The adsorption property and mechanism of phenyl/amine end-capped tetraaniline for alizarin red S

Phenyl/amine end-capped tetraaniline (TANI) was synthesized by chemical polymerization using ferric perchloride (FeCl₃) as the oxidant in HCl aqueous solution. And the TANI in emeraldine base state (TANI-EB) was obtained by dedoping the as-prepared TANI in the mixture solution of ammonium hydroxide and acetone. BET surface area (S_BET) and zeta potential analysis were used for the adsorption characterization of TANI-EB. The as-prepared TANI-EB was employed as the model compound of PANI to study the adsorption performance of the aniline polymers for organic dye (Alizarin Red S, ARS). In the adsorption study, the effects of pH, doses of adsorbent, and temperature on adsorption kinetics were investigated. The impact of salt ion (NaNO₃) concentration on the adsorption performance were also explored. Langmuir isotherm was found to be the most appropriate to describe ARS removal from water by TANI-EB adsorption. The adsorption capacity can be up to 236 mg/g and the equilibrium can reach within 30 min. Thermodynamic parameters, such as delta enthalpy (ΔH), entropy (ΔS), and free energy (ΔG), were also evaluated. Finally, the electrostatic effect and π-π interaction between ARS and the as-prepared TANI-EB in the adsorption process were investigated by UV-Vis spectrum and Fourier transform-infrared spectrum (FT-IR). It illustrates that the adsorption behavior of dye on PANI can be better understood by using TANI as the model compound of PANI. And TANI in EB phase can be as an adsorbent to remove dye from aqueous solution. [Figure not available: see fulltext.].