Dramatic enhancement in adsorption of congo red dye in polymer-nanoparticle composite of polyaniline-zinc titanate

Abstract

In this paper, we report a dramatic enhancement in the adsorptive removal of Congo Red (CR) dye by polyaniline-zinc titanate (PANI/ZTO) nanocomposite as compared with that when PANI or ZTO are used separately. The dye exhibited little adsorption in the presence of lab-synthesized pristine ZnTiO3 (ZTO) powder as adsorbent and somewhat moderate adsorption in the presence of neat polyaniline whereas excellent and much faster adsorption was exhibited in the presence of PANI/ZTO nanocomposite. The composite was prepared by carrying out the polymerization of aniline in the presence of ZTO suspensions. The composite samples were characterized using X-Ray diffraction, FT-IR Spectroscopy, Field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and Dynamic light spectroscopy, and the adsorption kinetics were studied using UV–Vis spectroscopy. The characterization data suggest that the adsorption of the CR dye gets enhanced because PANI chain molecules which are chiefly responsible for adsorption through hydrogen bonding and π–π interactions with the dye, get adsorbed/tethered on to the ZTO nanoparticles, and thereby overcome the mass transfer limitation by being better exposed to the dye molecules. The kinetics of adsorption followed the pseudo-second-order rate equation and the rate of adsorption was controlled by intra-particles diffusion. The isotherm was best described by the Langmuir model and the maximum adsorption was calculated to be 64.51 mg/g. The value of 7.80 kJ/mole obtained from the Dubinin–Radushkevich (D–R) model suggested the physisorption of CR onto PANI/ZTO nanocomposite. These results suggest that the mass of a polymeric substance, in general, can be better utilized for adsorption by suitably dispersing them over the surface of appropriate support nanoparticles.