Congo red removal by PANi/Bi2WO6 nanocomposites: Kinetic, equilibrium and thermodynamic studies

Polyaniline/Bismuth tungstate (PANi/Bi2WO6) nanocomposites were synthesized by a facile chemical method. The prepared samples were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-Ray Energy dispersive Spectroscopy (EDS) and Scanning electron microscopy (SEM). Bismuth tungstate co-modified by PANi was used as an eco-friedly adsorbent to remove anionic dye Congo red (CR) from aqueous solution. The obtained experimental results showed that the CR dye removal efficiency is significantly dependent on different physico-chemical conditions including initial pH, contact time, PANi weight content in PANi/Bi2WO6 nanocomposite, adsorbent dose, CR initial concentration and temperature. It was found that The CR adsorption efficiency increased from 13.74 to 92.03% for when the PANi content coated on Bi2WO6 nanoparticles was increased from 0 to 10 wt.%, respectively. This was explained by improvement in the amino groups of PANi, the creation of porous nanostructures and the increases in the specific surface area and decreases mean particle sizes. In addition, the experimental kinetic results were fitted by the pseudo-second-order model. Also, the equilibrium data were best represented by Redlich-Peterson and Langmuir isotherm models. The thermodynamic parameters indicate that the adsorption process was spontaneous and endothermic in nature. Furthermore, the adsorption capacity PANi/Bi2WO6 for CR dye was not significantly affected during four regeneration cycles.