Amino-dendritic and carboxyl functionalized halloysite nanotubes for highly efficient removal of cationic and anionic dyes: Kinetic, isotherm, and thermodynamic studies

Abstract

The surface functionalization of halloysite nanotubes (HNTs) is considered as one of the most critical strategies to enhance the adsorption capacity. Herein, amino-dendritic and carboxyl functionalized HNTs were successfully fabricated by convergent synthesis route and chemical coupling reaction, respectively. The chemical compositions of modified samples were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta potential, and BET analysis. The results show that the developed samples were successfully functionalized by succinic anhydride and poly(amidoamine) dendrimer (denoted as HNTs-SA and HNTs-SA-PAMAM). Then, the adsorption performances of functionalized adsorbents were systematically examined for the removal of Acid Red 1 (AR1) and Methylene Blue (MB) dyes as an anionic and cationic model dye, respectively. The maximum adsorption capacity of HNTs-SA for MB and HNTs-SA-PAMAM for AR1 was calculated to be 95.24 and 116.30 mg g−1 from the Langmuir model, respectively. While the adsorption mechanism for MB onto HNTs-SA and AR1onto HNTs-SA-PAMAM follow electrostatic interactions, the adsorption mechanism for MB onto HNTs-SA-PAMAM with the same cationic charge was explained by encapsulation in host-guest interaction. Furthermore, the kinetic and thermodynamic behaviors of cationic and anionic dyes on HNTs-SA and HNTs-SA-PAMAM were investigated. Desorption experiments have also been examined at different pH values, and the results indicated that modified nanoclay could remain stable at neutral pH. This study can provide an impulse for the researchers who regard important the efficient amino-functionalization of clay minerals with amine-terminated dendritic polymer for adsorption of dye pollutants.