Fabrication of a novel chitosan Schiff bases hydrogel derivatives for the removal of anionic dyes from wastewater
R.E. Khalifa, S. Aboulhadeed, Heba M. Ahmed, Ahmed M. Omer, Tamer M. Tamer, M.S. Mohy-Eldin
Abstract
ABSTRACT In this research, eco-friendly chitosan Schiff base hydrogel derivatives, as new adsorbents for anionic dye, Methyl orange (MO), were synthesized via coupling with 4-dimethylamino benzaldehyde (chitosan Schiff base (I)) and benzophenone (chitosan Schiff base (II)). The adsorbents’ structure was examined and characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. The MO adsorption percentage of the developed chitosan Schiff bases hydrogels compared to native chitosan was studied using a batch adsorption system under different adsorption conditions. The equilibrium time reached after 40 min for the chitosan Schiff bases adsorbents, while it was found 120 min for the chitosan adsorbent and the adsorption kinetics were found to follow the pseudo-second-order model. The values of α estimated by Elovich kinetic model are 2.2786 and 2.0489 mg/g which close from the experimental values; 2.415 mg/g for chitosan Schiff base (I), and chitosan Schiff base (II). Following up the adsorption mechanism performed using intraparticle diffusion model. The obtained results indicate the governed of the MO diffusion onto chitosan Schiff bases (I) and (II) by the boundary layer effect only. While that the removal process was governed by both surface removal and intraparticle diffusion in case of the chitosan adsorbent. At the same time, the Freundlich isotherm, Langmuir, and Temkin isotherm models have been applied to the adsorption data and were found to follow the Freundlich isotherm. The Langmuir monolayer maximum adsorption capacities were found 19.92, 19.34, and 22.37 mg/g for the chitosan, chitosan Schiff base (I), and chitosan Schiff base (II), respectively. The thermodynamic nature of the adsorption process was extracted using Van’t Hoff plot. The positive values for the ΔH indicate the endothermic nature of the adsorption process.