Adsorption Studies of Reactive Green 19 from Aqueous Solutions by Polyaniline/Montmorillonite Nanocomposite

Polyaniline-based composites are potential candidates for the treatment of anionic azo dyes from an aqueous solution. However, the related adsorption mechanisms are not clearly delineated. Here, polyaniline/ montmorillonite (PANI/MMT) nanocomposite was synthesized by incorporating polyaniline (PANI) into the interlayers of montmorillonite (MMT). The nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results indicated that polymerization of the aniline monomer within the MMT gallery led to an expansion of basal spacing of the silicate layers. The prepared PANI/MMT nanocomposite was subsequently used for the removal of anionic azo dye Reactive Green 19 (RG19) from aqueous solutions. The adsorption of RG19 onto the PANI/MMT nanocomposite was consistent with the pseudo-second order kinetic model and the Langmuir isotherm model. The maximum adsorption capacity was found to be 46.88 mg/g at 25 °C, according to the linear regression analysis of the Langmuir isotherm. Thermodynamic parameters (Δ H ° = −12.35 kJ/mol, Δ S ° = −28.40 J/mol/K) revealed the spontaneous, exothermic, and enthalpy-driven nature of adsorption. Additionally, FTIR and X-ray photoelectron spectroscopy (XPS) analyses confirmed that the mechanism for adsorption of RG19 onto PANI/MMT nanocomposite involved hydrogen bonding and π - π interactions between the RG19 dye and adsorbent.