Synthesis and characterization of arginine-doped polyaniline/walnut shell hybrid composite with superior clean-up ability for chromium (VI) from aqueous media: Equilibrium, reusability and process optimization

Abstract Arginine-doped polyaniline@walnut shell (Arg-PANI@WNS) hybrid composite was prepared through interfacial polymerization reaction of aniline on the walnut shell particles surface in the presence of arginine. The as-synthetized composite characterization was made through energy dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and surface charge analysis. The Arg-PANI@WNS composite was subjected to Cr(VI) adsorption experiments from artificially contaminated solutions. Kinetics and equilibrium results were satisfactorily tailored via pseudo-second-order model and Freundlich isotherm. Optimum monolayer uptake capacities at pH 2 and 303 K were 450.53 and 562.83 mg·g−1 for PANI@WNS (prepared under otherwise identical conditions in the absence of arginine) and Arg-PANI@WNS, respectively. The Cr(VI) species binding mechanism was elucidated by the electrostatic interactions as a pivotal driving force. Desorption results demonstrated the excellent reusability of Arg-PANI@WNS composite during the clean-up of solutions containing Cr(VI) ions. Furthermore, Cr(VI) ions adsorption process was optimized via response surface methodology (RSM). Under optimized conditions, using Arg-PANI@WNS dose of 0.30 g·L−1 and Cr(VI) concentration of 50 mg·L−1 at pH 2 and 303 K, the predicted Cr(VI) ions removal efficiency was found to be 99.8%, which correlates reasonably well with actual values. Thus, the results obtained in the present study clearly revealed that the as-synthesized Arg-PANI@WNS hybrid composite could be taken as a potential filter to effectively clean-up hazardous Cr(VI) ions in industrial effluents.