Characteristics of Amaranth Onto Cetyltrimethylammonium Bromide—Modified Rice Husk in Aqueous Solution

An environment-friendly efficient adsorbent, hexadecyltrimethylammonium bromide-modified rice husk (CTAB-RH), was chosen to eliminate anionic azo dye amaranth from aqueous solution. The newly synthesized adsorbent CTAB-RH was characterized by the Fourier transform infrared spectroscopy. The point of zero charge (pH pzc ) value of CTAB-RH was estimated to be 5.85. Amaranth adsorption onto CTAB-RH was proven by the observations of field emission scanning electron microscopy (FE-SEM) coupling with energy dispersive X-ray spectroscopy (EDX). Adsorption kinetic experiments were conducted at the various contact time, solution pH, dye concentrations in solution, ionic strengths, and temperatures, respectively. The maximum dye adsorption was observed at pH 2. Amaranth adsorption kinetic data pursued a pseudo-second-order kinetic model. Equilibrium adsorption data followed the Langmuir isotherm model with a maximum 125 µmol/g dye adsorption capacity of CTAB-RH at 45°C. The activation energy of the present dye adsorption process was determined to be 18.71 kJ/mol. Thermodynamic study indicates that the amaranth dye adsorption onto CTAB-RH is a spontaneous endothermic process. Desorption of amaranth from dye-loaded CTAB-RH was performed in NaOH solution (pH 13) and finally, the recycled CTAB-RH was used without significant loss of its adsorption capacity.