Non linear regression analysis and RSM modeling for removal of Cr (VI) from aqueous solution using PANI@WH composites

Abstract

An aquatic plant, water hyacinth was used after modification with poly-aniline (PANI@WH) as an adsorbent for removal of Cr (VI) from aqueous solution. The effect of pH, time, dose and concentration on Cr (VI) removal was investigated following batch adsorption process. The adsorption of Cr (VI) on PANI@WH adsorbent followed Freundlich adsorption isotherm as well as pseudo-second-order kinetic model. Maximum adsorption capacity obtained by isotherm has been achieved as 31.45 mgg−1 at 323K. Adsorption of Cr (VI) proceeds through film diffusion rather than intra-particle diffusion. Thermodynamic studies suggested endothermic and spontaneous nature of adsorption due to positive enthalpy and negative Gibbs free energy values. On the basis of the value of mean free energy, Gibb's free energy of adsorption and activation energy obtained in the present investigation suggested that adsorption of Cr (VI) on polyaniline coated water hyacinth occurs through physical adsorption. Surface characterization studies such as Field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared, Brunauer, Emmett and Teller surface area, X-ray photoelectron spectroscopy, X-ray diffractometer, atomic force microscopy and high resolution transmission electron microscopy illustrated adsorption mechanism of the adsorbent. The predicted % removal of Cr (VI) was obtain by response surface methodology model are compared with the experimental % removal of Cr (VI) obtained by batch adsorption process. Prepared composite adsorbent can be reused for several cycles and it gives 85% Cr (VI) removal efficiency even after 4th cycle which shows its good regeneration ability.