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In the present research, a biopolymer Chitosan (C) grafted with ethylenediamine (EDA) and methyl acrylate (MA) were compared for the adsorption of Congo red dye from aqueous phase. The grafted chitosan product was characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and point of zero charge to study the change in mechanical and thermal properties. The effects of process variables like adsorbent loading, initial dye concentration, initial solution pH, contact time and temperature on adsorption phenomena were investigated. The equilibrium isotherm data was analyzed using Langmuir and Freundlich isotherm models, and the adsorption followed the Langmuir isotherm model (R 2  = 0.992 and 0.991 for EDAC and MAC, respectively). The maximum adsorption capacity of EDAC and MAC for Congo red uptake calculated from Langmuir isotherm model was 1607 mg/g and 1143 mg/g, respectively. The adsorption kinetics was studied using pseudo 1st and 2nd order models. Pseudo second order rate model provided the best fit for both grafted adsorbents with R 2 ≥0.99. The values of Gibbs free energy (-9.628 and -8.878 kJ/mol), enthalpy (44.9 and 42.2 kJ/mol) and entropy (0.18 and 0.17 J/mol·K) revealed spontaneous and endothermic adsorption of Congo red onto EDAC and MAC surface. The pollutant adsorption test indicated that chitosan grafting with ethylenediamine is superior to Methyl acrylate grafting agent., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In this study, chitosan was chemically modified with only diammonium phosphate (DAP) and DAP/EDTA (ethylenediaminetetraacetic acid) mixture for the removal of Pb(II) ions from aqueous solution. Modified chitosan forms were analyzed using thermo-gravimetric analyzer (TGA), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) to investigate the thermal degradation behavior, structural modifications, and the surface texture of the cross-linked chitosan adsorbents, respectively. The adsorption results were analyzed by well-known kinetic and isotherm models. The kinetics of metal adsorption followed the pseudo-second-order model. The maximum sorption capacities obtained from the Langmuir isotherm model were 126 mg/g for diammonium phosphate-modified Chitosan (DMC) and 137 mg/g for DAP/EDTA-modified chitosan (EDMC). The thermodynamic analysis showed that the metal removal process was endothermic in nature. [ABSTRACT FROM AUTHOR]

The research results summarize the potential of novel cross-linked chitosan for the removal of Congo red dye from an aqueous phase. Synthesized materials were characterized by FTIR, XRD, TGA, DSC and SEM. The effects of several process conditions like effect of adsorbent dose, contact time, initial solution pH and temperature were investigated. Equilibrium adsorption data was best fitted to Sips Isotherm model and maximum dye uptake was 1597 (mg/g) for diammonium tartrate modified chitosan (DMC) while 1447 (mg/g) for urea diammonium tartrate modified chitosan (UDMC). The adsorption kinetic data was well followed by pseudo-second-order kinetic model. The thermodynamic parameters (Gibbs energy, enthalpy and entropy) suggested the feasible and endothermic nature of Congo red adsorption over both adsorbents. The analyzed results indicated the promising ability of novel cross-linked chitosan for the removal of Congo red from aqueous phase and it can be extended to use in the treatment of textile wastewater. [ABSTRACT FROM AUTHOR]