Adsorption of anionic methyl orange dye and lead(II) heavy metal ion by polyaniline-kapok fiber nanocomposite

Abstract

Low value natural hollow kapok fibers (KpF) were utilized as support for the synthesis of highly efficient polyaniline (PANI)-based adsorbents for heavy metal and ionic dye pollutants. The PANI-kapok (PANI-KpF) nanocomposite was prepared via in situ polymerization of aniline monomer in acidic condition using ammonium persulfate (APS) as the oxidizing agent. The morphology, wetting property and adsorption capacity of the PANI-KpF nanocomposites were tailored by performing NaClO2 pre-treatment and varying the APS to aniline ratio during coating. NaClO2 pre-treatment was found to promote the adhesion of aniline monomer on the surface of kapok, leading to high quality coating. On the other hand, the nanocomposite with [APS]/[aniline] = 1.4 exhibited the highest adsorption capacity. The effects of adsorbent dosage, initial solution pH, contact time, initial dye and heavy metal concentrations, and temperature were investigated through batch adsorption experiments. Kinetic studies indicate that the adsorption of MO and Pb(II) onto the PANI-KpF nanocomposite agrees well with the pseudo-second order kinetic model. Equilibrium isotherm studies show that the adsorption of both model pollutants follows the Langmuir isotherm model, and the calculated monolayer adsorption capacities are 136.75 and 63.60 mg/g for MO and Pb(II), respectively. Thermodynamic studies reveal that the adsorption of MO and Pb(II) are both endothermic and spontaneous.